Fabrication of Sub 5-nm Plasmonic Nano-gap Nanostructures for Extreme
Confinement of Optical Fields
Jeetendra Gour1, Sebastian Beer1, Stefan Nolte1,2, Uwe Zeitner1,2
1. Institute of Applied Physics, Friedrich Schiller University Jena, Albert-Einstein-Str. 15, 07745 Jena, Germany
2. Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Albert-Einstein-Str. 7, 07745 Jena, Germany
E-mail: jeetendra.gour@uni-jena.de

Squeezing light into nanometric volumes or confining it into nanometer-wide gaps in plasmonic metals can lead to
extreme field enhancements, nonlinear optical effects, and optically induced electron tunneling. However, it has notbeen readily accessible to experimentalists due to the lack of reliable technology to realize uniform nano-gaps with
sub-5 nm resolution. In this work, we use a combination of atomic layer deposition [1] and ion beam etching based
planarization technique to obtain a reliable definition of the gap-size in a periodic gold grating.
In the paper, we introduce the technology process to realize structures with gap sizes in the sub-5 nm range andpresent our results demonstrating 3 nm wide, vertically oriented gaps in 1D grating structures in 30 nm thick gold
films. The scanning electron microscope image in Fig. 1(a) shows a top view of the realized 1D nano-gap array . The
scanning transmission electron micrograph in Fig. 1 (b) shows high resolution bright field cross-section of the nanogap confirming sub-5nm vertical gaps. The process is very flexible and we are working on its application for therealization of plasmonic antenna structures of various lateral geometries with sub-5nm gaps.
The fabricated nano-gap structures are intended to be used for the investigation of the nonlinear optical processes
such as wavelength conversion [2], optically induced electron tunneling and nonlinear resonance effects [3]. Further
potential applications could be found in near field imaging, optical switching etc.

Fig. 1 (a) Top scanning electron micrograph of sub-5 nm nano-gap grating structures (Period=600 nm). (b)High resolution TEM
image of the nano-gap cross-section.

References[1] Chen, X., Park, HR., Pelton, M. et al. 2013. Atomic layer lithography of wafer-scale nanogap arrays for extreme confinement of electromagnetic waves.
Nat Commun 4, 2361.
[2] Nezami,MS.,Yoo, D.,Hajisalem,G., Oh, SH. et. al. 2016. ACS Photonics 3 (8), 1461-1467.
[3] Kley, EB., et al. 2006. Nonlinear resonance effects on thin micro structured aluminum metal gratings by high power fs-laser pulses. Proc. of SPIE Vol.
6149 614902-1.

Geometry optimization of the magnetic
Purcell factor in high index dielectricnanostructures
Y. Brûlé1, P. Wiecha2, A. Cuche3, V. Paillard3, G. Colas des Francs1
1. Laboratoire Interdisciplinaire Carnot de Bourgogne, ICB-CNRS, Université de Bourgogne Franche-Comté, 21000 Dijon, France,
2. Laboratoire d’Analyse et d’Architecture des Systèmes, LAAS-CNRS, Université de Toulouse, 31031 Toulouse, France
3. Centre d’Élaboration de Matériaux et d’Études Structurales, CEMES-CNRS, Université de Toulouse, 31055 Toulouse, France
yoann.brule@u-bourgogne.fr

The coupling of the magnetic part of light to atoms is much weaker than the electric one. Hence, the development ofnovel applications based on magnetic response in the optical regime, such as negative-index metamaterials [1] orefficient nanoantennas [2], requires to focus on the engineering of the magnetic Local Density Of States (LDOS).

Fig. 1 Left : XY-plane projection of the optimized structure (orange : fixed core emitter, blue : Si nanopillars), Center : Evolution of themagnetic Purcell factor through the optimization iterations, Right : Scheme of the configuration extrapolated from the optimized
nanostructure.

In this work, we use evolutionary algorithms coupled to the Green’s Dyadic Method (GDM) in order to
optimize the geometry of planar silicon dielectric nanoantennas for controlling the emission rate of magnetic (MD) orelectric (ED) dipolar emitters (so-called Purcell factor) [3,4]. Depending on the nature and orientation of the dipoles,
different optimized shapes are obtained, all presenting regular and periodical features. To summarize, we distinguishdifferent behaviours in the near- and far-field zones of the dipolar emitter. In the far-field, we observe circular gratings
for all the configurations. As far as the near-field zone is concerned, we observe strong differences for ED and MD
emitters, with the presence or not of a Si core, that depends on both the dipole nature and orientation. Similar
configurations have been guessed in the literature but our work reveals that they are close to be optimal. We determine
the dimensions of a feasible 100 nm thickness planar dielectric silicon nanoantenna deposited on a glass substrate that
leads to a 2 · 103 enhancement of the spontaneous decay rate of the magnetic dipolar transition in Eu3+ ions. Finally,
to go beyond the "black box" optimization, we also discuss the physical origin of the obtained designs thanks to modal
analysis but also in relation to the deterministic design approach recently developed by Mignuzzi et al. in [5].
This work paves the way toward a better comprehension of the interaction between quantum emitters andhigh index dielectric nanoantennas and could lead to innovative applications such as optical negative-index
metamaterials or quantum technological components.
References[1] Shalaev, V. 2007, Optical negative-index metamaterials, Nat. Photonics 1, 41.
[2] Bidault, S. et al, 2019, Dielectric nanoantennas to manipulate solid-state light emission, J. Appl. Phys. 126, 094104.
[3] Wiecha, P. et al, 2022, “pyGDM” -python toolkit for nano-optics full-field simulations, Comput. Phys. Commun. 270, 108142.
[4] Brûlé, Y. et al, 2022, Magnetic and electric Purcell factor control through geometry optimization of high index dielectric nanostructure, inprep., arXiv:2201.01734.
[5] Mignuzzi, S. et al, 2019, Nanoscale design of the local density of optical states, Nano Lett., 19, 1613.

Imaging-Based Hydrogen Sensing Based on Fano-like Spatial Distribution ofTransmission in a Metal−Insulator−Metal Plasmonic Doppler Grating
Yi-Ju Chen1, Fan-Cheng Lin2, Ankit Kumar Singh1, Lei Ouyang1,3,4, Jer-Shing Huang1,2,3,5,6
1. Leibniz Institute of Photonic Technology, Albert-Einstein Straße 9, 07745 Jena, Germany
2. Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
3.Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Helmholtzweg 4, D-07743 Jena, Germany
4. State Key Laboratory of Biogeology and Environmental Geology, Faculty of Materials Science and Chemistry, China University ofGeosciences, Wuhan 430074, China
5. Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan
6. Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
E-mail: yi.ju.chen@uni-jena.de

To cope with global warming on a long-term basis, the role of sustainable and renewable energy becomes more
and more important. Hydrogen has been recognized as an alternative to fossil fuels and a potentially valuable tool fortackling climate change. Due to the low explosion concentration (4%), using hydrogen requires a robust and sensitive
sensor to monitor the concentration or detect the leakage of hydrogen. Optical hydrogen sensing methods are better
than electrical methods because they are free from spark generation and feasible for remote optical readout.
Conventional spectroscopic nanosensors require broadband excitation and spectrometers, rendering the devices bulky
and complex. An alternative is the monochromatic imaging-based sensor, which observes the optical response of aseries of spatially varying nanostructures such that the spatial intensity distribution provides the analytical signal. In
this case, the setup only requires an imaging system and a smartly designed platform to report the spatial distributionof analytical optical signals. [1-2]
In this work, a spatial intensity-based hydrogen sensing platform is presented based on Fano-like spatial
distribution of the transmission in a Pd-Al2O3-Au metal-insulator-metal plasmonic Doppler grating (MIM-PDG)(Fig.1a). [3] Due to the mode interference inside the MIM-PDG, a spatial Fano-like transmission intensity profile canbe observed at a single frequency (Fig.1b). Upon hydrogen absorption, the spatial transmission profiles changes (Fig.
1c). By analyzing the spatial profile with a non-spectral parametric Fano resonance model, the coupling and damping
parameters of the Fano resonance under different hydrogen concentrations can be obtained to establish a calibration
curve for quantitative analysis. Increasing the hydrogen absorption can lead to three different responses of thepresented MIM-PDG platform, namely increasing, decreasing, and unchanged transmission. While the first two cases
are useful for quantification of hydrogen absorption, the third case represents hydrogen insensitive gratings, which
provide stable optical response resistive to hydrogen absorption and can serve as a reference signal under fluctuatinghydrogen concentration.

Fig. 1 (a) The geometry and cross section of the Pd-Al2O3-Au MIM-PDG structure on an ITO coated coverslip. Only one circular ring iscompletely milling until the ITO layer. Rest rings are only milled into the Pd layer. The grating period continuously changes with the in-planeazimuthal angle (𝜑) from the largest period (∆𝑟 + 𝑑) at 𝜑 = 0° to the smallest period (∆𝑟 − 𝑑) at 𝜑 = 180°. (b) Monochromatic transmission
intensity image of the MIM-PDG illuminated by an unpolarized source at 633 nm. (c) Changes in the transmission intensity relative to 0%hydrogen as functions of azimuthal angle for 1% (red), 2% (green), 3% (blue), and 4% (cyan) hydrogen concentrations. The red (blue) arrows
mark the azimuthal angles, at which the transmission intensity increases (decreases) with increasing concentration of hydrogen.

References[1] See, K.-M. et al. 2017 Nanoscale 9, 10811-10819.
[2] Lin, F.-C. et al. 2019 Anal. Chem. 91, 9382-9387.
[3] Chen, Y.-J. et al. 2021 Adv. Opt. Mater. 9, 2100869.

Chiral Scatterometry on Gold-Nanohelicoid-on-Mirror Structures
Yilin Chen, Jianfang Wang*
Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China
E-mail: jfwang@phy.cuhk.edu.hk

Chiral molecules and nanostructures exhibiting unique chiroptical responses are promising materials for applications
in sensing, optical data storage, and displays [1]. Plasmonic chiral nanostructures demonstrate a diverse chiral response
as plasmons scatter and absorb circularly polarized light (CPL) differently. Chiral scatterometry of chiral nanoparticles
has been used to characterize their chiroptical properties [2]. Herein we focus on the effect of the dielectric properties
of substrates on the chiroptical scattering of gold nanohelicoids (GNHs). The GNHs were synthesized by a seedmediated growth method. They show distinct spectral and structural handedness. The scattering g-factor signals of the
GNHs-on-substrate structures were measured by single-particle differential dark-field scattering upon transfer of the
GNHs from silica substrates to gold films (Fig. 1a,b). The large localized electromagnetic enhancements can beachieved with the single GNHs separated from the gold film by a thin dielectric layer, resulting in larger differential
scattering (Fig. 1c). The degree of scattering g-factor of the GNH-on-mirror structures was up to 6 times larger thanthat for the ensemble (Fig. 1d). Averaging over the L-handed and D-handed GNHs with random orientations on gold
films also showed good mirror symmetry. We systematically studied the chiral scattering properties and the plasmonicmodes of the GNH-on-mirror structures. Our results of the substrate-based optical chirality in chiral nanosystems shed
new light on chiral light–matter interactions at substrate–nanostructure interfaces.

Fig. 1 (a) Schematic diagram and (b) dark-field scattering image of the GNH-on-mirror structures under CPL. (c) Measured
scattering spectra under left- (solid) and right-handed CPL (dashed) and (d) calculated scattering g-factor of the GNH-on-mirror
structure with a 1-nm-thickness dielectric spacer.

References[1] Lee H. E.; Ahn H. Y.; Mun J.; Lee, Y. Y.; Kim, M.; Cho, N. H.; Chang K.; Kim W. S.; Rho J.; Nam, K. T. 2018. Nature, 556, 360.
[2] Karst J.; Cho N. H.; Kim H.; Lee H. E.; Nam K. T.; Giessen, H.; Hentschel, M. 2019. ACS nano, 13, 8659.

THz Band-stop Filter using a Bragg Grating
Seyedali Dehghanian1 , Levi Smith1, Thomas Darcie1
1. Department of Electrical and Computer Engineering, University of Victoria, Victoria, BC V8P 5C2, Canada
E-mail: adehghanian@uvic.ca

The terahertz region of electromagnetic spectrum has become a significant research area due to its various
applications in science. Effective terahertz wave filtering in systems requires integrated THz System-On-Chip(TSoC) components. A low-loss, low-distortion and low-pulse-dispersion TSoC has been demonstrated using
Photoconductive Switch (PCS) devices bonded directly to a Coplanar Strip-line (CPS) transmission line definedusing photolithography on 1µm-thin Si3N4 membrane [1]. Based on this capability, it is now possible to develop
different components for the TSoC. Here, a novel THz Bragg Grating (TBG) integrated into the CPS transmission
line is presented to reject specific spectral components from a THz-bandwidth transmitted pulse. The Bragg
frequency was selected to be 0.8 THz.
Previous studies have demonstrated the operation of
band-stop filters in the THz frequency range, working at
a center frequency of 600 GHz. To characterize thesefilters, they were embedded in a micro-strip line
attached to photoconductive switches that serve as THz
emitters and detectors [2]. Some studies have also been
conducted to filter THz specific spectrum using othermaterials such as graphene or silicon [3,4]. This work
focuses on developing integrated, compact and efficient
TSoC technologies in which guided-wave THz systems
replace the current free-space THz systems.

Fig. 1 Structure of TBG integrated in CPS transmission line.

Here we analyze a structure compatible withexperimental fabrication. A 200 nm layer of gold (Au)
was applied to a Si3N4 membrane. There are N
identical cascaded sections of length Λ = λB /2 eef f in
the proposed THz Bragg filter (TBG). The length of the
TBG restricts increasing the number of sections
because a longer structure introduces more attenuation.
We set N to be 10, 20, and 40 to represent of longer
filters. Fig.1 illustrates the total structure and unit cell:each units cell consists of two quarter wave sections,L = Λ/4, and Z , and one half wave section, L = Λ/2,◦◦
1
and Z1. The system was modelled using a cascade of
two-port ABCD transmission matrices for lossy
transmission lines. The cascaded ABCD matrices werethen converted to S-parameters using standard methods
to which was used to characterize the reflection
coefficient (Fig. 2).
References

Fig. 2 Reflection coefficient of TBG for N equal to 10, 20 and 40[1] Smith, R., & Darcie, T. (2019). Demonstration of a low-distortion
terahertz system-on-chip using a CPS waveguide on a thin membrane
substrate. Optics Express, 27(10), 13653. https://doi.org/10.1364/oe.27.013653[2] Cunningham, J., Wood, C., Davies, A. G., Hunter, I., Linfield, E. H., & Beere, H. E. (2005, May 23). Terahertz frequency range band-stop
filters. AIP Publishing. Retrieved February 11, 2022, from https://aip.scitation.org/doi/10.1063/1.1938255[3] Ram, G. C., Sambaiah, P., Yuvaraj, S., & Kartikeyan, M. V. (2021, November 27). Tunable bandstop filter using graphene in terahertz
frequency band. AEU - International Journal of Electronics and Communications. Retrieved February 11, 2022, from https://www.sciencedirect.com/science/article/pii/S1434841121004441[4] Gao, W., Lee, W. S. L., Fumeaux, C., & Withayachumnankul, W. (2021, July 1). Effective-medium-clad Bragg grating filters. AIP Publishing.
Retrieved February 11, 2022, from https://aip.scitation.org/doi/10.1063/5.0051310

Deep subwavelength control of circularly polarized light by using
cathodoluminescence nanoscopy
Zheyu Fang1∗
1School of Physics, State Key Laboratory for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation
Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing 100871
E-mail: zhyfang@pku.edu.cn

Circularly polarized light is crucial for the modern physics research. Highly integrated nanophotonic device further
requires the fully control of circularly polarized light at nanoscale, which is limited via optical methods due to theoptical diffraction limit. Here, we report several approaches to manipulate circularly polarized light emission at deep
subwavelength scale by electron beam. Circularly polarized cathodoluminescence [1] and Smith-Purcell radiation canbe generated via precise stimulation on metal or hybrid nanostructures, while the chirality and direction of emission
can be actively controlled by shifting the electron impact position within 100 nm.
As a noninvasive technique, cathodoluminescence (CL) microscopy and spectroscopy with nanoscale resolution
have been successfully utilized in the electromagnetic mode investigation of plasmonic nanostructures. The scanningelectron beam functions as a local dipole source, enabling flexible and selectively mode excitation and control. Usingchiral CL nanoscopy, we found new chiroptical effects that is hidden in the near-field of the achiral nanostructure andreported a selective manipulation of photon spin angular momentum at a deep subwavelength scale via electroninduced optical spin Hall effect (OSHE) in Au nanoantennas [2,3]. The steering of OSHE under electron excitation
with nanoscale impinging position movement can be applied for a spin-dependent binary encoding.
Cathodoluminescence nanoscopy has been successfully used in the detection of local density of states in photonic
nanostructure as well, which directly determines the radiative properties of quantum emitters as Purcell effect. By
resolving radiated power into LCP and RCP contributions, chiral CL emissions are shown to directly render the chiralradiative LDOS that governs the radiative decay into either LCP or RCP channels [4], enabling the characterization ofchiral light-matter interactions like chiral photon emissions. Furthermore, we can use CL nanoscopy to control thevalley polarization in 2D transition metal dichalcogenides, tailor the optical properties of excitons [5].
These approaches may offer exciting opportunities for compact electron-driven source in opto-electronic circuitswith switchable chirality and open new prospects at the interface of nanophotonic and quantum optics.
References[1] Han, T. Y.; Zu, S.; Li, Z. W.; Jiang, M. L.; Zhu, X.; Fang, Z. Y., Reveal and Control of Chiral Cathodoluminescence at Subnanoscale. Nano
Letters 2018, 18 (1), 567-572.
[2] Zu, S.; Han, T. Y.; Jiang, M. L.; Lin, F.; Zhu, X.; Fang, Z. Y., Deep-Subwavelength Resolving and Manipulating of Hidden Chirality in
Achiral Nanostructures. Acs Nano 2018, 12 (4), 3908-3916.
[3] Chi, C.; Jiang, Q.; Liu, Z.; Zheng, L.; Jiang, M.; Zhang, H.; Lin, F.; Shen, B.; Fang, Z., Selectively steering photon spin angularmomentum via electron-induced optical spin Hall effect. Sci Adv 2021, 7 (18), eabf8011.
[4] Zu, S.; Han, T. Y.; Jiang, M. L.; Liu, Z. X.; Jiang, Q.; Lin, F.; Zhu, X.; Fang, Z. Y., Imaging of Plasmonic Chiral Radiative Local Densityof States with Cathodoluminescence Nanoscopy. Nano Letters 2019, 19 (2), 775-780.
[5] Zheng, L.; Liu, Z.; Liu, D.; Wang, X.; Li, Y.; Jiang, M.; Lin, F.; Zhang, H.; Shen, B.; Zhu, X.; Gong, Y.; Fang, Z., Deep subwavelength
control of valley polarized cathodoluminescence in h-BN/WSe2/h-BN heterostructure. Nat Commun 2021, 12 (1).

Fabry-Pérot Phonon Polaritons in Boron Nitride Nanotube Resonators
Cassandra Phillips, Yi-Fang Lai, Gilbert C. Walker*
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada*E-mail: gilbert.walker@utoronto.ca. Web: thewalkerlab.com

Phonon polaritons (PhPs) results from the coupling between optical photons and lattice vibrational phonons; PhPs
offer extreme confinement of optical fields and strong dispersion in the mid-infrared spectral region [1]. This strong
confinement can be used in SERS enhancement, driving reactions, sensor, hyperlensing, and other applications [2-6].
To study the propagation and interference of PhPs in a 1-D system, we employ scattering scanning near-field optical
microscopy (s-SNOM), analytical, and computational techniques to describe the resonance behavior observed in boron
nitride nanotubes (BNNTs), where strong optical anisotropy supports the propagation of volume-confined hyperbolic
PhPs (HPhPs) [7-9].
We observe that, in BNNTs of a sufficiently small length, the reflected standing waves from both terminals stronglyinterfere with one another, leading to large constructive enhancement at select wavelengths through Fabry-Pérot
interference (Fig. 1). The resonance of HPhPs results in the discretization of the dispersion relationship, and theirintensity can be nicely simulated both analytically and computationally using a Fabry-Pérot model. The 1-D nanoresonant behavior illustrates methods to increase and localize field strength at positions on a BNNT nanotube.
(a)

(b)

Fig. 1 (a) Experimental spatiospectral image of the imaginary optical response of a short (0.88 μm) BNNT in the mid-IR region, along with aschematic illustration of an AFM probe imaging the volume-confined PhPs via the scattered nearfield. (b) Schematic showing the appearance of
discretized, increasing resonant modes in a BNNT.

References[1] Basov, D. N.; Fogler, M. M.; Abajo, F. J. G. de. 2016. Science, 354 (6309)[2] Caldwell, J. D.; Lindsay, L.; Giannini, V.; Vurgaftman, I.; Reinecke, T. L.; Maier, S. A.; Glembocki, O. J. Low-Loss. 2015. Nanophotonics, 4(1), 44–68.
[3] Barnes, W. L. 2006. J. Opt. A: Pure Appl. Opt., 8 (4), S87–S93.
[4] Sanvitto, D.; Kéna-Cohen, S. 2016. Nature Mater, 15 (10), 1061–1073.
[5] Park, S.-M.; Lee, K. S.; Kim, J.-H.; Yeon, G. J.; Shin, H.-H.; Park, S.; Kim, Z. H. 2020. J. Phys. Chem. Lett., 11 (21), 9313–9320.
[6] Qiu, L.; Mandal, A.; Morshed, O.; Meidenbauer, M. T.; Girten, W.; Huo, P.; Vamivakas, A. N.; Krauss, T. D. 2021. J. Phys. Chem. Lett., 12(20), 5030–5038.
[7] Poddubny, A.; Iorsh, I.; Belov, P.; Kivshar, Y. 2013. Nat. Photonics, 7 (12), 948–957.
[8] Zapata-Rodríguez, C. J.; Miret, J. J.; Vuković, S.; Belić, M. R. 2013. Opt. Express, OE, 21 (16), 19113–19127.
[9] Ferrari, L.; Wu, C.; Lepage, D.; Zhang, X.; Liu, Z. 2015. Prog. Quantum Electron., 40, 1–40.

Investigating Spectrum of Double Nanoholes with Different Aperture and Gap
Sizes
Behnam Khosravi1, Reuven Gordon2
1. University of Victoria, 3800 Finnerty Road, Victoria, BC, Canada
2. University of Victoria, 3800 Finnerty Road, Victoria, BC, Canada
E-mail: rgordon@uvic.ca

Double nanoholes in metallic films can be used for trapping nano particles and single molecules in the gap between
the holes. An incident laser beam on the holes, induces plasmonic resonances that create a force in the gap. The force
brings in the particle and leads to a change in refractive index and transmission spectrum.
The resonance frequencies in the transmission spectrum depend on the size of the holes and the gap width inbetween. By tailoring these dimensions, the peaks can be shifted towards the desired frequency. These peaks are dueto the wedge and gap plasmonic resonances in the structure [1]. In order to maximize the transmission changes during
trapping of a particle, the laser wavelength should be at a slope in the transmission spectrum of the structure. An
increase or decrease in the transmission can be observed when the particle is trapped.
The fabrication process involves colloidal nanolithography with polystyrene nanospheres and gold deposition on a
glass surface, which forms double nano holes shown in Fig. 1A with a gap width of a few nanometers [2]. Nanosphereswith different sizes and etching times were used to make holes with different gap widths.
The model used in FDTD simulations consists of two holes and a gap in between, on a gold layer on glass. The
holes are filled with water and a nanoparticle was placed in the gap. Enlarging the holes diameter redshifts the peaks
for hole resonances. By changing the gap width, the gap resonance shifts correspondingly. Transmission spectrum of
a double nanohole with hole diameter of 150 nm is shown in Fig. 1B.

Fig. 1. A) SEM image of a double nanohole on a 70nm thick gold layer. B) FDTD simulation of transmission spectrum througha double nano hole of the same size as Fig. 1 (A).

The optical setup used for trapping nanoparticles, used a vertical sample placement and a novel cross-polarizedreflection geometry. The holes on the sample surface were visible using an infrared LED and a CMOS camera. The
laser beam observed in the camera, comes from the reflection from the sample surface. This reflection-based method
simplifies the alignment of microscope lenses and sample placement. A polarizing beam splitter have been used toobserve the polarization change of the laser beam reflection from double nanoholes.
References[1] Chen Y, Kotnala, A,Yu L,Zhang J, Gordon R, 2015, Opt. Express, 23, 30227-30236.
[2] Ravindranath AL, Shariatdoust MS, Mathew S, Gordon R, 2019, Opt. Express, 27, 16184-16194.

Digital harmonic holographic microscope for the study of nanostructures innonlinear regime
Serena Goldmann1, Samuel Grésillon1, Ignacio Izeddin1, Valentina Krachmalnicoff1, Gilles Tessier2, Yannick
De Wilde1,
1. Institut Langevin, ESPCI Paris, Université PSL, CNRS, 75005 Paris, France
2. Institut de la Vision – Sorbonne Université, 17 rue Moreau, 75012, Paris
E-mail : serena.goldmann@espci.fr

Digital holography is an imaging technique that enables a 3-dimensional reconstruction of the electromagnetic field
scattered by an object in both amplitude and phase. We demonstrated its use in microscopy for the full 3-D mappingof the scattered field from single nanostructures such as nano-antennas [1] and near-field probes [2], while detecting
the scattered field at the same frequency as the laser excitation. Since second harmonic generation (SHG) is a coherent
process, SHG light can also be used to generate interferences and holograms [3, 4].
Here, we describe the development of a harmonic holographic microscope. We apply SHG holography tonanoparticles and plasmonic nanostructures in order to obtain single-shot measurements of their second harmonic 3D
radiation pattern and to map intensity and phase variations near the sample. Using e.g. the angular spectrum
representation of optical fields [5], and assuming propagation in homogeneous media, the knowledge of the scatteredfield (amplitude and phase) in a given plane allows it to be calculated in any other plane, i.e. in 3D, by numerical backpropagation.
Since both the amplitude and the phase have to be measured to fully characterize the field in a plane, we chose tofocus on digital holography. The holographic setup is designed as an off-axis Mach Zehnder interferometer (Fig 1.a).
The incoming beam, generated by a Ti:Sapphire femtosecond laser oscillator, is divided into a reference and a sample
arm. The reference beam efficiently generates SHG in a BBO doubling crystal, while the sample beam yields SHG in
the sample itself. The beams are then recombined to interfere on an EM-CCD camera (Fig 1.b). Back-propagation
algorithms are computed and applied to the resulting hologram. Thus, we obtain the second harmonic radiation diagramof the sample via the 3-dimensional reconstruction of the SHG field generated by the sample excited by fs laser pulses.
In addition to providing 3D reconstruction, the harmonic holography microscope also benefits from aninterferometric amplification effect [6], making the method particularly well suited to measure the weak SHG signal
produced by nanostructures.
This research is supported by the French National Research Agency (ANR-20-CE24-0021), and LABEX WIFI underreferences ANR-10-LABX-24 and ANR-10-IDEX-0001-02 PSL*.

Fig 1.(a) Experimental setup schematics: BS, beam splitter, MO, microscope objective, M, mirror, L,lens, BBO, beta-barium borate crystal, BE, beam expander (b) Hologram

References[1] Suck, S. Y.; Collin, S.; Bardou, N.; De Wilde, Y.; Tessier, G. 2011. Optics Letters, 36, 849−851[2] Rahbany, N., Izeddin, I., Krachmalnicoff, V., Carminati, R., Tessier, G., De Wilde, Y. 2018. ACS Photonics, 5, 1539-1545.
[3] Pu Y., Centurion M., Psaltis D. 2008. Applied Optics, 47, A103-A110.
[4] Shaffer E., Pavillon N., Kühn J., Depeursinge C. 2009. Optics Letters, 34, 2450-2452.
[5] Novotny, L., and Hecht, B. Principles of Nano-optics. 2006. Cambridge University Press.
[6] Gross, M., Atlan, M. 2007. Optics Letters, 32, 909-911.

WS2-Flake-Sandwiched, Au-Nanodisk-Enabled High-Quality Fabry–Pérot
Nanoresonators for Photoluminescence Modulation
He Huang, Shasha Li, Jianfang Wang*
Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China
E-mail: jfwang@phy.cuhk.edu.hk

The increasing demand for compact and high-performance photonic devices drives the development of opticalresonators with nanoscale sizes and ultrahigh quality (Q) factors. Fabry–Pérot (FP) resonators, one of the most widelyemployed optical resonators, can support ultrahigh Q factors in the simple structure, which is particularly attractive
for applications in lasers, filters, and ultrasensitive sensors. However, the construction of FP resonators with bothnanoscale sizes and high Q factors still faces great challenges [1,2]. Herein we demonstrate the construction of FP
nanoresonators with a piece of WS2 flake sandwiched between Au nanodisks (NDs) and a Au film (Fig. 1a,b). The
atomically flat surfaces of the WS2 flake and the Au NDs benefit mirror alignment and boost Q the factor up to 76.
The single-Au-ND-enabled nanoresonators can support FP resonance modes with different orders in the visible region.
We systematically studied the optical properties and formation mechanism of the high-quality FP modes. The FP
modes were further hybridized with excitons in the WS2 flake spacer, allowing the modulation of the WS2 indirect
bandgap emission (Fig. 1c,d). Our results combine the advantages of plasmonic nanoparticles with those of FP
resonators, providing a promising platform for the development of compact nanophotonic devices such as tunable
nanolasers, smart sensors, and photonic circuit elements.

Fig. 1 (a) Schematic diagram of a single-Au-ND-enabled FP nanoresonator. The chromatic and red arrows indicate the incident
and scattered light, respectively. The magenta oblate spheroids indicate the formation of standing waves in the cavity, leading to
the excitation of the FP resonance. (b) Measured scattering spectrum of a nanoresonator. (c) Scanning electron microscopy (SEM)
image (left), scattering image taken with a 695 nm longpass filter (middle), and photoluminescence (PL) image (right) of four
Au-ND-enabled FP nanoresonators. The nanostructures are indicated by circles in the SEM image. The scale bars are 1 μm. (d)Measured PL spectra of different structures.

References[1] Schmidt, M. A.; Lei, D. Y.; Wondraczek, L.; Nazabal, V.; Maier, S. A. 2012. Nat. Commun. 3, 1108.
[2] Casalis de Pury, A.; Zheng, X.; Ojambati, O. S.; Trifonov, A.; Grosse, C.; Kleemann, M. E.; Babenko, V.; Purdie, D.; Taniguchi, T.;
Wantanabe, K.; Lombardo, A.; Vandenbosch, G. A. E.; Hofmann, S.; Baumberg, J. J. 2020. Phys. Rev. Lett. 124, 093901.

Manipulating the quantum field statistics of confine infrared fields via
ultrafast modulation of vibrational polaritons
Johan F. Triana1, Felipe Herrera1,2
1. Departamento de Física, Universidad de Santiago de Chile, Santiago, Chile
2. ANID-Millennium Institute for Research in Optics, Chile
E-mail: johan.triana@usach.cl

Demonstrations of strong and ultrastrong light-matter interaction in mid-infrared resonators have stimulated thesearch for control schemes that can be used to prepare target material and photonics states for a variety of applications
in chemistry [1]. We propose a scheme for modifying the photon number and field quadrature statistics of a confined
mid-IR electromagnetic field by modulating the vacuum frequency with femtosecond UV pulses [2]. The scheme relieson the transient modification of the carrier density of the field-confining materials and strong coupling between theconfined field and an ensemble of molecular vibrations. We study variations of the Mandel Q-factor and squeezingover sub-picosecond timescales by modulating the cavity frequency ~15%, resulting in squeezing factors of order ~1
dB for a system initially prepared in the stationary ground and lower polariton states [3]. We relate the predictedvariations of quantum field statistics to the type of dipolar structure and anharmonicity of the molecular vibrations.
Our work can stimulate the design of novel infrared devices at room temperature for applications in quantum metrology
and quantum information processing.

References[1] F. Herrera and J. Owrutsky. 2020. J. Chem. Phys. 152, 100902[2] J.F. Triana, F.J. Hernández and F. Herrera. 2020. J. Chem. Phys. 152, 234111[3] J.F. Triana, F. Herrera. 2022. New J. Phys. 24, 023008

Analytic approach to reflection and transmission of surface polaritons
Wonjae Choi1, Q-Han Park2
1,2. Department of Physics, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, Republic of Korea
E-mail: chldnjswo01@korea.ac.kr

Surface polaritons (SPs) such as graphene plasmons and exciton-polaritons are intrinsic electromagnetic modes
strongly confined to a two-dimensional (2D) material. When SPs propagating along the 2D material meet a 1D
boundary or a discontinuity, certain fractions of SPs become reflected and transmitted while the rest of them become
scattered. This fundamental phenomenon occurs ubiquitously when conducting near-field microscopy experiments for
2D materials or designing planar optical devices such as graphene-based plasmonic waveguide [1]. Due to theimprovement of computing power and the development of simulation programs, most studies resorted on numericalanalysis of the problem. Even in theoretical efforts, due to the complexity of the scattering process, theoretical studies
focused only on the specific case such as normal incidence [2-3]. Theoretical studies on general cases such as oblique
incidence, despite of its importance, have not been reported until now. Although numerical calculations provide fastand efficient revenue to understand the physical properties of SPs, accessing analytic solutions is essential inunderstanding the general properties of the system.
In this work, we present an analytic study on obliquely incident SPs to a boundary like Fig. 1(a). In Fig. 1(a), twodifferent 2D materials are bounded at x=0 and sandwiched between two optical media, and an SP is obliquely coming
into the boundary from x<0. We derived an analytic solution by using the Wiener-Hopf method [4]. To verify thesolution, we conducted a FEM simulation for obliquely incident SP in Fig. 1(b) by setting y-dependence to eiqy (q:transverse momentum) and plotted the x-component of the electric field. We compared the absolute value of the xcomponent of the electric field on z=0 about simulation and theory in Fig. 1(c). Comparisons to 3D cases are given in
Fig. 1(d), where we compared the solution with that of the Fresnel’s equation for TM polarization. We find that thisquasi-two-dimensional system shows slightly different features of reflection and transmission compared to those of
Fresnel’s equation. We provide an explanation underlying similarities and differences.

Fig. 1 (a): The geometry of the system. All materials are non-magnetic. Obliquely incident, reflected, and transmitted SPs arepresented. (b): Simulated result for obliquely incident SP. (c): Comparison between simulation results and theory. (d): Reflectance,transmittance, and their sum for the case of Fig. 1(a) (solid line) and Fresnel’s equation for TM polarization (dotted line).

In summary, we derived an analytic solution for obliquely incident SP and confirmed that the scattered fields makethe difference between this system and the conventional three-dimensional system. We expect that this work will
improve our fundamental understanding of reflection and transmission for SPs and provide insights when designingplanar optical devices.
References[1] Christensen, J., Manjavacas, A., Thongrattanasiri, S., Koppens, F. H., & García de Abajo, F. J. (2012). ACS nano, 6(1), 431-440.
[2] Siaber, S., Zonetti, S., & Sydoruk, O. (2019). Journal of Optics, 21(10), 105002.
[3] Rejaei, B., & Khavasi, A. (2015). Journal of Optics, 17(7), 075002.
[4] Margetis, D. (2020). Journal of Mathematical Physics, 61(6), 062901.

Double Nanohole Optical Tweezers Study of Conformation Changes of pr65
Samuel Mathew1, Ghazal Hajisalem1, Elham Babaei1, Michael Dobinson11, Reuven Gordon1
Mohsin Naqvi2, Janet Kumita 2
1. Electrical and Computer Engineering, University of Victoria, Victoria BC, V8W 2Y2 Canada
2. Pharmacology, University of Cambridge, Cambridge, United Kingdom
E-mail: samuelmathew@uvic.ca

Pr65 is the 65 KDa structural subunit of protein phosphatase PP2A [1] implicated in enzyme action [1] andcancer [2]. Previous research, for example [1], suggests that the elastic properties of pr65 are crucial both for its
function and characterization, yet a literature search of its elastic constant returns no result.
This study attempts to fill this gap. Furthermore, because the magnitude of external force found to produce
measurable conformation changes in pr65 [1] is well within the range of force exerted by optical tweezers [3], it does
this by trapping pr65 in a double nanohole (DNH) optical tweezers and analyzing the time series of the lightintensities scattered by the trapped pr65. Two discrete jumps were observed, consistent with the fact that protein
conformation change is subject to overcoming a free energy barrier [4].
Previous studies such as [1] show that pr65 unfolds under tension, and we attribute the observed jumps to theunfolding of pr65 due to electrostriction in the cusp of our double nanohole optical tweezers. We found that the change
in the polarizability of pr65 following this unfolding is roughly 3.2 × 10-36 Cm-2V-1, and estimate that the flexural
stiffness of pr65 in the regime of our experiment is about 50 mN/m, corresponding to a flexural oscillation frequency
of about 0.30 cm-1, comparable to 0.37 cm-1 predicted by [1] based on normal mode analysis. A snapshot of our results
is shown in Figure 1 below.

Fig. 1 (a) Double nanohole (DNH) aperture; (b) Time series of scattered intensity; (c) Zoom-in showing two discrete jumps; (d)Autocorrelograms of the time series for the first jump (magenta solid line) and the second jump (black solid line).

References[1] A. Grinthal, I. Adamovic, B. K. M. Weiner and N. Kleckner, "PR65, the HEAT-repeat scaffold of phosphase PP2A, is an elastic connector
that links force and catalysis," Proceedings of the National Academy of Sciences, vol. 107, no. 6, pp. 2467 - 2472, 2010.
[2] M. R. Groves, N. Hanlon, P. Turowski, B. A. Hemmings and D. Barford, "The structure of the protein phosphatase 2a pr65/a subunit reveals
the," Cell, vol. 96, pp. 99 - 110, 1999.
[3] M. C. Williams, "Measuring Piconewton Forces," 2002. [Online]. Available:
https://www.biophysics.org/Portals/0/BPSAssets/Articles/williams.pdf. [Accessed 7 February 2022].
[4] A. N. Naganathan, R. Perez-Jimenez, V. Muñoz and J. M. Sanchez-Ruiz, "Estimation of protein folding free energy barriers fromcalorimetric data by multi-model bayesian analysis," Phys. Chem. Chem. Phys, vol. 13, p. 17064 –17076, 2011.

Isolating Er3+-Doped Nanocrystals for single photon Sources at 1550 nm
Zohreh Sharifi1, Reuven Gordon2
1. Department of Electrical Engineering, University of Victoria, Victoria, Canada
2. Department of Electrical Engineering, University of Victoria, Victoria, Canada
E-mail: rgordon@uvic.ca

Single-photon sources which can be created by isolation individual atoms and atom-like defects are required forquantum technologies. One of the promising choices for single photon sources are erbium ions which produce single
photons at low-loss fiber optic wavelengths, but they have low emission rates. Gold double nanoholes (DNHs) can beused to enhance the emission of single erbium emitters. Here, we tune the size of DNHs to achieve the bestenhancement to show visible emission from single nanocrystals at 1550 nm using an optical tweezers. We observe
discrete levels of emission at 1550 nm for Erbium- doped nanocrystals with low numbers of emitters and demonstrateisolating single emitters.
In our previous work [1], we demonstrated that the plasmonic resonances of DNH apertures in a gold film can betuned to much more enhancement of the erbium emitters emission compared to rectangular apertures [2]. Here, we use
the same procedure and techniques to create DNH apertures with different cusp separations and use the same opticaltrapping setup to achieve more enhancement at 1550 nm.
Fig. 1 a) shows the emission 23.4 nm Yb–Er-doped NaYF4 nanocrystals using DNH apertures with varying averagecusp separations. It illustrates how the size and shape of the aperture can affect the overall emission. Fig. 1 b) showsthe emission at 1550 nm of single nanocrystals as measured with a 1 s integration time. It proves that the emission isseparated into discrete levels. We attribute these levels to the discrete numbers of erbium emitters in the nanocrystals,
from zero to six individual active emitters.

Fig. 1 a) Emission from 23.4 nm nanocrystals at 1550 nm for varying DNH cusp separations. b) Emission counts from nanocrystals showing discretelevels corresponding to different amounts of active erbium emitters. Collected by a spectrometer with 1 s acquisition time.

The discrete levels of emission can be used to identify and isolate single active emitters and is a step towards
reliable production of single photon sources at 1550 nm, the low-loss fiber optic band.

References[1] Sharifi, Z., Dobinson, M., Hajisalem, G., Shariatdoust, M.S., Frencken, A.L., van Veggel, F.C. and Gordon, R., 2021. Isolating and enhancing
single-photon emitters for 1550 nm quantum light sources using double nanohole optical tweezers. The Journal of Chemical Physics, 154(18),p.184204.
[2] Alizadehkhaledi, A., Frencken, A.L., van Veggel, F.C. and Gordon, R., 2019. Isolating nanocrystals with an individual erbium emitter: A routeto a stable single-photon source at 1550 nm wavelength. Nano Letters, 20(2), pp.1018-1022.

Enantioselective optical trapping by elliptical plasmonic nanoholes
Zhan-Hong Lin1, Jiwei Zhang2, Ankit Kumar Singh1, Xiaofei Wu1, and Jer-Shing Huang1,3,4,5
1. Leibniz Institute of Photonic Technology, Albert-Einstein Straße 9, 07745 Jena, Germany
2. MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, and Shaanxi Key Laboratory of Optical
Information Technology, School of Physical Science and Technology, Northwestern Polytechnical University, Xi’an 710129, China
3. Abbe Center of Photonics, Friedrich-Schiller University Jena, Jena, Germany
4. Research Center for Applied Sciences, Academia Sinica, 128 Sec. 2, Academia Road, Nankang District, 11529 Taipei, Taiwan
5. Department of Electrophysics, National Chiao Tung University, 1001 University Road, 30010 Hsinchu, Taiwan
E-mail: zhan-hong.lin@leibniz-ipht.deCircular dichroism (CD) is one of the key chiral characteristics to distinguish chiral chemical or biological systems
between their enantiomers. However, the sensitivity of analytical methods based on chiral light-matter interaction isusually low due to the size mismatch between the light helix and the size of molecular chiral domains. Plasmonicnanostructures offer the possibility to engineer optical near fields [1] and enhance light-matter interaction. Realizationof efficient enhancement requires, however, the presence of target analyte in the area of the enhanced field, which istypically limited by free diffusion. Therefore, it is important to rationally design nanostructures to simultaneously
provide plasmon-enhanced chiroptical field for CD [2, 3] and optical trapping force [4] to trap the target in the hotspot.
Here, we propose using elliptical nanoholes on an extended gold film as a simple yet effective achiral platform todemonstrate chiroptical analysis [5]. For a linearly polarized light, a well-designed elliptical nanohole cansimultaneously generate chiral near-field for chiroptical analysis and act as a nano-optical trap to capture dielectricand plasmonic nanospheres (Fig. 1 a). The figure also shows two distinct optical potential (Uxy) landscapes of the same
elliptical nanohole upon linear polarization illumination. Depending on the chirality (κ) of the nanoparticle, the inplane trapping potential can be attractive (Fig. 1 b) or repulsive (Fig. 1 c) to the particle, making the elliptical nanohole
an effective enantioselective optical trap.

Fig. 1 Plasmonic optical trap by elliptical nanohole. (a) Schematic of the elliptical nanohole on the gold film. (b, c) Trapping
potential contour maps of the in-plane optical force (𝐹𝐹𝑥𝑥 and 𝐹𝐹𝑦𝑦) exerted on a chiral PS nanosphere (diameter = 20 nm). The
chirality parameter κ is ±1. The red and blue traces on the x-z and y-z projection planes are the cross-sectional potential cut by y
= 0 and x = 0 planes. The black dashed lines on the x-y projection planes mark the boundaries of the elliptical nanohole. The
calculations were made for an injected power in the aperture of 1 W.

Using this achiral platform with linearly polarized illumination, false chiroptical signals due to nanostructures canbe eliminated. Moreover, the compatibility of the platform with typical optical microscopes is greatly improved
because the problems due to the distortion of circularly polarized light by the optics of a microscope are avoided. The
platform is ideal for sensitive chiroptical analysis in combination with nanoparticles-based solid-state extraction andpre-concentration, which further enhances chemical selectivity and sensitivity.
References[1] Biagioni, P., Huang, J. -S., Duò, L., Finazzi, M., and Hecht, B., 2009 Phys. Rev. Lett. 102, 256801.
[2] Schäferling, M., Dregely, D., Hentschel, M., and Giessen, H., 2012 Phys. Rev. X 2, 031010.
[3] Lin, D. and Huang, J.-S., 2014 Optics Express 22, 7434-7445.
[4] Juan, M. L., Gordon, R., Pang, Y., Eftekhari, F., and Quidant, R., 2009 Nat. Phys. 5, 915-919.
[5] Lin, Z.-H., Zhang J., and Huang J.-S., 2021 Nanoscale 13, 9185

Probing Raman active acoustic vibrations of single molecule protein: PR65
Elham Babaei1, Ghazal Hajisalem1, Burak Kaynak2, Pemra Doruker2, Mohsin M. Naqvi3, Janet Kumita3, Feng-Yu
Wang4, Jhih-Hong Cheng4, Che-Min Wu4, Shang-Hua Yang4, Ivet Bahar2, Laura Itzhaki3, Reuven Gordon1
1. University of Victoria, Victoria, Canada
2. University of Pittsburgh, Pittsburgh, United States
3. University of Cambridge, Cambridge, United Kingdom
4. National Tsing Hua University, Hsinchu, Taiwan
E-mail: elhambabaei@uvic.ca

We demonstrate Extraordinary Acoustic Raman (EAR) vibrational modes of PR65. Two lasers have been used inorder to sweep the beat frequency to excite the single molecule in the double nanohole optical tweezer setup. EAR
spectrum shows that the modes of vibration are at frequencies: 11.1 GHz, 20.8 GHz, 31.5 GHz, 38.0 GHz which arein agreement with results of Anisotropic Network Model (ANM) simulation. This technique is label free and single
molecule compared to other methods of characterization of proteins. Normal mode analysis (NMA) reveals that tumor
suppressor protein phosphate 2A (PP2A) conformation fluctuation due to forces imposed from mechanical andchemical energy inputs is dominated by elastic deformation of its subunit PR65. Characterizing natural repeat proteins
PR65 is of highest importance since they are involved in many cellular processes.

Fig. 1 a) Trapping event of PR65 using optical trapping setup. b) EARs of PR65. Solid lines are the experimental measurements
and the dashed lines show the ANM results

References[1] Wheaton, S., Gelfand, R.M. and Gordon, R., 2015. Probing the Raman-active acoustic vibrations of nanoparticles with extraordinary spectral
resolution. Nature Photonics, 9(1), pp.68-72.
[2] DeWolf, T. and Gordon, R., 2016. Theory of acoustic Raman modes in proteins. Physical Review Letters, 117(13), p.138101.
[3] Kaynak, B.T., Bahar, I. and Doruker, P., 2020. Essential site scanning analysis: a new approach for detecting sites that modulate the dispersion
of protein global motions. Computational and structural biotechnology journal, 18, pp.1577-1586.
[4] Kaynak, B.T., Zhang, S., Bahar, I. and Doruker, P., 2021. ClustENMD: efficient sampling of biomolecular conformational space at atomic
resolution. Bioinformatics, 37(21), pp.3956-3958.

Coupling between Perovskite Quantum Dots in an Plasmonic Optical Tweezer
Parinaz Moazzezi123, Hao Zhang12, Brett Henderson23, Vishal Yeddu23, Cristina Cordoba24, Arthur
Blackburn24, Makhsud I. Saidaminov123, Irina Paci23 and Reuven Gordon12
1. Department of Electrical and Computer Engineering, University of Victoria, 3800 Finnerty Road, Victoria, V8P 5C2, British Columbia, Canada
2. Centre for Advanced Materials & Related Technologies (CAMTEC), University of Victoria, 3800 Finnerty Road, Victoria, V8P 5C2, British
Columbia, Canada
3. Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, V8P 5C2, British Columbia, Canada
4. Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, V8P 5C2, British Columbia, Canada
E-mail: rgordon@uvic.ca

All inorganic halide Perovskite (CsPbBr3) nanocrystals (NCs) have efficient single photon emission and longcoherence times which makes them of interest for quantum information application [1]. Their strong coupling also
allows for non-classical emission, such as superfluorescence [2]. To understand the coupling better, it is of interest to
study the coupling between two such emitters, and this may be used to create entangled states [3].
In this paper we measure the coupling between two PQDs by an optical tweezer trapping setup [4]. We sequentiallytrap two dots in a single trap and measure the change in emission wavelength and intensity. Fig 1. Shows the
distribution of two-photon photoluminescence for single and double PQD trapping. Double PQD trapping is identified
via jumps recorded on an avalanche photo diode. The emission intensity for double PQDs is more than double incomparison with single PQD trapping, and also there is systematic red-shift in the emission. The direct electronic
coupling (left figure) does not explain the observed shift, and so other mechanisms are required to explain these results.

Fig. 1 (a) spectra of single dot trapping and double dots trapping. The areas filled with blue and green stands for the experiment data at eachsampling (fit with Gauss function). The dotted line in red and black are fitted by Gauss function from multiple spectra. (b) Quantum calculation ofenergy shift. Inset shows the wavefunction distribution for the two dots.

References
[1]
[2]
[3]
[4]

H. Utzat et al., “Coherent single-photon emission from colloidal lead halide perovskite quantum dots.,”
Science, vol. 363, no. 6431, pp. 1068–1072, Mar. 2019, doi: 10.1126/science.aau7392.
G. Rainò, M. A. Becker, M. I. Bodnarchuk, R. F. Mahrt, M. V Kovalenko, and T. Stöferle,“Superfluorescence from lead halide perovskite quantum dot superlattices.,” Nature, vol. 563, no. 7733, pp.
671–675, Nov. 2018, doi: 10.1038/s41586-018-0683-0.
B. M. et al., “Coupling and Entangling of Quantum States in Quantum Dot Molecules,” Science (80-. )., vol.
291, no. 5503, pp. 451–453, Jan. 2001, doi: 10.1126/science.291.5503.451.
A. L. Ravindranath, M. S. Shariatdoust, S. Mathew, and R. Gordon, “Colloidal lithography double-nanohole
optical trapping of nanoparticles and proteins.,” Opt. Express, vol. 27, no. 11, pp. 16184–16194, May 2019,
doi: 10.1364/OE.27.016184.

Nanoaperture optical fiber tweezers fabricated with a low-cost colloidal
pattern transfer method
Michael Dobinson1,2, Reuven Gordon1,2
1. Department of Electrical and Computer Engineering, University of Victoria, Victoria, BC, V8P 5C2, Canada
2. Centre for Advanced Materials and Related Technology (CAMTEC), University of Victoria, Victoria, BC, V8P 5C2, Canada
E-mail: rgordon@uvic.ca

Optical trapping using nanoapertures such as double nanoholes (DNHs) is a useful technique for analysing
proteins and other small particles which unfortunately is inaccessible for many due to the complicated optical setup
and nanofabrication requirements [1]. Integrating a DNH aperture on the tip of an optical fiber greatly simplifies thetechnique as it allows for fully fiber-based trapping systems which require only minimal optics experience. Previous
works have demonstrated nanoaperture optical fiber tweezers, but fabrication has been based on expensive top-down
approaches [2–4]. This work presents a method to fabricate nanoaperture optical fiber tweezers by colloidal patterntransfer with a low-cost pattern fabricated using colloidal lithography. Results of optical trapping using a fabricatednanoaperture fiber tweezer with a polystyrene nanoparticle size standard are also presented.
A gold film pattern of DNH apertures is first produced using colloidal lithography as previously presented by ourgroup [5]. This pattern contains single, double, and multiple nanoholes in the gold film. Scanning electron
microscopy or polarization analysis [6] can be used to find suitable DNHs, where they are separated by more than
the fiber core radius, 4.1 μm. A cleaved single-mode fiber is aligned to the DNH by monitoring transmission
through the fiber. The face of the optical fiber is coated with UV-cured optical adhesive and moved to contact thegold surface. The glue is cured using UV light and the fiber is lifted to detach the gold from the glass substrate. Fig.
1a shows a schematic of the final device with the DNH affixed to the tip of the optical fiber.
A fiber nanoaperture optical tweezer was used with a fiber laser to optically trap a 40 nm polystyrene
nanoparticle by dipping the tip of the fiber into solution. Fig. 1b shows the transmission through the aperture whichshows trapping with a 0.5% increase in the transmission as well as 2.4% increase in the signal variation, measured
by the full width at half maximum of a Gaussian fit. The laser is turned off at 85 s and back on at 110 s which showsa return to the low variation state, indicating that the particle was released. Fiber-based nanoaperture tweezers
simplify trapping with nanoapertures and the colloidal pattern transfer fabrication method presented here shows a
low-cost route to producing these devices.

Fig. 1. Nanoaperture optical fiber tweezers. (a) Schematic drawing of the structure at the tip of a cleaved optical fiber. (b)Normalized transmission signal (black) through the aperture with 40 nm polystyrene nanoparticles. The signal is filtered andshown before trapping in red, and during trapping in blue.

References[1] Gordon, R. 2019. Opt. & Laser Tech., vol. 109, pp. 328–335.
[2] Gelfand, R.M., Wheaton, S., and Gordon, R. 2014. Opt. Let., vol. 39, no. 22, pp. 6415–6417.
[3] Ehtaiba, J.M. and Gordon, R. 2019. Opt. Express, vol. 27, no. 10, pp. 14112–14120.
[4] Berthelot, J., Aćimović, S., Juan, M., Kreuzer, M.P., Renger, J., and Quidant, R. 2014. Nature Nanotech, vol. 9, pp. 295–299.
[5] Ravindranath, A.L., Shariatdoust, M.S., Mathew, S., and Gordon, R. 2019. Opt. Express, vol. 27, no. 11, pp. 16184–16194.
[6] Hajisalem, G., Babaei, E., Dobinson, M., Iwamoto, S., Sharifi, Z., Eby, J., Synakewicz, M., Itzhaki, L.S., and Gordon, R. 2022. Opt. Express,
vol. 30, no. 3, pp. 3760–3769.

Breakdown of spin-to-helicity locking at the nanoscale in topological photonic
crystal edge states
Sonakshi Arora1, Thomas Bauer1, René Barcyzk2, Nikhil Parrapurath2, Ewold Verhagen2, Kobus Kuipers1,
1 Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
2. Center for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherland
E-mail: s.arora@tudelft.nl

Topological photonics recently gained widespread attention due to its potential for robust information transport,with on-chip photonic modes protected by a given topological invariant, or pseudo-spin [1] and near-unity far field
helicity [2]. Unidirectional emission is achieved, in general, by strong coupling of a quantum emitter with circularly
polarized dipole moment to the local polarization state of a photonic mode. In our work [3], we use a photonic crystal
based approach emulating quantum spin-Hall (QSHE) [4] resulting in symmetry-protected edge states present at theinterface of topologically different photonic crystal lattices. With near-field microscopy we quantitatively investigate
the photonic edge eigenstates and their transport properties.
We investigate the properties of the topologically-protected edge states at the interface of topologically non-equivalent
photonic crystals lattices: shrunken and expanded(top left inset Fig. 1.). The interface supports
counter-propagating topological states that mimic
the QSHE (Fig. 1). By directly measuring theindividual in-plane field components, we obtainsignatures of the underlying photonic spin-orbit
coupling, manifested by spatially-varying spin
densities (right inset Fig. 1). These observations
are in striking contrast to the far-field helicity ofthe edge state which is uniquely linked to its
pseudo-spin.
Fig. 1 Measured near-field amplitude map of a QSHE edge state that lies
The contrast between near- and far-field
below the light line. Inset: SEM image of the two lattices, ‘shrunken’ andobservations can be understood from the measured‘expanded’. Dashed box shows the experimentally measured z-component
and calculated band structure of the edge statesof the spin density Sz ∝ ℑ(E∗×E)z, normalized to the maximum absolutevalue shown in the image.
(see dispersion relation in Fig. 2; [5]).The Bloch
harmonic within the first Brillouin zone also called
the fundamental harmonic contributes to unambiguous near-unity spin (SFF) in the far-field. This is the only Bloch
harmonic interrogated in far-field measurements (Fig.2 (b)). However, as the higher-order Bloch harmonics are added
to construct the actual Bloch mode, the global spin SNF is reduced by a factor of 30 and for certain frequencies, SNF iseven flipped compared to the pseudo-spin measured in the far-field SFF. We experimentally reveal the influence of
higher-order Bloch harmonics in spin inhomogeneity, leading to a breakdown in the coupling between local helicity
and global spin.

Fig. 2 Numerically simulated dispersion relation where the edge state
eigen frequencies are color coded with the estimated (a) near-field and (b)far-field optical spin S.

References

Our findings demonstrate that in order to employ
these systems for unambiguous spin-dependent
photon transport from coupled chiral emitters, thelocal structure of the edge state’s spin density must
be taken into account. This has profoundconsequences on the design of topological photonic
quantum networks and provides a route towards
engineering more robust topologically protectedchiral interfaces. A detailed study of this spin-tohelicity breakdown might furthermore lead to novel
concepts in understanding dissipative mechanisms
in electronic topological insulators.

[1] Lu, L., Joannopoulos, J. D., & Soljačić, M. (2014). Topological photonics. Nature photonics, 8(11), 821.
[2] Christiansen, R., Wang, F., Sigmund, O. & Stobbe, S. (2019). Nanophotonics, 8(8), 1363-1369.
[3] Arora, S., Bauer, T., Parappurath N.,, Barczyk R.,, Verhagen, E., Kuipers L. (2022) arXiv:2202.04402v1 [cond-mat.mes-hall][4] Wu L.-H. and Hu, X. Phys. Rev. Lett. 114, 223901 (2015).
[5] Parappurath, N., Alpeggiani, F., Kuipers, L., & Verhagen, E. (2020). Science Advances, 6(10), eaaw4137.

Plasmon-excited near-field luminescence of semiconductor light sources
Vlastimil Křápek1, Petr Dvořák1, Lukáš Kejík1, Zoltán Édes1, Michal Kvapil1, Michal Horák1, Petr Liška1,
Jan Krpenský1, Tomáš Šikola1
1. Brno University of Technology, Technická 2, CZ-61669 Brno, Czechia
E-mail: krapek@vutbr.cz

On-chip integration of semiconductor light sources is hindered by the fact that the wavelength of the light isconsiderably larger than the physical dimensions of the emitter. Therefore, near-field handling of the emission with adeeply subwavelength spatial resolution would be of great importance. Here we present a fully near-field
photoluminescence study of semiconductor light sources (CdSe/ZnS quantum dots), with a surface plasmon
interference device (SPID) used for the excitation and scanning near-field optical microscopy (SNOM) for thecollection.
The SPID consists of an opaque metallic layer (gold or silver with a thickness of about 200 nm) on a glass substratewith thin slits fabricated using focused-ion-beam milling [1,2,3]. The subwavelength thickness (below 100 nm) of theslits ensures that only surface plasmon polaritons (SPP) can propagate through the slits while the far-field radiation isblocked. The SPID is illuminated from the bottom while the metallic layer blocks the impinging wave. SPP are
generated at the slits, propagate through the slit, and form a standing wave on the top interface, where the distributionof the field is characterized by SNOM. With a semiconductor light source positioned directly at the top interface,luminescence can be generated [Fig. 1(a)]. The luminescence near field at the top of the SPID is again characterized
by a SNOM. The optical signal is collected with the aperture-type probe and guided through the optical fiber to thespectrometer. Details of the setup are provided in Ref. [2].
We have demonstrated the plasmon-excited far-field and near-field luminescence of CdSe/ZnS quantum dots
[Fig. 1(b,c)]. We have observed a rather weak effect of the excitation mechanism on the emission energy and intensity.
This makes the plasmon-excited luminescence a suitable tool for the on-chip integration of semiconductor lightsources, as well as a characterization technique with the subwavelength spatial resolution.

Fig. 1 (a) Scheme and operation principle of SPID. (b) Spatial map of the luminescence from quantum dots excited with SPP. (c)Spectral of the luminescence recorded at selected areas of SPID indicated in panel (b).

References[1] Dvořák P., Neuman T., Břínek L., Šamořil T., Kalousek R., Dub P., Varga P, Šikola T. 2013. Nano Lett., 13, 2558–2563.
[2] Dvořák P., Édes Z., Kvapil M.., Šamořil T., Ligmajer F., Hrtoň M., Kalousek R., Křápek V., Dub P., Spousta J., Varga P, Šikola T. 2017. Opt.
Express, 25, 16560–16573.
[3] Dvořák P., Kvapil M., Bouchal P., Édes Z., Šamořil T., Hrtoň M., Ligmajer F., Křápek V., Šikola T. 2018. Nanoscale, 45, 21363–21368.

Correlative electron and optical spectroscopy of strongly-coupled midinfrared plasmon and phonon polaritons
Pavel Gallina1, Andrea Konečná1, Michal Kvapil1,2, Jiří Liška1,2, Vlastimil Křápek1,2, Radek Kalousek1,2, Juan
Carlos Idrobo3, and Tomáš Šikola1,2
1. CEITEC BUT, Brno University of Technology, Purkyňova 123, 612 00 Brno, Czech Republic
2. Institute of Physical Engineering, Brno University of Technology, Technická 2, 616 69 Brno, Czech Republic
3Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
E-mail: michal.kvapil@ceitec.vutbr.cz

Plasmonic or generally nanophotonic systems have been usually investigated by optical and electron beam
spectroscopic methods. However, as a rule, each of them have been applied for individual samples separately without
direct comparison of their results. In this presentation we take up this challenge and report on the correlative electronand optical spectroscopy applied for an exploration of fundamental phenomena associated with nanostructured systems
possessing both infrared phonon polaritons (PhPs) and plasmon polaritons (PPs). More specifically, we have studied
an electromagnetic coupling between MIR PhPs in a silicon dioxide membrane and low-energy localized surface
plasmon (LSP) modes formed by the confinement of PPs in micrometer-long gold antennas. We have found that farfield IR spectra can be substantially different from EEL spectra, which we confirm by experiments supported bynumerical simulations and analytical modeling. We show that by precisely positioning the electron beam, the coupling
between the polaritonic excitations can selectively trigger either uncoupled PhPs or coupled LSPs/PhPs. Based on our
understanding of the focused-beam excitation of the polaritonic system, we also present a post-processing analysis in
the EEL spectra that facilitates identification of the new hybrid modes and allows an easier comparison to the far-field
optical spectra [1].
In addition to this study, we will present a complementary analysis of the electromagnetic coupling between localized
surface plasmons in gold rectangular antennas and MIR PhPs in a silicon dioxide thin film on a semi-infinite silicon
substrate. Even though the underlying principles in this system have been previously described [2, 3], we complement
these results by a detailed analysis of the resultant hybrid modes based on a coupled oscillator model, realistic SiO2
dielectric function, as well as on the calculation of the Hopfield mixing coefficients [4].

Fig. 1 Coupled system response as a function of the plasmonic antenna length. Simulated pseudo-dispersions for (a) optical scattering and (b)reference-subtracted EEL spectra.

References[1] Gallina, P. et al., arXiv:2112.12832 (2021), https://arxiv.org/pdf/2112.12832.pdf[2] Huck, C; Vogt, J.; Neuman, T.; Nagao, T.; Hillenbrand, R.; Aizpurua, J.; Pucci, A.; and Neubrech, F., Strong coupling between phononpolaritons and plasmonic nanorods, 2016, Opttics express 24, 25528.
[3] Shelton, D.J.; Brener, I.; Ginn, J.C.; Sinclair, M.B.; Peters, D.W.; Coffey, K.R.; and Boreman, G.D., Strong coupling between nanoscale
metamaterials and phonons, 2011, Nano letters 11, 2104.
[4] Gallina P. et al., arXiv:2112.07767v1 (2021), https://arxiv.org/pdf/2112.07767.pdf

Far-field photonic spin texture of thermal radiation from a non-isothermal
nano-antenna
Parry Y. Chen1, Roy Ayash1, Chinmay Khandekar2, Yonatan Sivan1, Z. Jacob2
1. School of Electrical and Computer Engineering, Ben-Gurion University; 2. School of Electrical and Computer Engineering, Purdue University
E-mail: zjresearchgroup@gmail.com

The fluctuational electrodynamic analysis of thermal radiation from non-equilibrium or non-isothermal
bodies remains largely unexplored because it is computationally cumbersome due to the requirement of volume
integration over the fluctuating currents inside the emitter. Here, we put forth a formalism combining fast calculations
based on complex permittivity mode expansion (also known as generalized normal modal expansion, GENOME) [1]and fluctuational electrodynamics to accelerate research at this frontier. Our formulation enables a completecharacterization of the emission which for systems with a uniform temperature, require only knowledge of thepermittivity eigen modes and eigenfunctions, thus, making our approach significantly simpler and accurate than any
previous approach.
We then employ our formalism to predict that temperature gradients in an experimentally relevant long silica
wire can generate thermal emission with a non-zero spin that extends into the far-field, is constant in direction andsign, and is perpendicular to the direction of power flow [2]. Such nonequilibrium spin texture of heat radiation is nonintuitive and quite unexpected since the previously known origins of spin emission rely on the use of exotic chiral,
nonisotropic or magnetic materials, mechanical rotations or magnetic fields and is limited to the near-field.

Fig. 1 (Left) An example geometry that can be treated by our formalism for non-equilibrium fluctuation electrodynamics. A temperature gradient ismaintained across the cross-section of a circular silica rod, which extends infinitely along the z-direction. Heat flux, characterized by Poynting's
vector, is generated along the radial direction. More notably, spin fields are generated that are in-plane, characterized by a spin vector which isperpendicular to both the plane and the Poynting vector. (Right) The spin extends into the far-field, D >> r, where r is the radius of the cylinder andD is the radius of the far-field contour. The normalized spin converges to the displayed non-zero values. The sign and the magnitude of the far-field
spin vector changes as a function of the in-plane polar angle, but does not substantially change at scales of the order of the wavelength.

References[1] Chen, P. Y., Bergman, D. J., Sivan, Y., (2019), Phys. Rev. Appl. 11, 044018.
[2] Chen, P. Y., Ayash, R., Khandekar, C., Jacob, Z., Sivan, Y., (2022), submitted.

Optical phase control in strongly driven infrared nanoresonators assisted
by molecular vibrations
Felipe Herrera1,2, Mauricio Arias3, Johan F. Triana1
1. Departamento de Física, Universidad de Santiago de Chile, Santiago, Chile
2. ANID-Millennium Institute for Research in Optics, Chile
3. Departamento de Física, Universidad de Concepción, Concepción, Chile
E-mail: felipe.herrera.u@usach.clOpen infrared nanoresonators are ideal platforms for studying room temperature cavity QED with organic
materials. Nanotips can be used for imaging the coupled near field with a spatio-temporal resolution that is currently
unavailable with conventional diffraction-limited cavities [1]. We propose and numerically demonstrate a novel typeof ultrafast infrared blockade effect assisted by molecular vibrations that can be used for manipulating the temporal
response of pulse-driven vibration-resonator systems. Using strong femtosecond infrared pulses, near-field IR photons
and molecular vibrations become transiently detuned due to the natural anharmonicity of higher vibrational levels.
This effective vibrational blockade imprints a coherent phase shift on the free induction decay signal that can bemeasured using tip nanoprobes. We predict infrared phase shifts of a few radians with short (~100 fs) pulses that canbleach the vibrational ground state by 10% or more. The phase shift depends nonlinearly with the pulse power [2]. In
contrast with other blockade mechanisms in cavity QED, our scheme does not rely on light-matter entanglement andis suitable for weak coupling scenarios. Possible applications in optical state preparation in the mid-infrared are
discussed.
References[1] B. Metzger, E. Muller, J. Nishida, B. Pollard, M. Hentschel, and M. B. Raschke. 2019. Phys. Rev. Lett. 123, 153001[2] J.F. Triana, M. Arias, F. Herrera et. Al. 2021. arXiv:2110.07371.

Compact 750-µJ, 75-W, sub-40-fs laser for efficient THz light sources
driven by a two-color scheme
Christian Grebing1, Fabian Stutzki1, Sven Breitkopf1, Oliver Herrfurth1
Joachim Buldt2, Tino Eidam1,* and Jens Limpert1,2,3,4
1. Active Fiber Systems GmbH, Ernst-Ruska-Ring 17, 07745 Jena, Germany.
2. Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Albert-Einstein-Str. 15, Germany.
3. Fraunhofer Institute for Applied Optics and Precision Engineering, Albert-Einstein-Str. 7, 07745 Jena, Germany
4. Helmholtz-Institute Jena, Fröbelstieg 3, 07743 Jena, Germany
Author e-mail address: publications@afs-jena.de

The THz spectral range attracted a lot of interest during recent years due to the growing number of applications invarious fields including fundamental research [1], material research [2], imaging [3] or quality control [4] in production
processes. For many of these applications, more output power of the THz source is demanded. In principle, this needcan be satisfied by higher input power of the driving light source, however, it is often limited by the damage thresholdof the THz-generation material. This can be circumvented when gas-based THz generation in a plasma is utilized [5].
In this contribution, we present a state-of-the-art ultrafast fiber-based chirped-pulse amplifier (FCPA) systememitting 800µJ laser pulse at 1030 nm wavelength and 100kHz repetition rate to drive a THz-generation scheme as
depicted in Figure 1.

Figure 1: Schematic view of the laser-based THz generation as published in reference [5].
The FCPA is used to drive a multipass cell (MPC) that enables efficient pulse compression to sub-40-fs pulse
duration. More than 90% of the input laser power is preserved during compression due to our recent advances in
multipass cells [6]. The MPC enables pulse compression to less than 40fs as shown by the autocorrelation signal in
Figure 2 (left). The compressed pulses are then used for second-harmonic generation. Both the fundamental mode andits second harmonic can then be focussed into gas for plasma-based THz generation. The presented THz-driver source
features excellent long-term power stability over more than 8 hours at 75W average power with 0.2% standard
deviation as depicted in Figure 2 (right).

Figure 2: (left) Autocorrelation measurement (solid line) and sech2 fit (dashed line) of the compressed laser
pulses featuring 32 fs pulse duration at 75W average power. (right) Corresponding long-term power-stability
measurement of the compressed laser pulses over more than 8 hours.
References[1] O. Schubert et al., “Sub-cycle control of terahertz high-harmonic generation by dynamical bloch oscillations”,
Nat. Photonics 8, 119–123 (2014)[2] Daniele Nicoletti and Andrea Cavalleri, "Nonlinear light–matter interaction at terahertz frequencies," Adv. Opt. Photon. 8, 401-464 (2016)[3] C. Jansen et al., “Terahertz imaging: applications and perspectives,” Appl. Opt. 49 19, E48–E57 (2010).
[4] M. Tonouchi, Cutting-edge terahertz technology. Nat. Photonics 1, 97–105 (2007)[5] J. Buldt et al., “Gas-plasma-based generation of broadband terahertz radiation with 640 mW average power”, Opt. Lett. 46, 20 (2021).
[6] C. Grebing et al., “Kilowatt-average-power compression of millijoule pulses in a gas-filled multi-pass cell”, Opt. Lett. 45, 22 (2020).

Time-resolved Cathodoluminescence in a TEM
S. Meuret*1, L. H.G. Tizei2, F. Houdellier1, S. Weber1, Y. Auad2, M. Tencé2, H.-C. Chang3, M. Kociak2 and A.
Arbouet1
1 - CEMES-CNRS Université de Toulouse 29 rue Jeanne Marvig 31055 Toulouse France
2 - Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405, Orsay, France
3 - Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan*sophie.meuret@cemes.fr
Cathodoluminescence is the emission of visible light when an electron interacts with matter. It is a powerful techniqueto study the luminescence properties of semiconductors below the diffraction limit of visible light. The developmentof time-resolved Cathodoluminescence (TR-CL) in a scanning electron microscope (SEM) enabled the measurementof the lifetime of excited states in semiconductors with a sub-wavelength spatial resolution. It was used for example
to measure the influence of stacking faults on the GaN exciton lifetime [1], to probe the role of a silver layer on the
dynamics of a YAG crystal [2] or to show the influence of stress on the optical properties of ZnO nanowires [3]. These
results demonstrate that TR-CL is essential to study the correlation between semiconductor optical and structuralproperties (composition, defects, strain…). Despite giving precious information, TR-CL in a SEM is still limited inspatial resolution. CL in the transmission electron microscope (TEM) could dramatically improve the spatial resolution
with respect to SEM-CL, in addition to give access to multiple complementary analysis tools (from atomic scale
imaging to electron energy loss spectroscopy).
In this presentation, we will discuss the first experimental demonstration of time-resolved cathodoluminescence withina TEM [4]. It was performed in a unique femtosecond pulsed TEM, with a cold-FEG electron gun [5]. This technology
allows among other things sub-ps temporal resolution while preserving a spatial resolution of a few nanometers,
essential for the study of nanophotonic materials. We will present the first lifetime maps acquired in a TEM both on
nano-diamonds and InGaN quantum wells and discuss the unique features and opportunities of this technique.

Figure 1: a) TEM image of a nano-diamond cluster containing a high density of nitrogen vacancy color center. b) CL Intensitymap (whit square in a). c) Lifetime extracted from the decay trace at each pixel. d) Example of two decay traces form two
different pixels.
References
[1]
[2]
[3]
[4]
[5]

P. Corfdir et al., “Exciton localization on basal stacking faults in a-plane epitaxial lateral overgrown GaN grown by hydride vapor phase
epitaxy,” J. Appl. Phys., vol. 105, no. 4, p. 043102, 2009.
R. J. Moerland, I. G. C. Weppelman, M. W. H. Garming, P. Kruit, and J. P. Hoogenboom, “Time-resolved cathodoluminescencemicroscopy with sub-nanosecond beam blanking for direct evaluation of the local density of states,” Opt. Express, vol. 24, no. 21, p.
24760, 2016.
X. Fu et al., “Exciton Drift in Semiconductors under Uniform Strain Gradients: Application to Bent ZnO Microwires,” ACS Nano, vol.
8, no. 4, pp. 3412–3420, 2014.
S. Meuret et al., “Time-resolved cathodoluminescence in an ultrafast transmission electron microscope,” Appl. Phys. Lett., vol. 119, no.
6, p. 6, 2021.
F. Houdellier, G. M. Caruso, S. Weber, M. Kociak, and A. Arbouet, “Development of a high brightness ultrafast Transmission Electron
Microscope based on a laser-driven cold field emission source,” Ultramicroscopy, vol. 186, pp. 128–138, 2018.

Slot-bridge nanobeam cavities for high Q/V ratios
Joshua Fabian1,2, Xiruo Yan1,3, Adan Azem1,2, Donald Witt1,2, Kashif Awan1, Matthew Mitchell1,
Andreas Pfenning1, Lukas Chrostowski1,2, and Jeff F. Young1,3
1. Steward Blusson Quantum Matter Institute, University of British Columbia, 2355 East Mall, Vancouver, BC V6T 1Z4, Canada
2. Department of Electrical and Computer Engineering, University of British Columbia, 5500-2332 Main Mall, Vancouver, BC V6T 1Z4,
Canada3. Department of Physics and Astronomy, University of British Columbia, 325-6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
E-mail: jfabian@ece.ubc.ca

Optical resonators that enhance the coupling between individual optically active elements and photonic modes area central element in quantum information technologies based on spin-photon interactions, see Refs. [1-4]. These
resonators should simultaneously have low losses (i.e., a high Q factor) and a small optical mode volume (to increase
the coupling strength). Based on a design proposal by Choi et al. [5], we demonstrate a silicon photonic crystal
nanobeam cavity that provides extreme dielectric light confinement within a tiny bridge structure with a mode volume
down to 𝑉𝑉 ≈ 0.0093 𝜆𝜆30 while keeping a high quality factor of 𝑄𝑄 ≈ 15 k.

Figure 1 (a) shows a SEM image of the fully under-etched cavity. From the SEM images, we extract the exact
device dimensions such as a bridge width of only 45 nm (indicated by a white arrow). Based on the experimentally
determined device dimensions, we have calculated the mode profiles for the lowest three supported resonant modes
using a three-dimensional finite difference time domain (3D-FDTD) solver. The simulated mode volumes for the first,
second, and third order mode are found to be 𝑉𝑉1 ≈ 0.0093 𝜆𝜆30 , 𝑉𝑉2 ≈ 0.0092 𝜆𝜆30 , and 𝑉𝑉3 ≈ 0.011 𝜆𝜆30 , respectively, andare also shown in Figure 1 (a). The first order mode is particularly well suited for enhanced coupling schemes due toits field maximum which is strongly localized within the bridge area. Figure 1 (b) shows the measured transmission
spectrum with a closer view of the first order mode in linear scale. The second order mode is strongly damped by thegrating couplers used to couple light into the chip, whereas the third order mode is completely suppressed. Using a
Lorentzian fit function, we extract 𝑄𝑄1 ≈ 15 k, and 𝑄𝑄2 ≈ 3 k, respectively.

Fig. 1. (a) SEM image of the fabricated slot-bridge nanobeam cavity and simulated mode profiles of the lowest 3 supported
modes. The cavity is formed by holes in a free-floating silicon nanobeam with a slot connecting the two innermost holes.
The bridge (indicated by a white arrow) spans the slot at the center of the cavity and has a width of 45 nm. The simulated
mode volumes are 𝑉𝑉1 ≈ 0.0093 𝜆𝜆30, 𝑉𝑉2 ≈ 0.0092 𝜆𝜆30, and 𝑉𝑉3 ≈ 0.011 𝜆𝜆30, respectively. (b) Measured transmission spectrumwith zoom-in on the first order mode in linear scale. The Lorentz peak fit yields a high quality factor of 15 k at a wavelengthof 1565.2 nm. The second and third order mode are suppressed by the grating coupler used to couple light into the chip.

References[1] Nemoto, K. et al. 2014. Phys. Rev. X 4, 031022.
[2] Morse, K. J. et al. 2017. Sci. Adv. 3, e1700930.
[3] Yan, X. et al. 2020. Adv Quantum Tech 3, 2000011.
[4] Yan, X. et al. 2021. APL Photonics 6, 070901.
[5] Choi, H., Heuck, M. & Englund, D. 2017. Phys. Rev. Lett. 118, 223605.

iSCAT in Nanofluidic Channels: A Physical Model
Philippe Marc Nicollier 1, Armin Knoll1
1. IBM Research Europe - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
E-mail: phn@zurich.ibm.com

Interferometric Scattering Microscopy (iSCAT) has emerged in the last 20 years as a method of choice to achievelabel-free, high-speed imaging and characterization of nanoparticles [1]. The interferometric nature of the techniqueleads to a favorable scaling of contrast with particle volume. The contrast depends linearly on the scattered andreference field amplitudes |Es| and |Er|, as well as on their phase difference θ:
C≈

|𝐸𝑠|
|𝐸𝑟|

cosθ

To reach sensitivities and signal-to-noise ratios necessary to visualize biological species such as single proteins [2],optimized set-ups and image processing procedures have been implemented. Among them, particles are generally
immobilized on the coverslip interface to provide a defined focal plane and to allow for frame averaging. However, it
is also desirable to image freely diffusing particles in nanofluidic channels [3]. Many parameters play a role when
imaging diffusing particles in nanofluidic channels, such as the geometry of the slits, the thin film structure of theconfining walls, the position of the particle in the gap, as well as the focus position of the imaging beam [4]. It is thus
crucial to have a robust description of the imaging contrast to be expected for a particular particle in a certain
nanofluidic channel geometry.
Various models have been proposed in the last years to describe the contrast and point spread function in iSCAT
imaging [5-8]. However, a comprehensive physical model taking into account near-field effects, as well as considering
the presence of multiple dielectric interfaces, is yet to be published.
Building on existing models, we propose a physical description of the interference contrast and point spreadfunction for the general case of diffusing particles in multilayered nanofluidic slits. We are in the process of validating
the simulations with experimental data acquired on our dedicated experimental set-up, the nanofluidic confinement
apparatus (NCA) [9]. The NCA allows us to perform experiments in nanofluidic gaps of varying wall composition,
gaps and focal positions. Thus, we can explore a wide parameter space to validate the model. This will allow us topredict the optimal imaging contrast as a function of layer parameters and illumination conditions.
References[1] Young, G., Kukura, P., 2019, Ann. Rev. Phys. Chem., 70, 301-322[2] Piliarik, M., Sandoghdar, V., Nat. Comm., 2014, 5, 4495, 1-8[3] Spackova et al., Nat. Methods, 2022, 1-8[4] Mojarad, N., Sandoghdar, V., Krishnan, M., Opt. Exp., 2013, 21, 8, 9377-9389[5] Fringes, S., Skaug, M., Knoll, A., J. Appl. Phys., 2016, 119, 2, 024303[6] Sevenler, D., Avci, O., Ünlü, S., Biomed. Opt. Exp., 2017, 8, 6, 2976-2989[7] Mahmoodabadi, R., et al., Opt. Exp., 2020, 28, 18, 25969-25988[8] He, Y., et al., J. Phys. D.: Appl. Phys. 2021, 54, 274002[9] Fringes, S., Holzner, F., Knoll, A., Beilstein J. Nanotech., 2016, 9, 1, 301-310

iSCAT Microscopy for Imaging the Interactions of Polymer Dots with HeLa
Cells
Eric Boateng, Bruno Luppi, William Primrose, Luke Melo, Zachary Hudson, and Edward Grant
Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1 Canada
eboateng@chem.ubc.ca

Semiconducting polymer dots (Pdots) have emerged as powerful nanoscale probes forbioimaging, sensing, and photodynamic therapy. Characterized by high brightness, resistance tophotobleaching, and tunable surface chemistry, Pdots can enable imaging and analysis on the scaleof single nanoparticles. Pdots are water-dispersed nanoparticles composed of >50% organic
semiconducting polymer, ideally with strong absorbance and high emission quantum yield [1–3].
Here we aim to image the biological effects of Pdot-cell interactions using interferometricscattering (iSCAT) microscopy. We have studied the iSCAT kinetics of diblock copolymer
nanoparticles composed of a water-soluble polyethylene glycol-based block and a rigid organic
semiconductor block.
Initial experiments have applied the methodologies we have developed to gauge size
distributions of gold nanoparticles [4] to record iSCAT mass photometry signals from HeLa cells
and pure Pdots in aqueous suspension. These Pdots had an estimated mean diameter of 100 nm,
with a standard deviation σ of about 30 nm. HeLa cells were incubated at 37°C and maintained ina cell medium until imaging. Figure 1A is an iSCAT image of individual HeLa cells attached onpoly-D-lysine (PDL) derivatized glass coverslip. Figure 1C shows a single frame of a typicalratiometric image of Pdots landing on the PDL coverslip. A comparison in Figure 1D shows thechanges in the HeLa cell image when altered by interaction with Pdots. This observation is a typicalmechanism of cell lysis recorded when HeLa cells take up polymer nanoparticles.

Fig. 1. (A) iSCAT image of single HeLa cells. (B) Close-up view of the HeLa cell showing very well-resolved membrane as the
specific site for Pdots penetration. (C) Ratiometric image of polymer dots landing on a poly-D-lysine coverslip recorded at a single
frame. (D) Changes in HeLa cell image observed when polymer dots penetrate. This shows a typical mechanism of cell lysis, redarrows indicate remains of the cell-penetrating polymer dots in the host cell.

References[1] Rong, Y et al. 2013. Multicolor Fluorescent Semiconducting Polymer Dots with Narrow Emissions and High Brightness. ACS Nano, 7 (1),376–384.
[2] Yuan, Y.; Hou, W.; Qin, W.; Wu, C. 2021. Recent Advances in Semiconducting Polymer Dots as Optical Probes for Biosensing. Biomaterial.
Science 9:328-346[3] Christopherson C.J.; Paisley N.R.; Xiao Z.; Algar, W.R.; Hudson, Z.M. 2021. Red-Emissive Cell-Penetrating Polymer Dots Exhibiting
Thermally Activated Delayed Fluorescence for Cellular Imaging. Jam. Chem. Soc. 143:13342-9.
[4] Melo, L.; Hui, A.; Kowal, M.; Boateng, E.; Poursorkh, Z.; Rocheron, E.; Wong, J.; Christy, A.; Grant, E. 2021. Size distributions of colloidal
gold nanoparticles measured in solution by single-particle mass photometry. J. Phys. Chem. B, 125:12466−12475

iSCAT as a high-throughput, accurate and reproducible probe of size distribution insolution-phase suspensions of cellulose nanocrystals
Hooman Tavakolizadeh,1 Mahfuzul Hoque,2 Luke Melo,1 Johan Foster2 and Edward Grant1
1
Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
E-mail: hooman.tzn@gmail.com

2

The innovative use of nanocellulose materials (NCMs) and cellulose nanocrystals (CNCs) inparticular, calls for readily applicable methods that can characterize morphology and size
distributions, as well as dispersion-agglomeration state in solution. Transmission electron (TEM)
and atomic force (AFM) microscopy yield structurally detailed fixed images, but require lowthroughput, labor-intensive processes of analysis that are prone to inconsistency [1,2]. Dynamic
light scattering (DLS) operates on solution-phase dispersions, but suffers well-known limitationsin accuracy and dynamic range.
Interferometric scattering microscopy (iSCAT) offers a direct high-throughput means of sampling
nanoparticles from solution [3]. In this technique, the light scattered by every particle as it binds
to a coverslip interferes with a reflected reference field to form a diffraction-limited image with acontrast that scales linearly with the mass of the particle. Here, we demonstrate the application ofiSCAT to measure the size distribution of CNCs with a throughput as high as 1,000 particles per
minute.
Figure 1(a) shows one frame in a sequence of ratiometric images. Particles that appear as pointspread functions in Figure 1(a) fade to one as the background advances to include them. Figure1(b) shows the distribution of contrast formed by the measurement of 2574 particles in a 3 minuteexperiment. The particle size distribution derived from many TEM images such as Figure 1(c)calibrates contrast to determine the CNC mass distribution.
(a)

(b)

(c)

Figure 1 (a) Ratiometric iSCAT image of single CNCs landing and receding into the background. (b) Distributionof contrast for 2574 particles acquired in a 3 minute experiment. (c) TEM micrograph of CNCs.

References[1] Balea, A., Blanco, A., Delgado-Aguilar, M., Monte, M., Tarres, Q., Fuente, E., Mutje, P., & Negro, C. 2021. BioResources, 16(2), 4382-4410[2] Foster J, Moon RJ, Agarwal UP, Bortner MJ, Bras J, et al. 2018. Chem. Soc. Rev.,47, 2609-2679[3] Melo L, Hui A, Kowal M, Boateng E, Poursorkh Z, Rocheron E, et al. 2021. J Phys Chem B, 125(45):12466-12475.

The Solution Transport Limit of Non-Langmuir iSCAT Adsorption
Edène Rocheron1, Luke Melo1, Jake Wong1, Edward Grant1
1. University of British Columbia, Department of Chemistry, 2036 Main Mall, Vancouver, BC, Canada, V6T 1Z1
E-mail: lmelo@chem.ubc.ca

Specialized applications of nanoparticles often call for particular, well-characterized particle
size distributions in solution, but this property can prove difficult to measure. Recent work has
exploited interferometric scattering (iSCAT) mass photometry advantages of high-throughput andlarge dynamic range to quickly infer size distributions in colloidal suspensions of gold
nanoparticles [1]. Other applications have measured the kinetics of binding reactions to gauge theconcentration of reactants in solution [2]. The most straightforward analysis of experimental
measurements assumes in both cases that the rate of transport in the bulk exceeds the depletion ofparticles in the solution immediately adjacent to the plane of measurement.
We have found evidence for 5, 10 and 15 nm gold nanoparticles that the observed rate of binding
to a poly-D-lysine coated coverslip decreases much faster than deposition decreases the bulk
concentration of nanoparticles in solution [3]. The fall-off in deposition rate clearly fails to
conform with a Langmuir adsorption model. The evident size selectivity of this non-Langmuir
behaviour seems to suggest a deposition process that is limited by the transport properties ofnanoparticles in quiescent solutions.
We computationally model the molecular dynamics of 10 nm gold nanoparticles in solution to
track concentration as a function of distance from the coverslip at observed deposition rates forreasonable values of diffusion coefficient. Our results indicate the formation of a depletion layer
above the surface of the coverslip, creating a concentration gradient that grows with time. (Fig.
1A). Particles that remain in solution when the rate plateaus remain available to replenish thedeposition when we stir the solution. (Fig. 1B)

Fig. 1 (A) As time progresses, the depletion of particle concentration rises through the height of the bulk. (B) As time progresses, the rate ofdeposition decreases. However, upon stirring the solution, the deposition rate increases again corresponding to a replenished depletion layer.

References[1] Young, G., Hundt, N., Cole, D., Fineberg, A., Andrecka, J., Tyler, A., Olerinyova, A., Ansari, A., Marklund, E. G., Collier, M. P., Chandler, S.
A., Tkachenko, O., Allen, J., Crispin, M., Billington, N., Takagi, Y., Sellers, J. R., Eichmann, C., Selenko, P., … Kukura, P. (2018). Quantitative
mass imaging of single biological macromolecules. Science, 360(6387), 423–427.
[2] Young, G., & Kukura, P. (2019). Interferometric Scattering Microscopy. Annual Review of Physical Chemistry, 70(1), 301–322.
[3] Melo, L., Hui, A., Kowal, M., Boateng, E., Poursorkh, Z., Rocheron, E., Wong, J., Christy, A., & Grant, E. (2021). Size Distributions of Gold
Nanoparticles in Solution Measured by Single-Particle Mass Photometry. Journal of Physical Chemistry B, 125(45), 12466–12475.

Detection of Nanoplastics in Mixed Solutions using Interferometric Scattering
Microcopy
Matthew D. Kowal, Teresa M. Seifried and Edward Grant

Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1
E-mail: mdkowal@chem.ubc.ca

Synthetic polymers, produced and discarded for nearly a century, ultimately degrade to form small plastic
particles now found in every sphere of the environment. Measurements have detected evidence for airborne
microplastics in Arctic and Antarctic snow [1]. Microplastic discharged from terrestrial sources pollute natural
aquatic environments in all parts of the world [2].
Accurate assessments of the extent of microplastic pollution face a number of fundamental materials
challenges. Real environmental systems contain natural particulate matter in abundance. Assays must distinguishmicroplastics from mineral dust and natural organic particles. Microplastics span a very broad distribution in size,
from tens of millimeters to tens of nanometers. Though rarely detected, particles at the small end of this range
dominate in number, and may well present the greatest cause for pathological concern [3].
Here we describe an approach using interference microscopy to count individual nanoplastic particles as theyland and bind to poly-D-lysine and other derivatized coverslips. Small plastic particles generally support a negative
surface charge at near-neutral pH [4]. Microplastic zeta potentials generally exceed those of mineral particles [5].
Thus, conditions exist under which functionalized coverslips can differentially bind suspended microplastics, enabling
methods of iSCAT microscopy to measure abundance and relative size [6].

Fig. 1 Left, Interferometric scattering images of polystyrene nanobeads in (A) 50 nm, (B) 100 nm, C) 200 nmm D) 350 nm
diameters. Scale bar: 2 µm. Right, 3D model of the microscope sample stage

References[1] Aves AR, Revell LE, Gaw S, Ruffell H, Schuddeboom A, Wotherspoon NE, LaRue M, McDonald AJ. First evidence of microplastics in
Antarctic snow. The Cryosphere Discussions. 2022 Jan 4:1-31.
[2] Bergmann M, Gutow L, Klages M. Marine anthropogenic litter. Springer Nature; 2015.
[3] Lim X. Microplastics are everywhere—but are they harmful?, Nature 2021 593, 22-25[4] Wang Y, Xu L, Chen H, Zhang M. Retention and transport behavior of microplastic particles in water-saturated porous media. Science of The
Total Environment. 2022 808 152154.
[5] Berg JM, Romoser A, Banerjee N, Zebda R, Sayes CM. The relationship between pH and zeta potential of∼ 30 nm metal oxide nanoparticle
suspensions relevant to in vitro toxicological evaluations. Nanotoxicology. 2009 1 276-83.
[6] Melo, L., Hui, A., Kowal, M., Boateng, E., Poursorkh, Z., Rocheron, E., Wong, J., Size Distributions of Gold Nanoparticles in Solution
Measured by Single-Particle Mass Photometry, The Journal of Physical Chemistry B 2021, 125 12466-12475

High-throughput synthesis and characterization of compositionally-graded films
Shahram Moradi1, Makhsud Saidaminov1,2

1. Department of Electrical & Computer Engineering, University of Victoria, 3800 Finnerty Rd, Victoria, BC V8P 5C2, Canada
2. Department of Chemistry, University of Victoria, 3800 Finnerty Rd, Victoria, BC V8P 5C2, Canada
E-mails: msaidaminov@uvi.ca
Shahrammoradi@uvic.ca

New materials are conventionally searched by synthesizing and studying a limited number of compositions. However,this approach is fragmentary and unfortunately misses a significant fraction of material alloys. This fragmentary approach
my delay or even disable the discovery of potential ‘magic’ compositions.
Here we report a method for fabricating compositionally gradient films to synthesize all possible alloys from binary
systems in a single shot in less than 1 min. We use our approach to study an applied challenge – the stability of halide
perovskites, a promising and fast-growing class of semiconductors for various optoelectronic applications. We synthesize
over 200 possible phases from a binary system of MAPbI3 and MAPbBr3, and then study their optical properties in ahigh-throughput manner (Fig. 1). We find that perovskite alloys experience three different degradation mechanisms
depending on halogen content: Br-rich perovskites degrade through hydration, while I-rich perovskites – through the lossof organic component; all other intermediate alloys degrade through segregation to Br-rich perovskite and lead iodide.
The proposed method of fabricating composition gradient film paves avenues for discovering new materials andprocessing parameters for a broad range of applications that rely on compositional engineering.

Fig. 1 Optical properties of MAPb(IxBr1-x)3

References[1] S. Moradi et. al. “High-throughput exploration of halide perovskite compositionally-graded films and degradation mechanisms”, Just
acceptedCommunications Materials.

Defocus Phase Contrast in Photon-Induced Near-field Electron Microscopy
John H. Gaida1,2, Hugo Lourenco-Martins1,2, Sergey V. Yalunin1,2, Armin Feist1,2, Murat Sivis1,2,
Thorsten Hohage3, F. Javier García de Abajo4,5, and Claus Ropers1,2
1. Max Planck Institute for Multidisciplinary Sciences, Am Faßberg 11, 37077 Göttingen, Germany
2. 4th Physical Institute, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
3. Institute of Numerical and Applied Mathematics, University of Göttingen, Lotzestraße 16-18, 37083 Göttingen, Germany
4. ICFO-Institut de Ciencies Fotoniques, Av. Carl Friedrich Gauss, 308860 Castelldefels (Barcelona), Spain
5. ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spainjohn.gaida@mpinat.mpg.de

Electron microscopy encompasses a variety of techniques to study the nanoscale optical properties of materials anddevices. Spontaneous inelastic electron-light scattering (IELS), resulting in cathodoluminescence and electron-energy
loss, is frequently used to spectroscopically characterize the photonic density of states with high spatial resolution overa broad optical bandwidth [1]. In addition, stimulated scattering in the presence of optical illumination of the sample,
allows for mode- and polarization-selective quantitative measurements of optical near fields in the form of PhotonInduced Near-field Electron Microscopy (PINEM) [2, 3]. In this technique, inelastic scattering produces sidebands inthe electron kinetic energy spectrum corresponding to energy gains and losses in multiples of the photon energy. The
number of populated sidebands is a direct measure of the near-field strength [1], and since the scattering process iscoherent in nature, the spatial distribution of the optical near-field phase is imprinted onto the electron wave function.
Here, we use Fresnel-mode defocus imaging to reveal electron phase contrast induced by stimulated IELS.

Fig. 1 a, Sketch of the PINEM experiment with IELS and energy-filtered imaging. b, Schematic of Fresnel microscopy. c, EFTEM
micrographs reveal the amplitude and deflections of the optical near-field under in-focus and overfocus imaging conditions,
respectively. d, Simulated amplitude and phase of the near-field interaction 𝑔𝑔 and resulting in focus and overfocus EFTEM images.

The experiments are carried out at the Göttingen Ultrafast Transmission Electron Microscope (UTEM) operated
with a laser-triggered field emission electron gun delivering electron pulses of high spatial coherence. Here, a gold
nanotip is excited by femtosecond laser pulses shown in Fig. 1 a. Collimated electron pulses are used for PINEM,
imaging individual sideband amplitudes of the electron wave function Ψ𝑁𝑁 (𝑁𝑁 photon order). To this end, we employ asingle-electron-sensitive detector behind an imaging electron spectrometer with a controllable slit for energy selection.
Figure 1 c presents an in-focus image collected from all electrons experiencing energy loss, exhibiting the shadow
image of the nanotip and a standing wave pattern resulting from interference between surface plasmons excited on theconical tip and far-field radiation scattered at the tip-supporting shaft. A corresponding simulation of the near-fieldinteraction near the tip apex is displayed in Fig. 1 d and shows general agreement. In the absence of aberrations, theimage intensity in focus is independent of the phase of the coupling parameter 𝑔𝑔. However, gradients in the phase of
𝑔𝑔 result in electron beam deflections, which can be revealed using phase-contrast imaging. Specifically, we employ
Fresnel-mode Lorentz imaging, a phase-contrast technique that is widely used to characterize in-plane magnetic fields.
As illustrated in Fig. 1 b, defocus imaging translates locally varying beam deflections into amplitude modulations. In
the specific geometry in study, strong phase gradients are induced near the apex of the tip (cf. simulation of phasegradients in Fig. 1 d, center). Working under overfocus conditions modifies the energy-filtered image, producing abright spot of enhanced intensity near the tip apex, and caustics along the shaft in both experiment (Fig. 1 c, bottom)
and simulation (Fig. 1 d, bottom). In the presentation, we will compare differences in imaging contrast using energy
gain and loss sidebands, coupled by the relation Ψ−𝑁𝑁 = Ψ𝑁𝑁 and, thus, exhibiting opposite deflections and phasegradients. Moreover, we will explore algorithmic near-field phase reconstruction and polarization-dependent imaging.
References[1] García de Abajo, F. J. and Kociak, M. Phys. Rev. Lett. 100, 106804 (2008).
[2] Barwick, B., Flannigan, D. J. & Zewail, A. H. Nature 462, 902–906 (2009).
[3] Harvey, T. R. et al. Nano Lett. 20, 4377–4383 (2020).

Photon pair directly produced into the guided modes ofnonlinear waveguides via down-conversion
Álvaro Rodríguez Echarri1, Joel D. Cox2,3 and F. Javier García de Abajo1,4

1. ICFO – Institut de ciències fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
2. Center for Nano Optics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
3. Danish Institute for Advanced Study, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
4. ICREA – Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spainalvaro.rodriguez@icfo.eu

During the last decades great advances have been made to consolidate the field of quantum communications, in which
the entanglement of particles and photons plays a key role. Up until now, there have been many strategies proposedto generate entangled photon pairs that encode the information carried by photons in their polarization or orbital
angular momentum degrees of freedom. However, additional difficulties are found to steer and manipulate thegenerated photons to use them in practical applications, and therefore efforts have been made to integrate on-chipsources of entangled photons. In this work, we introduce a direct illumination scheme to generate entangled photons
encoded in the optical mode states of a lossless fiber [1] (see Fig. 1a). We study this scheme of pair production by
employing a rigorous theoretical method to down-convert a direct incident electric field into guided modes, whereenergy and momentum conservation restricts the allowed excited modes (see Fig. 1b). In order to quantify the
production rate, we compute the reverse process of frequency sum for which two photons up-convert and emit into
the far field, and based on the reciprocity theorem, both processes have the same probability. We demonstrate thatfor optical fibers made of a suitable nonlinear material such as LiNbO3, the rate of photon pair production can be ~105
under attainable illumination condition, thus supporting the feasibility of this disruptive approach to directly generateentangled and waveguided photon pairs. We thus envision that these findings can stimulate experimental ventures inquantum optics to entangle light with a predictable degree of fidelity and help alleviate practical issues related to thecoupling of quantum light sources to optical components required in emerging quantum information technologies.

Figure 1. Generation of waveguided entangled photon pairs by down-conversion in an optical fiber. (a)Illustration of a cylindrical fiber (radius 𝒂𝒂, material permittivity 𝝐𝝐𝟏𝟏 , host permittivity 𝝐𝝐𝒉𝒉 ) subject to normal
illumination. Each incident photon can be down-converted via the second-order nonlinear response of the fiber
material (susceptibility 𝝌𝝌(𝟐𝟐) ) to produce two waveguided photons within modes 𝒊𝒊 and 𝒊𝒊′ of fields 𝐄𝐄𝒊𝒊 and 𝐄𝐄𝒊𝒊′ ,frequencies 𝝎𝝎𝒊𝒊 and 𝝎𝝎𝒊𝒊′ , and wave vectors 𝒒𝒒𝒊𝒊 and 𝒒𝒒𝒊𝒊′ satisfying 𝒒𝒒𝒊𝒊 + 𝒒𝒒𝒊𝒊′ = 𝟎𝟎. (b) Dispersion diagram of waveguidemodes (normalized frequency 𝝎𝝎𝝎𝝎/𝒄𝒄 as a function of normalized wave vector 𝒒𝒒𝒒𝒒) for 𝝐𝝐𝟏𝟏 = 𝟓𝟓 and 𝝐𝝐𝒉𝒉 = 𝟏𝟏. The light
cones in the waveguide and host materials (white and grey areas, respectively) limit the existence of the modes. We
highlight the two lowest-order modes that possess nonzero longitudinal field components (𝐇𝐇𝐇𝐇𝟏𝟏𝟏𝟏 and 𝐓𝐓𝐓𝐓𝟎𝟎𝟎𝟎 , see labels)
and enable down-conversion with a small number of emission photon-pair channels: one symmetric (yellow circles)
and two asymmetric (blue and green circles) channels. (c) Detail of these channels, showing the threshold frequencyof the 𝐓𝐓𝐓𝐓𝟎𝟎𝟎𝟎 mode 𝝎𝝎𝟏𝟏 , the frequency 𝝎𝝎𝟐𝟐 of the 𝐇𝐇𝐇𝐇𝟏𝟏𝟏𝟏 mode with the same wave vector, and the number of downconversion channels available depending on the incident photon frequency 𝝎𝝎 (1, 3, and >3 in white blue and green
areas). Each channel has ±𝒒𝒒 and ±𝒎𝒎 degeneracies.
References[1] Álvaro Rodríguez Echarri, Joel D. Cox, and F. Javier García de Abajo, “Direct generation of entangled photon pairs in nonlinear opticalwaveguides”, Nanophotonics (2022).

Sizing single quantum dots in solvent using nano-tweezers
Hao Zhang12, Parinaz Moazzezi123, Brett Henderson23, Cristina Cordoba24, Arthur Blackburn24, Makhsud I.
Saidaminov123, Irina Paci23 and Reuven Gordon12
1. Department of Electrical and Computer Engineering, University of Victoria, 3800 Finnerty Road, Victoria, V8P 5C2, British Columbia, Canada
2. Centre for Advanced Materials & Related Technologies (CAMTEC), University of Victoria, 3800 Finnerty Road, Victoria, V8P 5C2, British
Columbia, Canada
3. Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, V8P 5C2, British Columbia, Canada
4. Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, V8P 5C2, British Columbia, Canada
E-mail: rgordon@uvic.ca

Cesium lead halide perovskite quantum dots (PQDs) promising solution-based optical materials because of theiroutstanding photonic performance [1]. With the great breakthroughs in studying PQDs, many applications have beendeveloped (e.g., single-photon emitters [2], improved solar cells [1]). Based on the quantum confinement, the emission
wavelengths from PQDs vary with size [3]. Producing and measuring the dots with uniform and controllable size has
been a goal to improve the performance in device applications. Several groups have refined the fabrication processes
to obtain good size uniformity; however, this usually involves transmission electron microscope analysis a posteriori,
which is not convenient for characterization. Sizing PQDs insolvent would be a good approach when producing PQDs
with uniform size [3], allowing for in-situ monitoring.
In this paper, we present an approach to characterize in-situ the size of individual quantum dots and correlate thiswith their optical spectrum to see the impact of quantum confinement. We observe and analyze the heterogeneity of
PQDs insolvent by using optical tweezers with DNH aperture. From the Brownian motion characteristic signal
collected by an avalanche photodiode, we calculate the standard deviation and autocorrelation time constant of eachsingle trapping event, as is shown in Fig. 1(a), which has a slope of -0.67 on a log-log plot, as expected from theory.
With the linear relationship between the standard deviation and emission spectrum, as is shown in Fig. 1(b), we cananalyze and estimate the physical size of the single dot in solution. By using a simple calculation model of the
Schrödinger equation, we calculate the bandgap as a function of particle size, which has a good agreement with ourexperiment result.

Fig. 1 (a) The standard deviation against the autocorrelation time constant of single PQD trapping collected by using DNH opticaltweezer. The curve of standard deviation against autocorrelation time constant is about the power of -0.68 with the best fit, which
has a good agreement with the theoretical calculation in our previous work [4]. (b) The standard deviation from the trapping event
has a linear relationship with the emission wavelength of the single PQD. The single PQD’s size can be estimated by a simple
calculation.

References[1] Stranks, S. D., Snaith, H. J. (2015). Metal-halide perovskites for photovoltaic and light-emitting devices. Nature nanotechnology, 10(5), 391402.
[2] Morozov, S., Vezzoli, S., Myslovska, A., Di Giacomo, A., Mortensen, N. A., Moreels, I., & Sapienza, R. (2021). Purifying single-photon
emission from a CdSe/CdS colloidal quantum dot. arXiv preprint arXiv:2111.09090.
[3] Dong, Y., Qiao, T., Kim, D., Parobek, D., Rossi, D., & Son, D. H. (2018). Precise control of quantum confinement in cesium lead halide
perovskite quantum dots via thermodynamic equilibrium. Nano letters, 18(6), 3716-3722.
[4] Wheaton, S., Gordon, R. (2015). Molecular weight characterization of single globular proteins using optical nanotweezers. Analyst, 140(14),4799-4803

Tip-Enhanced Strong Coupling (TESC):
Quantum coherent control of single emitters at room temperature
Benjamin G. Whetten1, Kyoung-Duck Park2, Molly A. May1, Matthew Pelton3, and Markus B. Raschke1,*
1. Department of Physics and JILA, University of Colorado, Boulder, CO 80303, USA
2. Department of Physics, School of Natural Sciences, Ulsan National Institute of Science and Technology, 50 UNIST-gil, Eonyang,-eup, Uljugun, Ulsan, South Korea
3. Department of Physics, UMBC (University of Maryland, Baltimore County), Baltimore, Maryland, 22150, USA
E-mail: markus.raschke@colorado.edu

Emerging quantum technologies with applications in sensing, metrology, and information processing rely on thecoherent control of quantum states which can be achieved through optical cavities with hybridization and control oflight-matter interaction. Traditionally, micro-cavities such as photonic crystals have been used to reach strong couplingof photons to single quantum emitters. However, because of the diffraction limited mode volume of micro-cavities,
cryogenic temperatures are required to overcome decoherence. In contrast, plasmonic nano-cavities confine light toorders of magnitude smaller dimensions with nanometer-scale mode volumes, opening pathways to quantum controlof solid-state emitters even at room temperature.
Here, we demonstrate and apply tip-enhanced strong coupling (TESC), to induce, image, and control single quantum
emitters in the strong coupling regime. Using a shear force atomic force microscope, we position a plasmonic nanotip with sub-nm precision above a metallic substrate to form a plasmonic pico-cavity with controllable mode volume
and position (Fig. 1a). Unlike static plasmonic nano-cavities, the scanning probe in TESC enables imaging andspectroscopy of different quantum emitters at tunable coupling strengths all within the same cavity. We demonstratestrong coupling with Rabi splitting up to 160 meV in 8 nm CdSe/ZnS quantum dots (QDs) coated in a 0.5 nm layer of
Al2O3 [1,2]. By controlling the nano-tip position, we reversibly control the coupling behavior of the cavity-emitter
system with sub-nm precision (Fig. 1b). Furthermore, by probing QDs of different resonant energies, we observe ananti-crossing in the hybridized energy levels with splitting up to 100 meV (Fig. 1c).

Fig. 1 (a) Tip enhanced strong coupling (TESC) of various quantum emitters in the pico-cavity formed between the nano-tip andmirror substrate. The cavity resonance (SPP) hybridizes with the quantum emitter energy levels to form strongly coupled polariton
states. (b) Rabi splitting of the quantum emitter photoluminescence as a function of tip-emitter distance showing sub-nm precisioncontrol. (c) Anti-crossing of the hybridized energy levels as a function of quantum dot detuning from the cavity.

To obtain pico-cavity mode volumes, we extend TESC to sub-nm height emitters such as excitons and defects in twodimensional (2D) materials. The reduced dimensionality of 2D materials allows the preparation of stable quantum
emitters in few-layer samples that enable smaller mode volumes and thus higher coupling strengths. Here, we firstinvestigate defects such as nitrogen vacancies in hexagonal boron nitride which exhibit strong photoluminescenceacross a range of wavelengths [3,4]. We further discuss the extension of pico-cavity control of competing relaxation
pathways by distance control and modeling of coupled radiative and non-radiative pathways in heterostructures oftransition metal dichalcogenides [5].
TESC thus offers unprecedented control of coherent interactions with quantum emitters in the strong coupling regime
at room temperature. The generalization of TESC to a variety of single emitters will further enable the developmentof a wide array of quantum sensing and information devices for operation in ambient conditions.
References[1] K. D. Park, et al., "Tip-enhanced strong coupling spectroscopy, imaging, and control of a single quantum emitter," Sci. Adv. 5, (2019).
[2] M. A. May, et al., "Nano‐Cavity QED with Tunable Nano‐Tip Interaction," Adv. Quantum Technol. 3, 1900087 (2020).
[3] T. T. Tran, et al., "Quantum emission from hexagonal boron nitride monolayers," Nat. Nanotechnol. 2015 111 11, 37–41 (2015).
[4] Y. Chen, et al., "Solvent-Exfoliated Hexagonal Boron Nitride Nanoflakes for Quantum Emitters," ACS Appl. Nano Mater. 4, 10449–10457(2021).
[5] M. A. May, et al., "Nanocavity Clock Spectroscopy: Resolving Competing Exciton Dynamics in WSe2/MoSe2Heterobilayers," Nano Lett. 21,
522–528 (2021).

FRET-mediated Collective Blinking of Self-Assembled Stacks of
Semiconducting Nanoplatelets
Zakarya Ouzit1, Jiawen Liu1, Juan Pintor1, Lilian Guillemeney2, Benoît Wagnon2,
Benjamin Abécassis2, Laurent Coolen1
1. Sorbonne Université, CNRS, Institut des NanoSciences de Paris, INSP, F-75005 Paris, France
2. Université de Lyon, CNRS, Ecole Normale Supérieure de Lyon, Laboratoire de Chimie UMR 5182, F-69007 Lyon, France
E-mail: zakarya.ouzit@sorbonne-universite.fr

The synthesis of quasi-2D semiconducting nanoplatelets is common and easily achievable after years of study
and development. Because of their particular shape, they present interesting optical properties: large oscillator
strength, low Stokes shift and negligible inhomogeneous line width. The behavior of single nanoplatelets has been
widely studied and different applications are investigated nowadays. Electronic devices (LEDs, field effecttransistors…) or optical sources based on semiconducting nanoplatelets can be proposed as potential applications. In
most cases, the particles are not used as individual emitters, but as ensembles in packed layers. To that extent,
understanding the effects of nanoparticles on one another and their interactions is a topical issue in order to anticipate
their collective behavior as a stack. Studies on films of close-packed semiconducting nanoplatelets showed theparticles interact through FRET (Förster Resonance Energy Transfer), a non-radiative energy transfer byelectromagnetic dipole-dipole interaction, widely studied used in biophysics and imaging.
Our latest interests were focused on linear self-assembled chains of CdSe nanoplatelets (TEM image in fig 1a)[1,2]. They play the role of a model system for the study of the platelet-platelet interactions. Indeed, the selfassembly protocol allows us to obtain a well-ordered stack with a homogeneous particle to particle spacing. Their
length varies from one chain to another, from several 100 nm to 3-4 µm. We showed that in such stacks,
nanoplatelets interact through FRET, leading to exciton diffusion along the chains with a characteristic diffusion
length of around 500 nm [3].

Fig. 1. (a) TEM image of CdSe nanoplatelets chains. (b) Fluorescence image with deconvoluted PSF of a typical single platelet
chain under wide-field mercury lamp excitation. (c) Time-position diagram of the intensity along the chain of Fig.1b showing
collective intensity fluctuations (same colorbar for both Fig. 1b and 1c). (d) Schematic representation of FRET-mediatedcollective blinking induced by a quenching nanoplatelet along a platelet chain under uniform excitation.

Here, we study the fluorescence fluctuations of self-assembled chains of CdSe nanoplatelets by imaging themthrough a micro-photoluminescence setup. We show on fig. 1b the fluorescence image of a single chain under widefield mercury lamp excitation after deconvoluting the PSF of the imaging system. We acquired movies of the chainsthat showed fluctuations of the intensity. On fig. 1c, we plotted the time-position fluorescence diagram of the chain
shown on fig 1b, showing the intensity profile along the y-axis evolving over time. One can spot “bright” states ofemission and also “dark” ones where tens of nanoplatelets are switched off at the same time. Even stacked, it appears
that the platelets blink as if they were single but collectively. We propose on fig 1d a mechanism to explain thiscollective blinking. We argue that FRET-diffusion and quenching nanoplatelets, being the site of fast non-radiative
exciton recombination, drive this collective blinking: the excitons created along the chains would be diffused by
FRET to the quenching sites and recombine non-radiatively. A 1D-random-walk model for the excitons diffusion
supports our hypothesis.
References[1] Abécassis, B., “Three-dimensional Self Assembly of Semiconducting Colloidal Nanoparticles: from fundamental forces to collective opticalproperties”, Chem Phys Chem, 17, 618-631 (2016)[2] Guillemeney, L. et al, “Curvature and Self-Assembly of Semiconducting Nanoplatelets”, Comm Chem 5, 7 (2022)[3] Liu, J. et al, “Long Range Energy Transfer in Self-Assembled Stacks of Semiconducting Nanoplatelets”, Nano Lett, 20, 3465–3470 (2020)

A scalable route to single-photon sources at low-loss wavelengths by anchoring
nanocrystals with a single Er3+ dopant
Adriaan L. Frencken1, Michael Dobinson2, Reuven Gordon2, Frank C. J. M. van Veggel1
1. Department of Chemistry, University of Victoria, Victoria, British Colombia V8W 2Y2, Canada
Centre for Advanced Materials & Related Technologies (CAMTEC), University of Victoria, Victoria, British Columbia V8W 2Y2,
Canada2. Department Electrical and Computer Engineering, University of Victoria, Victoria, British Columbia V8W 2Y2, Canada
Centre for Advanced Materials & Related Technologies (CAMTEC), University of Victoria, Victoria, British Columbia V8W 2Y2,
CanadaE-mail: adriaanfrencken@uvic.ca

Quantum information science is a rapid growing scientific field, involving computation using quantum states withthe goal to outcompete classical computation. A promising candidate for this is the photonic qubit and scalable
fabrication of a single photon source is highly sought after.[1][2] Previously, our groups have demonstrated theisolation of single photon sources using optical traps to isolate nanoparticles (NPs) doped with a single Er3+
ion.[3][4] We are currently developing methods to anchor these NPs permanently in order to develop a scalable routefor the fabrication of single photon sources.
Here we present an anchoring method based on the photo-removal of thiol protecting groups on the NP surface,allowing formation of a bond between the sulfur and the gold surface of the trapping aperture. Oleate-capped
NaYF4(:Er3+) NPs of ca. 20 nm were coated with thiol functionalised phospholipids that were subsequently treatedwith the photo-removable protecting group (PG) 2-bromo-4’-hydroxyacetophenone. Succesful protection and phototriggered deprotection were demonstated using thiol detecting agents.
For the anchoring demonstration, a 980 nm laser was used to trap the nanoparticles in a double nanohole (DNH)
aperture optical tweezer in a 70 nm thick gold film with a 7 nm Ti adhesion layer. After verification of successful
trapping, light from a 340 nm LED was used to trigger the release of the PGs and allow reaction of the sulfur groups
with the gold surface. This process is demonstrated schematically in Fig. 1 (left). EM was used to show the presenceof NPs after removal of the sample from the trapping optical beam, Fig. 1 (right).

Fig. 1. (Left) Schematic representation of light triggered anchoring of NaYF4 NPs doped with a sinle Er3+ ion. (Right) SEM image of a single NP
anchored on the wall of a DNH gold aperture.

With our upcoming experiments, we aim to demonstrate emission from anchored NPs doped with a single Er3+ ion in
the absence of the trapping beam. The single photon nature of the emission from the anachored NPs can then beverified, and the method can be used to up-scale the isolation of single Er3+ doped NPs for mass fabrication of single
photon sources for photonic qubits.
References[1] Dibos, A. M., et al. (2018). "Atomic Source of Single Photons in the Telecom Band." Phys. Rev. Lett., 120(24), 243601.
[2] Eisaman, M. D. et al. (2011). “Invited Review Article: Single-Photon Sources and Detectors.” Review of Scientific Instruments, 82(7),071101.
[3] Alizadehkhaledi, A., et al. (2020). "Isolating Nanocrystals with an Individual Erbium Emitter: A Route to a Stable Single-Photon Source at1550 nm Wavelength." Nano Letters 20(2): 1018-1022.
[4] Sharifi, Z.., et al. (2021). "Isolating and Enhancing Single-Photon Emitters for 1550 Nm Quantum Light Sources Using Double Nanohole
Optical Tweezers.” J. Chem. Phys., 154(18), 184204.

Strong coupling dynamics and multi-photon correlations
in waveguide QED using three coupled qubits
Sofia Arranz Regidor and Stephen Hughes
Queen’s University, 99 University Avenue, Kingston, ON, K7L 3N6, Canada
E-mail: 18sar4@queensu.ca

The interaction between light and atoms and resonant materials has been a critical field of study in quantum
mechanics for decades, leading to new quantum protocols and technologies. Photons coupled to atoms and resonant
few-state systems present a fundamental model system in quantum optics, and when implemented on photonic chips,
quantum circuits enabled through waveguide quantum electrodynamics (QED) are becoming an important field of
research in nanophotonics and quantum optics. In waveguide QED, the interaction between quantum emitters (e.g.,quantum dots or qubits) in the presence of a radiation channel is quasi one-dimensional, where the qubits are coupled
to a continuum of quantized field modes. These hybrid systems show several new phenomena that are unique to the
waveguide geometry. For example, in the presence of a time-delayed coherent feedback, qubits in a waveguide gives
rise to interesting effects such as long-lived vacuum Rabi oscillations and multi-photon-matter entangled states [1].
Partly motivated by recent experimental work that realized qubit strong coupling behavior with atom-like mirrors[2], we explore three coupled qubits in a waveguide environment [Fig 1(a)]. We fully account for multi-photon effects
and non-Markovian dynamics of the qubits, by implementing a Matrix Product State (MPS) approach [3], a powerfulquantum model to represent the product state of many photons and qubits. In Fig. 1(b), we show example qubit
dynamics, for a target qubit (center qubit, initially excited) as well as the mirror qubits, including the effects of chiralityand delay time between the mirrors. We show how cavity-like phenomena (mediated by the mirror qubits), such as
vacuum Rabi oscillations, can have their performance significantly improved through non-Markovian feedback.

Fig. 1 (a) Schematic of three qubits (quantum dots or two-level systems) in a waveguide-QED system. The probe qubit is in thecenter. (b) Probe and mirror population dynamics for three different delay times, scaled by the nominal radiative decay rate forthe target qubit into the waveguide (L means left scattering and R means right scattering rate). The top figures show symmetriccoupling while the bottom ones explore chiral qubit behavior (where the dashed grey line compares to the symmetric results).

To more fully explore the quantum statistics of light, we also calculate the multi-photon quantum correlation
functions for the three-qubit waveguide system, as well as the emitted spectrum, which show interesting phenomena
when multi-photon resonances come into play. In the presence of a nonlinear pump field, we will demonstrate how
well this quantum nonlinear system mimics a cavity-QED system and when it offers a significant departure, with somemajor advantages for exploring and controlling non-classical states of few photons and matter.
References[1] Arranz Regidor, S., and Hughes, S. 2021, “Cavitylike strong coupling in macroscopic waveguide QED using three coupled qubits in the deep
non-Markovian regime”, Phys. Rev. A 104, L031701.
[2] Mirhosseini, M., Kim, E., Zhang, X., Sipahigil, A., Dieterle, P. B., Keller, A. J., Asenjo-Garcia, A., Chang, D. E., and Painter, O. 2019,“Cavity quantum electrodynamics with atom-like mirrors”, Nature 569, 692-697.
[3] Arranz Regidor, S., Crowder, G, Carmichael, H.J, and Hughes, S. 2021, “Modeling quantum light-matter interaction in waveguide QED withretardation, nonlinear interactions, and a time-delayed feedback: Matrix product states versus a space-discretized waveguide model”, Phys. Rev.
Research, 3 023030.

Quantum Many-Body Study of Hybrid Plasmon–Exciton Systems at the
Subnanometer Scale: Influence of Electronic Orbital Coupling
Antton Babaze1,2, Ruben Esteban1,2, Andrei G. Borisov3, and Javier Aizpurua1,2
1. Materials Physics Center CSIC-UPV/EHU, Paseo Manuel de Lardizabal 5 20018 Donostia-San Sebastián, Spain
2. Donostia International Physics Center DIPC, Paseo Manuel de Lardizabal 4 20018 Donostia-San Sebastián, Spain
3. Institut des Sciences Moléculaires d’Orsay, UMR 8214 CNRS-Université Paris-Saclay Bât. 520, 91405 Orsay Cedex, France
E-mail: anttonbabaze@dipc.org

Due to the excitation of plasmonic resonances, metallic nanoparticles (MNPs) strongly enhance the amplitude of
the incident electromagnetic field at optical frequencies and thus can excite very efficiently electronic transitions inquantum emitters (QEs) located nearby. Coupled QE–MNPs systems have been extensively exploited in many
spectroscopy and microscopy techniques and, parallel to the experimental progress, substantial theoretical effort has
been devoted to describe the optical response of such systems. Typical simulations based e.g. on classical or
quantum electrodynamics only account for the electromagnetic coupling between QEs and MNPs, and are often able
to successfully reproduce experimental results in situations of relatively large QE–MNPs separation [1]. However, at
subnanometric distances, quantum phenomena associated with the electronic coupling between the orbitals of the QE
and the MNP can play a crucial role. In such a situation, a quantum many-body treatment of the problem is essential
to describe the optical response of the system. In this context, recent works based on time-dependent density
functional theory (TDDFT) have shown that a QE bridging two MNPs can trigger charge-transfer processes due tothe electronic coupling between the QE and MNPs at subnanometric distances [2,3].
In this work, we use TDDFT simulations to study the influence of electronic coupling on the optical interaction
between QEs and MNPs [4]. The studied system consists of a QE supporting a single HOMO–LUMO transition
placed within the nanogap formed by two spherical MNPs (Figure 1a). The gap separation and the QE transitionenergy are varied to study different regimes of QE−MNPs electronic coupling and identify the onset of quantum
effects that strongly affect the optical response of the system. The TDDFT calculations reveal that the hybridization
between the electronic states localized at the QE and at the MNPs produces a drastic quenching of the LUMO at(sub)nanometric gap separations that hinders the excitation of the HOMO–LUMO transition in the QE. As aconsequence, the coupling strength between the QE and light is dramatically reduced, and thus, the optical response
obtained within TDDFT significantly deviates from the classical electromagnetic prediction (Figure 1b). Further, ourwork demonstrates that electronic coupling can frustrate strong coupling between QEs and MNPs in situations where
the system would be classically in the strong-coupling regime. This work thus shows the importance of electronic
coupling between the orbitals localized at the QE and at the MNPs for subnanometric separations and stress the needto go beyond the electromagnetic interaction picture usually adopted to describe these systems.

Fig. 1: (a) Sketch of the system under study. A quantum emitter (QE) is placed at the nanogap formed by two spherical metallic
nanoparticles (MNPs). The HOMO and LUMO of the isolated QE electronically hybridize with the electronic states of the
MNPs. (b) Absorption cross-section spectra of the coupled QE–MNPs system calculated within two different frameworks. Left:a classical electromagnetic model only accounting for the electromagnetic (EM) coupling. Right: TDDFT accounting for boththe EM and the electronic coupling.

References[1] Zhang, Y. et al. 2017. Nat. Commun. 8, 15225.
[2] Song, P. et al. 2011. J. Chem. Phys.134, 74701.
[3] Kularni, V. et al. 2015. ACS Photonics, 2, 987.
[4] Babaze, A. et al. 2021. Nano Lett., 21, 8466.

Electrically-pumped QD emission from single plasmonic nanoantennas
Junyang Huang, Shu Hu, Dean Kos, Jeremy J Baumberg
NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, United Kingdom
E-mail: jh2002@cam.ac.uk

Spontaneous emission from semiconductor quantum dots (QDs) at room temperature is attractive for nanophotonic
applications due to wavelength-tunable emission, high radiative quantum efficiency, and ease of integration with
devices. Here we integrate single/few QDs into plasmonic nanocavities for electrically pumped emission, showing
strong coupling is reliably obtained.
Plasmonic nanoantennas support highly localized field enhancement (I/I0 ≈ 106) [1], a Purcell-enhanced photonic
density of states (FP= γsp/γsp0 ≈ 103), and broadband resonances (Q factor ≈ 10-30), making them desirable resonators
for tailoring QD emission at room temperature [2,3]. The substantial Purcell enhancement in self-assembled plasmonic
cavities boosts the fluorescence intensity and accelerates the intrinsically slow emission of the QDs (τQD ≈ 1-20 ns),matching ultrafast optoelectronic devices needing emission rates >100 GHz. Moreover, the optical modes defined by
the nanoantenna geometry impose directionality to QD emission, offering the opportunity to optimize the coupling
efficiency into photonic devices. Despite increasing interest in the integration of colloidal QDs into plasmon-enhanced
antennas, electrically-driven emission from such metal junctions has yet to be demonstrated.
Here, we demonstrate a self-aligned and robust electrically-contacted plasmonic junction for QD optoelectronics(Fig.1a), where a near-perfect monolayer of CdSe QDs is sandwiched between a flat Au surface electrode and a single
gold nanoparticle (AuNP) [5]. Embedding this nanoparticle-on-mirror (NPoM) geometry in a cross-bar junction device[4] facilitates electrical excitation of QD excitons and their Purcell-enhanced photoemission, typically quenched close
to metal surfaces. Driving emission at a bias of 2 V allows us to follow fluctuations of the intensity and the spectral
shape of the QD electroluminescence (Fig.1b). Tuning the optimal coupling to the band-edge exciton in these
extremely compact cavities with ultrasmall mode volumes ~50nm3, we observe Rabi splitting in theelectroluminescence spectrum (Fig.1c). Now controlling the number of QDs within the cavity makes a variety of roomtemperature quantum-optical effects open to experimental investigation in a reliable route.

Fig. 1 a, Electrically-pumped photoemission from monolayer of CdSe QDs sandwiched between a single Au nanoparticle and a Au
bottom electrode. b, Evolution of electrical current (blue) and electroluminescence intensity (red) from a single plasmonic junction
as a result of bias applied (grey). c, Spectra of nanoantenna-dressed QD electroluminescence in weak (blue) and strong (red)coupling regimes.

References
[1]

[2]
[3]
[4]
[5]

Huang, J.; Grys, D.-B.; Griffiths, J.; de Nijs, B.; Kamp, M.; Lin, Q.; Baumberg, J. J. Tracking Interfacial Single-Molecule
PH and Binding Dynamics via Vibrational Spectroscopy. Science Advances 2021 7, eabg1790.
Hoang, T. B.; Akselrod, G. M.; Argyropoulos, C.; Huang, J.; Smith, D. R.; Mikkelsen, M. H. Ultrafast SpontaneousEmission Source Using Plasmonic Nanoantennas. Nat Commun 2015, 6 (1), 7788.
Huang, J.; Ojambati, O. S.; Chikkaraddy, R.; Sokołowski, K.; Wan, Q.; Durkan, C.; Scherman, O. A.; Baumberg, J. J.
Plasmon-Induced Trap State Emission from Single Quantum Dots. Phys. Rev. Lett. 2021, 126 (4), 047402.
Kos, D.; Assumpcao, D. R.; Guo, C.; Baumberg, J. J. Quantum Tunneling Induced Optical Rectification and PlasmonEnhanced Photocurrent in Nanocavity Molecular Junctions. ACS Nano 2021, 15 (9), 14535–14543.
Huang, J.; Hu, S; Kos, D; Baumberg, JJ; submitted (2022)

Addressing the correlations of photons emitted from an ultrastrongly coupledsystemÁlvaro Nodar1, Ruben Esteban1, Unai Muniain2, Javier Aizpurua1,2, Mikołaj Kajetan Schmidt1,2,3

1. Centro de Física de Materiales CFM (CSIC-UPV/EHU), Paseo Manuel de Lardizabal, 5, 20018, Donostia, Spain
2. Donostia International Physics Center DIPC, Paseo Manuel de Lardizabal, 4, 20018, Donostia, Spain
3. Macquarie University Research Centre for Quantum Engineering (MQCEQ), MQ Photonics Research Centre, School of Mathematical andPhysical Sciences, Macquarie University, NSW 2109, Sydney, Australia
E-mail: alvaro_nodar001@ehu.eus

Intensity correlations describe the statistical properties of photons emitted by a coupled system and help todetermine its dynamics and whether the nature of the emitted light is classical or quantum. In this work, we study theintensity correlations of an incoherently-driven two-level system (TLS), such as an electronic transition of a quantum
well, interacting with an electromagnetic cavity. We focus on the ultrastrong coupling regime, where the couplingstrength g0 is comparable to the natural energies of the system. In this regime, the system strongly deviates from thesimplified, Jaynes-Cummings model (see Fig. 1), leading to the emergence of novel features in the emission spectraand statistics [1,2].
We use two different descriptions to model the cavity-TLS interaction, based on cavity quantum electrodynamics(cavity-QED): (i) the Jaynes-Cummings model and (ii) the gauge-fixed (GF) Rabi model [3-5]. The Jaynes-Cummings
model is widely used to describe the dynamics of coupled systems and correctly describes the interaction in many
practical configurations of cavity-enhanced light emission but fails in the ultrastrong coupling regime. Fig. 1 shows
the intensity correlations (g(2)) obtained within this model (red line) for different coupling strengths ranging from theweak coupling to the ultrastrong coupling regime. The intensity correlations exhibit anti-bunching (g(2)<1), indicating
non-classical emission. On the other hand, the recently developed GF Rabi model accurately describes the TLS-cavity
interaction also in the ultrastrong coupling regime [3-5]. The resulting intensity correlations (blue line in Fig. 1) arevery similar to those obtained with the Jaynes-Cummings model for weak and moderate coupling strengths. However,the GF Rabi model indicates that the photons become highly bunched in the ultrastrong coupling regime (g(2)>1),
deviating from the Jaynes-Cummings results. To analyze this difference, we calculate the correlations obtained after
filtering the emitted light to select pairs of photons of particular frequencies (two-color correlation maps). Thisapproach allows for gaining additional information about the processes involved in the light emission [6].
Understanding the changes in the statistical nature of the light emitted in cavity-coupled systems provides important
information to fully characterize light emission from quantum devices in the strong and ultrastrong coupling regimes.

Fig. 1 Intensity correlations (g(2)) of a cavity coupled to a two-level system (TLS) as a function of the normalized coupling strength(g0 /⍵0, with ⍵0=1 eV the natural frequency of the TLS and of the cavity). The red and blue lines correspond to the JaynesCummings and the gauge-fixed (GF) Rabi calculations, respectively. The dashed line corresponds to g(2)= 1 and separates theregions where bunching (g(2)>1) and antibunching (g(2)<1) are found. For these calculations, the TLS is pumped incoherently witha rate Pσ=1 meV, and the losses of the cavity and of the TLS are �=50 meV and Ɣ=0.1 meV, respectively.

References[1] Forn-Díaz P., et. al., 2017 Nat. Phys. 13, 39[2] Kockum A. F., et al., 2019, Nat. Rev. Phys. 1, 19[3] Salmon W., et al., 2021, arXiv:2102.12055[4] Settineri A., et al., 2021, Phys. Rev. Research 3, 023079[5] Di Stefano O., et al., 2019 Nat. Phys. 15, 803[6] Schmidt M. K., et al. 2021 Quantum Sci. Technol. 6, 034005

First-principles study of plasmon-molecule coupling andcharge transfer in Ag nanoparticle dimers
Bruno Candelas1, Nerea Zabala2, Daniel Sánchez-Portal1, Javier Aizpurua1

1. CFM-MPC, Centro mixto CSIC-UPV/EHU, and DIPC, Manuel de Lardizabal 5, 20018, Donostia, Spain
2. Department of Electricity and Electronics, FCT-ZTF, UPV/EHU, Bº Sarriena s/n, 48940 Leioa, Spainbcandelas001@ikasle.ehu.eus

When an organic molecule is placed inside a plasmonic cavity formed by two metallic nanoparticles (MNPs)
under illumination, the electronic transitions of the molecule couple to the electromagnetic modes of the cavity, so
that, in the strong-coupling regime, two hybrid light--matter modes called polaritons emerge [1]. Atomistic ab-initio
methods accurately describe the coupling between MNPs and molecules at this nanometer scale [2]. In this work, we
study the optical absorption spectra of porphyrin molecules coupled to silver nanoparticle dimers from firstprinciples, by using the ab-initio SIESTA software to obtain the ground state of the system in the Kohn-Shamscheme with a basis set of numerical atomic orbitals [3], and the TDDFT code PyNAO [4, 5], which uses its own
iterative scheme to obtain the linear response using a linear combination of atomic orbitals as basis set, to computethe optical excitations. The results show the splitting of the plasmonic resonance in two distinct polaritons, acharacteristic feature of the strong light-matter coupling regime. We analyse the dependence of the coupling strength
on the geometrical features of the system, such as the separation between the MNPs or their relative orientation. For
certain gap morphologies, our simulations reveal the existence of a Charge Transfer Plasmon at lower frequencies, astate which is predicted to emerge when the molecular energy level is resonant with the Fermi level of the MNPs [6].
Moreover, we show that the strength of the charge transfer modes can be tuned by artificially shifting the molecularenergy levels relative to those of the MNPs.
F
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he system under study, composed of two icosahedral Ag309 nanoparticles with a 2,3-Dihydroporphyrin molecule placed in the
gap between them. The system is displayed in the tip-to-tip configuration, with a gap size D=1.5 nm. The system is excited bylight polarized along the dimer axis direction. b) Absorption spectra of the complete system for gap size values in the range
between D=1.4 nm (bottom) and D=1.8 nm (top). The new emerging Lower and Upper Polaritons are marked by yellow andgreen dots, respectively. c) Isosurfaces of induced density at the emerging resonances for D=1.4 nm. d) Low energy part of theabsorption spectrum for the bare dimer (green), the isolated porphyrin molecule (dotted black), and the complete system in boththe tip to tip (blue) and facet to facet (red) configurations, with D=1.4 nm.

References[1] García-Vidal, F. J.; Ciuti, C.; Ebbesen, T. W. 2021 . Science, 373, eabd0336.
[2] Rossi, T. P.; Shegai, T.; Erhart, P.; Antosiewicz, T. 2019. Nat. Commun., 10, 3336.
[3] Soler, J. M.; Artacho, E.; Gale, J. D.; García, A.; Junquera, J.; Ordejón, P.; Sánchez-Portal, D. 2002. J.Phys.: Condens. Matter, 14, 2745.
[4] Koval, P.; Barbry, M.; Sánchez-Portal, D. 2019. Comput. Phys. Commun. , 236, 188.
[5] Barbry, M.; Koval, P.; Marchesin, F.; Esteban, R.; Borisov, A. G.; Aizpurua, J.; Sánchez-Portal, D. 2015. Nano Lett.., 15, 5, 3410-3419.

Quantum Surface Effects in a Plasmonic Nanoantenna–Emitter System:
Time-Dependent Density Functional Theory vs. Semiclassical Approach
Antton Babaze1,2, Eduardo Ogando3, P. Elli Stamatopoulou4, Christos Tserkezis4, N. Asger Mortensen4,5,
Javier Aizpurua1,2, Andrei G. Borisov6, and Ruben Esteban1,2
1. Materials Physics Center CSIC-UPV/EHU, Paseo Manuel de Lardizabal 5 20018 Donostia-San Sebastián, Spain
2. Donostia International Physics Center DIPC, Paseo Manuel de Lardizabal 4 20018 Donostia-San Sebastián, Spain
3. Department of Physics, University of the Basque Country UPV/EHU, Paseo de la Universidad 7 01006 Vitoria-Gasteiz, Spain
4. Center for Nano Optics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
5. Danish Institute for Advanced Study, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
6. Institut des Sciences Moléculaires d’Orsay, UMR 8214 CNRS-Université Paris-Saclay Bât. 520, 91405 Orsay Cedex, France
E-mail: anttonbabaze@dipc.org

The electromagnetic coupling between quantum emitters (QEs) and plasmonic metallic nanoparticles (MNPs) has
attracted great interest in the field of nanophotonics due to the ability of MNPs to strongly enhance the absorption
and emission rate of QEs located in close proximity. Typically, the electromagnetic QE–MNPs interaction isaddressed using the classical local-response approximation (LRA) of metals, which has successfully described many
physical phenomena of interest when the size of the MNPs and the QE–MNPs distance are relatively large. However,quantum phenomena such as electron spill in/out at the metallic interface, surface-enabled Landau damping, or
nonlocal dynamical screening can significantly influence the electromagnetic interaction in practical QE–MNPsconfigurations involving small QE–MNPs separation distances [1]. In this context, time-dependent density functional
theory (TDDFT) is well suited to naturally account for all quantum phenomena occurring in the QE–MNPs
interaction [2]. Moreover, computationally less-demanding semiclassical approaches such as the Feibelman model
have been also used to capture some of these quantum effects [3]. The Feibelman formalism incorporates ab initio
quantum surface-response corrections at metallic interfaces in the solution of classical Maxwell’s equations bymeans of the d⊥(ω) parameter, which accounts for the position of the centroid of the induced charges at frequency ωwith respect to the classical metallic boundary [4].
This work explores the influence of quantum-mechanical effects in the electromagnetic interaction between QEs
and MNPs using TDDFT calculations within the jellium model. We first use TDDFT to study the Green’s functionthat describes the electric field experienced by a QE due to its self-interaction in the presence of a spherical MNP(Figure 1a), and then compare the results with those obtained within the Feibelman model. The QE is described as apoint dipole of amplitude pd. The analysis of the TDDFT and Feibelman results confirms that the spill out of theinduced charges and surface-enabled Landau damping produces a redshift and broadening of plasmonic resonances,not present within the LRA results (Figure 1b). Furthermore, the good agreement between the TDDFT and
Feibelman results for most QE–MNPs separations validates the use of the Feibelman approach in many nanoscale
systems. However, we identify situations of very small QE–MNP distance where the current implementation of the
Feibelman model is not accurate. Our study thus provides a fundamental description of quantum effects influencing
the electromagnetic interaction between QEs and MNPs and establishes the validity range of the semiclassicalFeibelman formalism.

Fig. 1: (a) Sketch of the system under study consisting of a quantum emitter (QE), modeled as a point dipole of amplitude pd, located in
front of a spherical metallic nanoparticle (MNP). The MNP is described within the quantum TDDFT by calculating the time evolution of
the electron density n0(r) (left), and within the semiclassical Feibelman formalism by incorporating quantum surface-response
corrections with the use of the d⊥(ω) parameter (right). (b) Contribution of the first seven plasmonic modes to the imaginary part of theself-interaction Green’s function obtained within the three models employed in this work. Solid lines: TDDFT. Dashed lines: Feibelman
formalism. Dashed-dotted lines: Local-response approximation (LRA).

References[1] Gonçalves, P. et al. 2020. Nat. Commun., 11, 366.
[2] Babaze, A. et al. 2021. Nano Lett., 21, 8466.
[3] Mortensen, N. A. 2021. Nanophotonics, 10, 2563.
[4] Feibelman, P. J. 1982. Prog. Surf. Sci. 12, 287.
[5] Babaze, A. et al. 2022. In preparation.

Interference-based Wide-range Dynamic Tuning of the Plasmonic Colorof Single Gold Nanoparticles
Bokusui Nakayama1, Hiroki Endo1, Yuki Hiruta1 and Toshiharu Saiki1
1. Graduate School of Keio University / 3-14-1 Hiyoshi, Kohoku-ku, Yokohama-shi, Kanagawa 223-8522 Japan
E-mail: bokusui.nakayama@saiki.elec.keio.ac.jp

Coloration in natural and artificial materials is rich in variety. Surface plasmon resonance and interference can
explain these colorations and lead to ink-free color production. In particular, plasmonic coloring using metal
nanoparticles has advantages of high resolution, low energy consumption, high brightness, and large viewing angle,
as well as color tunability through variation of the material, size, shape, and environment. Researchers have devoted
great effort to developing a high-resolution dynamic display that operates via fast tuning of plasmonic and interference
effects. They have used electrical, chemical, mechanical, and thermal modulation of the environment because of the
difficulties of tuning the material itself in real-time. Among these methods, each of which has advantages anddisadvantages in terms of speed, tunable range, and power consumption, mechanical tuning using stimuli-responsive
polymers is promising because of its potential to satisfy the requirements of a specific application.
Such stimuli-responsive polymers have also exhibited advantages in the dynamic modulation of color. Ding et al.
demonstrated modification of the surface plasmon gap mode between an Au nanoparticle (AuNP) and an Au-coatedsubstrate by utilizing the volume change of a hydrogel with temperature [1]. At low temperatures, where the hydrogel
was swelled, the gap between an AuNP embedded in the hydrogel and the substrate was large and the AuNP appeared
green under dark-field microscopic observation. When the temperature was increased, the gap was substantiallyreduced to the sub-10 nm range to induce a color change of the AuNP from green to orange. Although this approachenables reversible, repeatable, and high-speed modulation at a single-particle level by using focused laser heating, thecoverage of the color space is narrow and far from that required for color displays.
In the present paper [2], we demonstrate dynamic nanoscale coloration using single AuNPs by hybridizing
plasmon-based and interference-mode approaches. Under back-scattering white-light observation of single AuNPs,
interference between the scattered light from the AuNPs and the reflected light from the substrate gives rise to various
colorations depending on the distance between the AuNPs and the substrate (Figure 1). We experimentally examinedthe coverage of the color-space diagram and compared the color range with theoretical calculations. We also attempted
to dynamically control the color of the AuNPs by precisely tuning their distance from the substrate via the volume
change of a temperature-responsive hydrogel (Figure 2).

Fig. 1 Schematic model of our system and a set of color images of
AuNPs. Scattered light Es from an AuNP interferes with reflected
light Er from the substrate/solution interface.

References[1] T. Ding, et. al., Adv. Opt. Mater. 4(6), 877-822 (2016).
[2] B. Nakayama, et. al., Opt. Express. 29(10), 15001-15012 (2020).

Fig. 2 Time-sequence snapshots and color plots visualizingin color of an identical AuNP by heating and coolingprocesses, respectively, to induce the volume change of thehydrogel.

Furthering nano-optic techniques through the simultaneous integration ofheterodyned-tapping-mode AFM
Kevin W.C. Kwock1, Thomas Darlington2, Emanuil S. Yanev2, Natalie Fardian-Melamed2, Benedikt
Ursprung2, James C. Hone2, P. James Schuck2
1. Department of Electrical Engineering, Columbia University
2. Department of Mechanical Engineering, Columbia University
E-mail: kwk2118@columbia.edu, pjs2191@columbia.edu

Scanning tip-enhanced spectroscopy techniques such as tip-enhanced Raman scattering (TERS) and tip-enhanced
photoluminescence (TEPL) are powerful tools for investigation of opto-electronic properties of materials surfaces.
However, the improved resolution comes at the significant expense optical signal, requiring the use of higher excitation
powers which can be detrimental to samples and nano-optical probes.1-2 This leads to the current paradigm of ‘hit-ormiss’ in tip-enhanced measurements where success is heavily dependent on of fabrication of extraordinary nano-opticalprobes that can simultaneously tolerate high excitation densities and greatly enhance the signal of interest for ameasurement’s duration. Methods to increase signal/noise throughput in a system without high photon fluences on thesample/tip are thus greatly needed for imaging typically weak optical interactions, such as many Raman scattering
signals as well as nonlinear optical interactions such nano-second harmonic generation.
In this study, we present on our current efforts to improve our nano-optical studies through the incorporation oflock-in detection of tip-enhanced signals using the oscillation of an AFM-cantilever mounted nano-optical probe,
through interaction of fast single photon sensitive avalanche photo diodes and time-correlated single photon counting
electronics, a system first demonstrated by Gerton et al.3 We show that this technique can successfully image the nanoPL nanobubble in monolayer WSe2 on Au, achieving resolutions below 20 nm. Our results show the viability for lockin detection in tip-enhanced spectroscopic and show a potentially path for true on-demand nano-optical measurements.
References[1] Neacsu, C.C., van Aken, B.B., Fiebig, and Raschke, M.B. 2005. Phys. Rev. B 79, 100107.
[2] Yao, K., Zhang, S., Yanev, E., McCreary, K., Chuang, H., Rosenberger, M.R., Darlington, T., Krayev, A., Jonker, B.T., Hone, J.C., Basov,
D.N., and Schuck, P.J. 2022. arXiv:2111.06955.
[3] Gerton, J.M., Wade, L.A., Lessard, G.A., Ma, Z., and Quake, S.R. 2004. Phys. Rev. Lett. 93, 180801.
[4] Darlington, T.P. et. al. 2020. Imaging strain-localized excitons in nanoscale bubbles of monolayer WSe2 at room temperature, Nature
Nanotechnology, 15(10), 854-860.

ULF TERS imaging –a novel technique for assessing the layer interaction invertical heterostructures of 2D semiconductors.
Alvaro Rodriguez1, Andrey Krayev2, Matěj Velický1, Peng Chen3, Xiangfeng Duan4, Patrick El-Khoury5,
Otakar Frank1
1. J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 2155/3, 182 23 Prague, Czech Republic
2. HORIBA Scientific, 359 Bel Marin Keys Blvd, Suite 18, Novato CA, 94949, USA
3. School of Microelectronics, Southern University of Science and Technology; 1088 Xueyuan Avenue, Shenzhen 518055, China
4. Department of Chemistry and Biochemistry and California NanoSystems Institute, University of California, Los Angeles, USA
5. Physical Sciences Division Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA, 99352, USA
E-mail: andrey.krayev@horiba.com

Tip enhanced Raman scattering (TERS) and tip enhanced photoluminescence (TEPL) are effective tools for theassessment of nanoscale heterogeneity in mono- and a few- layer 2D semiconductors and their heterostructures. Dueto their non-destructive nature, TERS and TEPL imaging can be cross-correlated with other images conveniently
recorded using scanning probe microscopy (SPM), such as topography, surface potential, photocurrent etc, whichfurther improves our understanding of 2D semiconductors. Recent interest of the community in vertical
heterostructures of graphene and transition metal dichalcogenides (TMDs) with precise control of the twist angle
between the layers motivated us to apply and extend TERS imaging to the characterization of the WS2-WSe2 vertical
heterostructures.
WS2-WSe2 heterobilayer samples were exfoliated to PDMS and then transferred to a gold-coated silicon wafer andwere confirmed to feature large areas (tens of microns across) showing the presence of a lattice-like Moire pattern with
6-8 nm pitch. Additionally, as it almost inevitably occurs with the stacked layers exfoliated in air, large number of
nanobubbles were present in the samples. TERS imaging of larger bubbles with 785 nm excitation revealed extreme
heterogeneity of the TERS response across the bubble- at the outer edges we observed strong bands coming from WSe2
and additionally- a predominant ultralow frequency (ULF) TERS peak at around 23 cm-1 that arises from the interlayer
phonon mode was observed. To the best of our knowledge this is the first time demonstration of ULF TERS that track
low frequency inter-layer phonons, and therefore, directly report on local structure with nanometer spatial resolution.
Interestingly, this peak disappeared towards the center of the bubble, while an A’/A1g peak of WS2 simultaneously
appeared at ~416 cm-1. Careful correlation analysis of the recorded spectral nano-images showed that this WS2–likepeak was correlated to a local exciton. The same analysis paints a unique picture about the two layers in the bubble
region, which seems to be comprised of WS2-WSe2 bilayers that are separated at the apex of the nanobubble. It’s arather remarkable observation taking into account that the lateral spatial extent of this decoupling took place on the
10’s of nm length scale.
Again, somewhat surprisingly, TERS response of the areas in between the larger bubbles looked patchy showing
great similarity to the response from larger bubbles which indicates that the sample had a developed network of smaller
and larger nanobubbles that inevitably affected the electronic band structure of WS2-WSe2 vertical heterostructures,
which brings us to the conclusion that any far field Raman spectra obtained on exfoliated vertical heterostructures
should be taken with certain caution unless a solid proof of the lack of nanobubbles in the investigated sample isprovided.
Finally, we should note that despite the demonstrated utility for characterization of the layer interaction in vertical
heterostructures, ULF TERS of 2D semiconductors requires significant work for proper understanding of the resonant
effects and the resulting band assignments. Unlike the case of conventional ULF Raman response in TMDs, ULF
TERS response changes quite dramatically as the excitation laser wavelength changes, both the intensity and thespectral position-wise. Examples of this apparently resonant behavior will also be presented.

TERS Characterization of Functionalized Gold Nanostructures
for Improved Biosensors.
JF Bryche1, M. Vega1,2, A. Tempez3, T. Brulé3, T. Carlier3, J. Moreau1,2,
P.G. Charette1, M. Chaigneau3, M. Canva1,2
1. Laboratoire Nanotechnologies Nanosystèmes (LN2 – IRL 3463) – CNRS/ Institut Interdisciplinaire d’Innovation Technologique(3IT) /Université de Sherbrooke, Sherbrooke, Canada.
2. Laboratoire Charles Fabry (LCF), Université Paris-Saclay, Institut d'Optique Graduate School, CNRS, Palaiseau, France.
3. Horiba FRANCE SAS, Palaiseau, France
E-mail: jean-francois.bryche@usherbrooke.ca

Plasmonic gold nanostructures are being used to develop high-performance biosensors. The confinement ofelectromagnetic fields far beyond the diffraction limit has led in recent design to single-molecule detection throughsurface-enhanced Raman spectroscopy (SERS) [1]. Tip-Enhanced Raman Spectroscopy (TERS) characterization,
which has emerged as a powerful analytical technique providing high chemical sensitivity for surface molecularmapping with nanoscale spatial resolution, can provide nano-spatially resolved response and help in designing highly
sensitive and high-resolution biosensing structures.
This work examined the TERS performance of functionalized gold nanodisk arrays on a gold-coated glass
substrate. These samples have shown results in SERS [2] upon coupled plasmonic modes: the gold layer sustains
propagative surface plasmons while the nanostructures sustain localized surface plasmon resonances. Coupling
between them can occur in specific conditions and give rise to hybrid modes [3]. Nano-resolved TERS response
distribution from grafted thiophenol molecules on nanodisks of 110 and 220 nm diameter feature strong signal
localization on the periphery of the nanostructures, in agreement with numerical modeling [4]. This highlights theimportance of grafting molecules on high electric field locations to optimize detection sensitivity and speed at low
molecular concentrations.

a)

b)

c)

Fig. 1 a) SEM picture of gold nanodisk arrays on gold film with 220nm diameters and 400nm periods. b) TERS mapping of 220
nm gold nanodisks with a 638 nm laser. In the TERS image, the pixel size is 10×10 nm². c) Raman signal for three identified
regions of the sample: Top – Edge – Between. Each zone has the same size area (16 pixels).

References[1] A. Bhattarai, K. T. Crampton, A. G. Joly, L. Kovarik, W. P. Hess, P. Z. El-Khoury, J. Phys. Chem. Lett., vol. 9, no. 24, 7105 (2018).
[2] J.-F. Bryche, R. Gillibert, G. Barbillon, P. Gogol, J. Moreau, M. Lamy de la Chapelle, B. Bartenlian, M. Canva, Plasmonics, vol. 11, no. 2, 601(2015).
[3] M. Sarkar, M. Besbes, J. Moreau, J.-F. Bryche, A. Olivéro, G. Barbillon, A.-L. Coutrot, B. Bartenlian, M. Canva, ACS Photonics, vol. 2, no. 2,237(2015).
[4] J.-F. Bryche, M. Vega, A. Tempez, T. Brulé, T. Carlier, J. Moreau, M. Chaigneau, P. G. Charette, M. Canva, Submitted to Nanomaterials

Novel integrated III-V/silicon AFM active optical probe for combined
AFM/NSOM/TERS measurements
Alexander A. Ukhanov, Fei-Hung Chu, Gennady A. Smolyakov, Kevin J. Malloy
Actoprobe LLC, 800 Bradbury SE, Suite 160, Albuquerque, NM 87106
E-mail: aukhanov@actoprobe.com

Actoprobe LLC has been developing a novel class of AFM active optical probes (AAOPs) fabricated entirely from
GaAs-based or similar semiconductor laser materials, including the semiconductor laser source, the cantilever with the
tip on its end, and the probe base, all monolithically integrated into a semiconductor chip for combined
AFM/NSOM/TERS measurements [1,2]. As important as it was for establishing the general concept of AAOP, thisapproach is not economical in utilizing relatively expensive III/V material, which makes the final product rather costly.
At the same time, in terms of their mechanical properties, GaAs-based cantilever AFM probes are typically inferior tostandard silicon cantilever AFM probes. To take full advantage of both the III/V semiconductor laser technology andthe established silicon microfabrication techniques of the standard technology of AFM tip/cantilever manufacturing,
we propose a novel concept of integrated III-V/silicon AAOP.
The innovation is accomplished by integrating a III-V semiconductor laser source into a silicon cantilever AFM probe
using a promising III-V silicon integration approach [3] based on metal bonding the III-V gain medium section to the
SOI silicon substrate for direct optical coupling (edge- or butt coupling) between the III-V gain section and the siliconlayer of the SOI waveguide (Fig. 1). The light is delivered to the end of the cantilever where it is redirected verticallyfrom the silicon waveguide into the probe tip using a folding mirror. The gold-coated tip acts as an output laser mirror
in the special intracavity design of the AAOP. The light reflected from the gold-coated tip is coupled back into thesilicon waveguide and, eventually in the laser chip active region. This light feedback mechanism has to be sufficiently
strong to make sure that the probe tip is supplied with intracavity high-intensity laser light.

Laser light coming outof the AFM tip
Si-based AFM probe

GaAs-based laser(QD with PBC )Fig. 1. Integrated III-V/silicon AAOP concept (left) and silicon-integrated AAOP with laser chip bonded to a silicon probe (right).

So far, a simpler concept of integrated III-V/silicon AAOP with free-space illumination of the probe tip has been
demonstrated. The concept is based on integrating a semiconductor laser source into a cantilevered silicon AFM probe
in such a way that the free propagating light from the integrated laser source can be used to illuminate the probe tip
and carry out AFM, NSOM, and TERS measurements. Using lithography and ICP dry etching, a standard silicon AFM
probe was patterned and etched to a depth of 150 µm to accommodate a thick laser chip with photonic-band-crystal(PBC) waveguide structure for improved vertical divergence [4]. The active region of the laser chip was aligned withthe probe tip, so that the free propagating light from the integrated laser source was used to illuminate the probe tip
and carry out AFM and NSOM measurements.
In conclusion, we have proposed a novel concept of integrated III-V/silicon AAOP that takes full advantage of boththe III/V semiconductor laser technology and the established silicon microfabrication techniques of the standard
technology of AFM tip/cantilever manufacturing. The first prototype of integrated III-V/silicon AAOP with free-space
illumination of the probe tip has been demonstrated with confirmed AFM and NSOM performance.
References[1] Ukhanov, A. A., Smolyakov, G. A., “Atomic force microscopy active optical probe”, Patent No. US 9482691, issued November 01, 2016.
[2] Ukhanov, A. A., Smolyakov, G. A., Chu, F. H., Wang, C., “Monolithic atomic force microscopy active optical probe”, Patent No. US
11,016,119, issued May 25, 2021.
[3] Creazzo, T., Marchena, E., Krasulick, S. B., et al. 2013. Opt. Express 21, 28048-28053.
[4] Liu, L., Qu, H., Liu, Y, et al. 2014. Appl. Phys. Lett. 105, 231110.

Infrared nano-spectroscopy of antenna coupled intra-molecular vibrational
interactions and dynamics
Jun Nishida1,†, Roland Wilcken1,†, Johan F. Triana2, Aurelian John-Herpin3, Hatice Altug3, Felipe Herrera2,4,
and Markus B. Raschke1,*
1. Department of Physics and JILA, University of Colorado, Boulder, 2000 Colorado Ave, CO 80309, USA
2. Department of Physics, Universidad de Santiago de Chile, Av. Victor Jara 3493, Santiago, Chile
3. Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerland
4. ANID-Millennium Institute for Research in Optics, Chile
E-mail: *markus.raschke@colorado.edu †: These authors contributed equally

Intramolecular vibrational coupling and energy transfer in polyatomic molecules not only defines nuclear motion
during chemical processes but is also the fundamental limit to vibrational coherence. Intramolecular coupling can be
resolved by two-dimensional infrared (2D-IR) spectroscopy. However, with diffraction-limited cavity mode volumes
and probing large heterogeneous molecular ensembles, the approach precludes a controlled modification of coupledvibrational coherence in small molecular ensembles as desirable for, e.g., new photochemical pathways.
To address this outstanding challenge, we pursue selective modification of the intrinsic intramolecular vibrational
coupling and energy transfer by extrinsic antenna coupling of molecular vibrations. In femtosecond infrared nanospectroscopy of molecular-monolayer functionalized length-tunable IR-resonant nano-wire antennas we resolve
vibrational coupling with sensitivity down to 10’s of molecules. Exemplary, we use a metal organic complex
Re(bpy)(CO)3Cl (bpy = 2,2’-bipyridine) surface bound by click-chemistry (Fig. 1a) with its three long-lived CO
asymmetric v̅A’(2) = 1900 cm-1 and v̅A’’ = 1940 cm-1 (spectrally unresolved), and symmetric v̅A’(1) = 2020 cm-1 stretch
modes [1,2] (Fig. 1b). Tuning the antenna resonance across the vibrational modes, on resonant excitation of thesymmetric stretch A’(1) with v̅ant = v̅A’(1), the signal amplitude increases and yhe lifetime T2(v̅A’(1)) is reduced from
760 fs to 300 fs (Fig. 1 c,e) due to Purcell enhancement as described previously [3,4]. Significantly, we also observea reduction in T2(v̅A’(1)) by tuning the nanoantenna on resonance with A’(2) and A’’ (Fig. 1e). This behavior is a direct
signature of intramolecular vibrational coupling and energy transfer. We model the results based on a semi-empiricalquantum approach we recently developed [5] to describe the multispectral interplay between antenna-mediated andintramolecular coupling strength gl (see Fig. 1d). We further observe spatial variations in T2(ṽA’(1)) depending on tipantenna position (data not shown), which we model as interfering pathways of vibrational coherence.
In conclusion, vibrational mode-selective infrared nanoantenna coupling can resolve intramolecular interaction andenergy transfer in linear spectroscopy – information otherwise only accessible through coherent 2D spectroscopy.

Fig. 1. (a) IR resonant nanoantenna coated by a monolayer of a Re-metal carbonyl complex to investigate the intra- and antennamediated vibrational energy transfer by nano-probe spectroscopy. (b) Scheme of the CO stretch modes and the laser and antenna
frequencies. (c) Relative lifetime of the vibrational to the antenna signal. (d) Calculated T2 lifetime of the A’(1) mode withchanging antenna resonance in dependence on the intramolecular coupling gl. (e) Measured T2 lifetime of the A’(1) mode

References[1] C. Yan et al., “Unraveling the dynamics and structure of functionalized self-assembled monolayers on gold using 2D IR spectroscopy and MD
simulations”, PNAS. 2016, 113, 4929–4934. [2] L. M. Kiefer et al., Acc. Chem. Res. 2015, 48, 1123-1130. [3] B. Metzger et al., “PurcellEnhanced Spontaneous Emission of Molecular Vibrations”, Phys. Rev. Lett. 2019, 123, 153001. [4] E. A. Muller et al., “Nanoimaging andControl of Molecular Vibrations through Electromagnetically Induced Scattering Reaching the Strong Coupling Regime”, ACS Photonics 2018,
5, 3594–3600. [5] J. F. Triana et al., “Semi-empirical Quantum Optics for Mid-Infrared Molecular Nanophotonics”, arxiv:2110.07371, 2021

Intraparticle Heat Transfer inside Cross-shaped Nanoparticles
Revealed by Femtosecond Transient Spectroscopy
M. Vega1,2, JF Bryche1, P. Bresson1,2, PL Karsenti1, M. Besbes2, J. Moreau1,2,
P. Gogol1, D. Morris1, P.G. Charette1, M. Canva1,2,
1. Laboratoire Nanotechnologies Nanosystèmes (LN2 – IRL 3463) – CNRS/ Institut Interdisciplinaire d’Innovation Technologique(3IT) /Université de Sherbrooke, Sherbrooke, Canada.
2. Laboratoire Charles Fabry (LCF), Université Paris-Saclay, Institut d'Optique Graduate School, CNRS, Palaiseau, France.
E-mail: marlo.vega@usherbrooke.ca

Nanoparticles (NP) can release the energy absorbed under light excitation into heat. To fully exploit these heatnanosources in applications such as medicine, catalysis or photonic switch, the dynamics of heat distribution inside
NPs must be better understood and modelled. It remains a challenging task regarding the time and space scales involvedin the photothermal process (femtosecond and nanometer scales).
In this work, we realized femtosecond transient spectroscopy measurement on cross-shaped gold nanoparticles andthen compared the data with our extended two-temperatures model [1]. This NP geometry is known to support
polarization-dependent localized plasmonic resonances (LSPR) along each branch. By selectively exciting one LSPR,
a single branch can be heated, with the energy carried by non-thermalized electrons and electron-phonon coupling tothe other branch in a few 100 fs. The thermal distribution inside the cross-shaped NP can be determined by measuring
the time delay between the shifts in spectral responses in each branch. In addition, the spatiotemporal dynamics of theelectronic and lattice temperatures inside the NP can be determined by fitting the experimental data to the numericalmodel. Good agreement was found between simulations and experiments.
The pump-probe setup is based on a Ti-sapphire femtosecond (~75 fs HWHM) laser centered at 795 nm. The pumpfrequency is tuned through an OPA to a wide range of wavelengths from the UV to the IR. A fraction of the 795 nm
laser source is sent through a non-linear crystal to generate the white light continuum probe. The samples consist of gold
crosses fabricated by E-Beam lithography on a 30 nm gold film, atop a 2 nm titanium adhesive layer and BK7 substrate.
The dimensions of the crosses are: 300/410 nm branch lengths, 60 nm height, 60 nm width and 520/640 nm period along
the short/long branch axes.
An illustration of the optical excitation configuration is shown in Figure 1.a. The pump is used to resonantly heatone branch of the cross and the probe to measure the optical responses of both branches. Figure 1.b shows a simulationof the resulting electronic temperature (Te) reached inside the nano cross a few femtoseconds after the excitation,
where the asymmetric electronic temperature distribution inside the cross can be seen. Figure 1.c shows the measured
optical response delay between the longitudinal and transverse LSPR.

Fig. 1. a) schema of the pump-probe experiment on gold cross-shaped nanoparticles. b) Numerical simulation of the electronic
temperature distribution inside the nanoparticles at 300fs after the pulsed light excitation. c) Spectral profiles of ΔR/R for each
LSPR associated to each branch.

To go further, we then exploit this mechanism through reversible polarization control to manage heat repartition
and time delay inside the nanoparticle.
References[1] Bresson, P. et al., “Improved two-temperature modeling of ultrafast thermal and optical phenomena in continuous and nanostructured metal
films,” Phys. Rev. B, vol. 102, no. 15, Oct. 2020.

Correlation effects of electrons emitted from needle tips
by strongly confined ultrashort optical pulses
Stefan Meier, Jonas Heimerl, Peter Hommelhoff
Department of Physics, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Staudtstraße 1, 91058 Erlangen, Germany, EU
E-mail: stefan.m.meier@fau.de

Optical field enhancement on metallic nanostructures allows the measurement of nonlinear light-matter interactions
with moderate laser pulse intensities. In the case of metal needle tips, strongly confined optical near-fields at the tip
apex allow triggering ultrashort electron emission by few-cycle laser pulses. Measuring the resulting kinetic energy ofthese electron pulses enables deep insights in the nonlinear emission process in combination with the subsequent
electron dynamics of the electron in the optical near-field. Thus the electron energy spectra intrinsically serve as probe
for the optical near-field at these tips [1]. These processes have been well investigated within the past decade. For
example, the quenching of the electron quiver motion in the near-field has been shown by the laser wavelength
dependence of the electron spectra [2]. By taking advantage of the carrier-envelope phase of the optical laser field, theelectron emission can even be controlled on the attosecond timescale [3].
Besides the fundamental insights gained on light-matter interactions, the resulting electron pulses exhibit excellent
properties to serve in ultrafast electron devices. We could recently show that the spatial coherence of such an electron
beam is as good as its DC equivalent, namely field-emitted electrons from the same tip [4]. In the present study, we go
one step further and investigate the spatial coherence properties as function of the average number of electrons per
pulse. As the electrons are highly confined in space and time when they are emitted, they are interacting with eachother by Coulomb interaction [Fig. 1 (a)]. We show an exponential decrease in the visibility of electron interference
measurements [Fig. 1 (b)] depending on the number of emitted electrons per pulse. Example electron interference
images are shown in Fig. 1 (c) and 1 (d). The observed reduction of spatial coherence corresponds to an increase ineffective source size, as supported by numerical point-particle simulations [5]. We will discuss the implications forimportant ultrafast electron beam properties.

Fig. 1 (a) Illustration of a metal tip with an optical near-field that is triggering the emission of multiple electrons. The electronsinteract via Coulomb interaction. (b) Sketch of the experimental setup: few-cycle laser pulses are focused on a biased tungsten
needle tip. The resulting electron pulses are passing by a carbon nanotube (CNT), acting as an electrostatic biprism. The electron
wave packets interfere and are detected at a micro-channel plate (MCP). (c) Interferogram of the electron beam at low numberof electrons per pulse. (d) Interferogram at more than one electrons per pulse. Due to Coulomb interactions, the contrast of theinterference pattern is reduced.

References[1] Thomas, S., Krüger, M., Förster, M., Schenk, M., Hommelhoff, P.. Probing of optical near-fields by electron rescattering on the 1 nm scale.
Nano Letters 13, 4790 (2013)[2] Herink, G., Solli, D. R., Gulde, M., Ropers, C.. Field-driven photoemission from nanostructures quenches the quiver motion. Nature 483, 190193 (2012)[3] Krüger, M., Schenk, M., Hommelhoff, P.. Attosecond control of electrons emitted from a nanoscale metal tip. Nature 475, 78-81 (2011)[4] Meier, S., Higuchi, T., Nutz, M., Högele, A., Hommelhoff, P.. High spatial coherence in multiphoton-photoemitted electron beams. Applied
Physics Letters 113, 143101 (2018)[5] Meier, S. Hommelhoff, P.. Manuscript under review.