bluuebunny/crossref_metadata_2025 huggingface dataset:
Clinical and economic benefits of the Intellispace Portal applications CT TAVI and Spectral CT: Findings from a two-step Delphi panel
Authors: Veillet-Chowdhury Mahdi , Harvey James E. , Wang Peter S. , Panda Saswat , Connolly Mark , Mesarosh Marlene A. , Medic Goran , Beth Jiwan , Wiegand Bodo , Danrad Raman
Published: February 2020

Background: IntelliSpace Portal (ISP) is an advanced visualization platform that offers a single integrated solution designed to help physicians work more efficiently. This study aimed to develop a consensus statement on the clinical and economic benefits of two Intellispace Portal (ISP) applications (computed tomography (CT) transcatheter aortic-valve implantation (TAVI) and Spectral CT) applications.

Methods: A modified Delphi method of two rounds of queries was used in a panel of 17 experts (11 for Spectral CT and 8 for CT TAVI). The experts were identified via referral and selected to achieve a balanced representation of subject matter experts. The Delphi process was conducted online using the MESYDEL platform. Two rounds of Delphi queries were conducted between July 22 and October 14, 2019. All data was collected prospectively.

Results: Areas of consensus represented contribution of ISP applications toward quadruple aim goals. Consensus was reached that the Spectral CT application led to more confident decision making, improved diagnosis capabilities leading to better treatment paths, and a better work experience. Panelists noted that they required fewer tests to make a diagnosis using Spectral CT. The majority of physicians (63%) agreed that CT TAVI led to time savings for ‘device sizing’ results, and 75% of physicians agreed that the tool resulted in a better work experience.

Conclusions: The increased diagnostic confidence of spectral information could eliminate the need for many follow-up scans in patients, resulting in clinical benefit to the patient in terms of reduced exposure to radiation and economic benefit to healthcare systems in reducing the number of additional scans. The staff satisfaction goal of the quadruple aim is also satisfied by Spectral CT and CT TAVI leading to a better work experience in our panelist physicians. This may result in indirect benefits such as reduced rates of physician burnout and greater provider satisfaction.
An evaluation of a personalised text message reminder compared to a standard text message on postal questionnaire response rates: an embedded randomised controlled trial
Authors: Cochrane Ann , Welch Charlie , Fairhurst Caroline , Cockayne Sarah , Torgerson David J. ,   OTIS Study Group
Published: February 2020

Background: Research outcome data is commonly collected using postal questionnaires; however, poor response can introduce bias and reduce statistical power. Text messaging is simple, cost-effective, and can be customised to the individual. Personalised, reminder text messages may improve response rates.

Methods: A two-arm, parallel group ‘Study within a Trial’ (SWAT) was embedded within the Occupational Therapist Intervention Study (OTIS), a randomised controlled trial of a home assessment for falls prevention in older people.  OTIS participants who provided a mobile phone number were randomly allocated (1:1) to receive either a personalised text message (Title, Surname, plus York Trials Unit (YTU) text) or the standard YTU text alone, prior to receiving their four-month post-randomisation follow-up postal questionnaire. The primary outcome measure was the proportion of participants who returned the questionnaire. Secondary outcomes were: time to response, completeness of response, requirement of a reminder letter, and cost-effectiveness. Binary data were compared using logistic regression and time to response by Cox proportional hazards regression.

Results: A total of 403 participants were randomised: 201 to the personalised text and 202 to the standard text.  Of the 283 participants included in the final analysis, 278 (98.2%) returned their questionnaire; 136 (97.8%) for the personalised text versus 142 (98.6%) for the standard text (adjusted odds ratio 0.64, 95% CI 0.10 to 3.88, p=0.63).  The median time to response was nine days in both groups.  In total, 271 (97.5%) participants returned a complete questionnaire; 133 (97.8%) in the personalised text versus 138 (97.2%) for the standard text.  In total, 21 reminder letters were sent. The additional cost of personalised text messages was £0.04 per participant retained.

Conclusions: Personalised texts were not superior to standard texts in any outcome assessed in our study. Further SWATs are needed to perform a meta-analysis and obtain more evidence.

Registration: ISRCTN22202133; SWAT 35.
Experimental study of the influence of pulse electrophoresis of blood plasma 0 (I) on healing of wounds and formation of normotrophic scars in laboratory animals
Authors: Terekhov G. , Chuhraeva E. , Kostylev M. , Galich S. , Savitskaya I. , Zukow W. , Kamalov R. , Knyazeva I.
Published: February 2020

In experimental study confirmed the acceleration of wound healing and forming normotrophic scars tissue in laboratory animals using the transdermal administration of blood plasma 0 (I) by pulsed electrophoresis under the influence of an external magnetic field. It was established that the method proposed by the authors prevents the development of hypertrophic and keloid scars, and also stimulates tissue regeneration in the surgical area due to the activation of local regeneration processes.
Integrated microwave photonic filters
Authors: Liu Yang , Choudhary Amol , Marpaung David , Eggleton Benjamin J.
Published: February 2020

Microwave signal filtering is a fundamental and central functionality in radio-frequency (RF) systems. Underpinned by advanced integrated photonics technologies, emerging integrated microwave photonic (IMWP) filter platforms enable reconfigurable and widely tunable RF signal filtering functionalities that were unattainable using conventional electronics while also exhibiting superior features in terms of compactness, light weight, stability, low power consumption, and low latency. This paper presents a comprehensive review of the principles, architectures, and performance of IMWP filters. We highlight recent advances of IMWP filters enabled by on-chip nonlinear optics, RF-interference technology and emerging integration platforms, with an emphasis on the RF performance which is critical for their usability in real-world applications. We conclude with a perspective on future research challenges and new possibilities for IMWP filters.
Laser-induced fluorescence of 1CH2 produced in the decomposition of propylene oxide
Authors: Grant E. R. , Chou J.-S. J. , Adams T. E.
Published: February 2020

In this paper we wish to report a new unimolecular dissociative source of methylene. The subject of our investigation is propylene oxide, which is a prototypical alkyl epoxide important for its relevance in air pollution and stratospheric systems as an oxygen atom olefin-addition product. Our findings on the mechanism of its decomposition are worthy of particular note in light of the fact that carbene elimination has not previously been associated with hydrocarbon epoxide decomposition.
Trace gas detection at atmospheric pressure using tunable diode lasers
Authors: Cassidy D. T. , Reid J.
Published: February 2020

Tunable diode lasers (TDL) are widely used for the detection of trace gases and pollutants in the atmosphere. In many of these applications, the gas sample flows through a multipass cell at reduced pressure (~30 Torr), and the resulting narrow IR absorption lines can be detected with very high sensitivity. Infrared absorptions of 1 part in 105 can be observed over path lengths of 100 m, giving noise levels equivalent to absorption coefficients of 10−7 m−1.
Computer-automated CO2 laser long-path absorption system for air quality monitoring in the working environment
Authors: Persson U. , Lundqvist S. , Eng S. T.
Published: February 2020

The hazardous gaseous substances produced in connection with many important industrial processes are today an increasing problem in the working environment, Remote measurements of many of these substances can be made using differential absorption of CO2 laser radiation, which is now a well-established technology.1–3
Ultraviolet-laser excitation of color-center lasers
Authors: Litfin G. , Welling H.
Published: February 2020

Nitrogen and excimer lasers are among the most reliable and powerful pump sources for excitation of pulsed tunable lasers. These lasers are powerful and in the case of excimer lasers provide high output energies with a short pulse length. Therefore, in many experiments using tunable lasers these pump sources have been used for the investigation of nonlinear processes or time-resolved studies.
Laser monitoring of fog and test aerosol concentrations
Authors: Carlon Hugh R. , Kimball D. V. , Wright R. J.
Published: February 2020

Two laser techniques for monitoring aerosol droplet mass concentration are described. Both techniques utilize Mie calculations of optical extinction by droplets of liquids for which optical constants are known, which are shown to be experimentally verifiable. One technique utilizes a He-Ne laser1 in the geometric scattering regime,2 where very simple functional relationships are shown to exist between droplet extinction and diameter.
Use of laser beam atmospheric refraction for remote lapse rate sensing
Authors: Porch W. M.
Published: February 2020

Atmospheric refraction of laser beams over complex terrain has been successfully applied to measure the spatially averaged air temperature lapse rate. The lapse rate γ, defined as the rate of decrease in temperature with height, remains an important atmospheric parameter for predicting turbulent diffusion within the boundary layer and in studying urban heat island and pollution levels.1 The noise due to small-scale temperature variability makes the lapse rate difficult and expensive to measure on a spatial scale applicable to numerical meteorological modeling.
Stabilized superresolution in photon correlation laser anemometry
Authors: Abbiss J. B. , Dhadwal H. S.
Published: February 2020

Conventional signal and image processing techniques are limited in resolution by the bandwidth or aperture of the encoding device; in optical terms, this resolution is set by the diffraction limit, as defined by the Rayleigh criterion. The information retrievable from the signal is thus inherently restricted, even at low noise levels. In recent years a number of techniques for overcoming this limitation and achieving superresolution have been proposed; among these, the iterative extrapolation procedures which exploit a priori information, such as known signal constraints, have been extensively studied.
Laser-plasma x rays for laboratory EXAFS
Authors: Epstein H. M. , Schwerzel R. E. , Campbell B. E.
Published: February 2020

Extended x-ray-absorption-fine-structure (EXAFS) is a tool of increasing importance for studying the structure of materials at the atomic level. EXAFS provides information on the identities and spatial arrangement of the atoms in solids, liquid or gas. In the EXAFS technique, the x-ray absorption coefficient of a material is measured as a function of energy above a K or L edge. The fine structure in this spectrum yields information on the distances of neighboring atoms. A very intense, high-brightness x-ray source is required for practical EXAFS. The energy range corresponding to K or L edges of atoms with atomic numbers up to 40 is 1/2 to 3 keV. This energy range is well suited to laser-plasma x-ray sources.1,2
Measurement and control of subangstrom displacement by acoustooptical techniques
Authors: Wang C. P. , Varwig R. L. , Ackman P. J.
Published: February 2020

Control of laser mirror spacing and angular orientation is very important for laser frequency and mode stability. Interferometric methods have been used to measure such small displacements. For example, using a Mach-Zehnder interferometer, a stable He-Ne laser, and a frequency counter, submicrometer displacement can be measured. Because the Mach-Zehnder interferometer is very sensitive to mechanical vibration and misalignment, this technique is rather difficult, and expensive equipment, such as stable lasers and fast counters, is needed.
Two-photon laser
Authors: Toschek P. E. , Nikolaus B.
Published: February 2020

With the general n-photon interaction of atoms (molecules) and light, the energy

W
=

∑
i

∑

n
l

ℏ

ω
i

n
l

(

with
 
n
=

∑

n
l

|

n
l

|

)

is exchanged, if there is resonance W =ħω0 with a term difference ω0 of the particles. This process provides for gain if an emittive step (any n
k
< 0) is involved. Aside from single-photon emission, stimulated Raman emission (ω1–ω2 = ω0) is the basis for light sources of unique characteristics.
Connecting conductors on semiconductor devices by lasers
Authors: Hongo Mikio , Miyauchi Tateoki , Yamaguchi Hiroshi , Masuhara Toshiaki , Minato Osamu
Published: February 2020

Progress in improvement in size and density of semiconductor memory devices has been astonishing in recent years. Redundancy techniques are indispensable to improve product yield in which defective memory cells, when discovered, are replaced by spare cells. This replacement is performed by programming on-chip devices. So far, laser cutting1 or electrical conductor (fuse) cutting2 has been used. However, these methods damage the passivation layers. A conductor connecting technique by laser irradiation is being developed so that a new redundancy technique3 can be used.
Spatial period division using an ArF laser
Authors: Hawryluk A. M. , Smith Henry I. , Osgood Richard M. , Erhlich D. J.
Published: February 2020

Spatial period division1-3 is a lithographic technique in which a pattern of spatial period P/m is exposed by the diffraction field of a mask having a spatial period P. We have used an ArF laser (λ= 193 nm) and a mask of spatial period 199 nm to expose a 99.5-nm period grating pattern in PMMA.
High-speed UV- and x-ray-sensitive InP photoconductive detectors
Authors: Deutsch Thomas F. , Leonberger Fred J. , Foyt A. G.
Published: February 2020

Indium phosphide (InP) optoelectronic-switch structures are shown to be fast broadband photon detectors having a spectral response extending from the near IR to the x-ray region. These InP switches, similar to the original Si devices made by Auston,1 have been shown to have high sensitivity in the 500-800-nm spectral region.2,3 The pulse response is ~1 nsec for the devices made as described below but can be <100-psec FWHM with appropriate fabrication.2,4 Because these devices are based on surface photoconductivity and because the surface recombination velocity for electrons can be small in InP, the useful spectral range would be expected to extend to photon energies many times the band gap energy of InP. In addition, the high Z number of InP suggests that these devices should also be sensitive x-ray detectors.
Laser saturated fluorescence measurements of OH concentration arid rotational temperature in flames
Authors: Lucht Robert P. , Sweeney Donald W. , Laurendeau Normand M.
Published: February 2020

Laser saturated fluorescence1 is a promising technique for sensitive, accurate, and spatially resolved measurements of the concentrations of flame radicals such as OH. Such radicals play an important role in flame chemistry and pollutant formation.
High-capacitance parallel-resonant rf-excited waveguide CO2 lasers
Authors: Chenausky Peter P. , Hart Richard A. , Newman Leon A , Hoffman Nelson N.
Published: February 2020

Radio-frequency excitation of waveguide CO2 lasers is proving to be a versatile technique which lends itself readily to a variety of discharge geometries such as longitudinally segmented,1 transversely pulsed,2 and a low-capacitance highly efficient device.3 The relatively short period of time required to develop a long-lived device is particularly impressive.3 In contrast to the conventional dc- excited lasers,4 the rf-excited devices have low voltage discharge arrangements and hence tend to be highly rugged by virtue of the diversely employed metallic vacuum envelope.5
Stable sealed transition-selective CO2 laser at room temperature
Authors: Peters P. J. M. , Witteman W. J.
Published: February 2020

For many applications the CO laser with a great number of vibrational-rotational transitions in the 4-6-µm wavelength region is an attractive device. The large-scale acceptance of this device, however, is seriously hindered by its complexity, and in case an intracavity grating is used there is only a small part of the spectrum (close to the blazing angle) for which high reflectivity Is obtained, white in essence the system requires high optical quality. Further-more, up to now most devices are flowing systems and operate to obtain tens of watts at liquid nitrogen temperature.
Materials limitations on the characteristics of the microchannel spatial light modulator
Authors: Warde Cardinal
Published: February 2020

The microchannel spatial light modulator (MSLM)1 is a versatile, highly sensitive, optically addressed device being developed for low-light-level real-time optical information processing. In addition to real-time operation, it can be designed to exhibit simultaneously long-term (months) optical-information storage.
High resolution techniques tor adaptive phase compensation
Authors: Fisher A. D. , Warde Cardinal
Published: February 2020

High resolution adaptive optical systems containing millions of spatial resolution elements are under development for real-time wave front correction in such applications as1-3 atmospheric optical communications and imaging and high energy laser propagation. Unlike the previous technology, consisting of discrete phase estimators hard-wired to phase modulator arrays, an all-optical parallel processing approach is being pursued. In operation, wave front spatial phase distortions are transformed by an all-optical phase estimator into intensity variations in a control beam. This control beam drives a monolithic optically addressed spatial phase modulator to straighten out the corrupted wave front.
Picosecond optical pulse generation in stripe-geometry lasers with a short passive region
Authors: Chen Y. C. , Zory P. S.
Published: February 2020

There has been considerable interest in the dynamic characteristics of semiconductor lasers with deliberately introduced saturable absorbers because of their usefulness in ultrashort optical pulse generation, optical switching, and mode locking. The methods of introducing controllable saturable absorption include multisegment lasers,1-3 proton bombardment,4 and inhomogeneous excitation.5 In this report, we describe a simple device structure for picosecond optical pulse generation that utilizes the edge light emitting diode (ELED) type of configuration with a short passive region, as shown in Fig. 1.
Turning off the vacuum: inhibited spontaneous emission
Authors: Kleppner Daniel
Published: February 2020

Spontaneous emission plays a fundamental role in all radiative processes. It limits the lifetime of excited atoms, causing basic uncertainty in their energies. It sets the scale for absorption and stimulated emission, providing a natural scale for the coupling of matter and radiation. It is the ultimate source of noise in nature. Spontaneous emission is such a ubiquitous process that its occurrence is generally taken for granted. In principle, however, spontaneous emission can be altered, either enhanced or inhibited, allowing one to modify primary radiative processes. Experimental techniques are available for realizing these possibilities, and a new area of radiative phenomena is opening for study.
Sealing properties of the plasma recombination laser
Authors: Bohn W. L. , Schall W.
Published: February 2020

Although laser action has been reported1 in single-and multiple-charged recombining ions, no attempt has been made to establish valuable scaling relations to address the potential of the recombination laser with respect to the specific energy attainable at short wavelengths.
X-ray backlighting characterization experiments performed with laser wavelengths of 1.06, 0.53, and 0.35 µm
Authors: Matthews D. L. , Attwood David T. , Campbell E. M. , Ceglio N. , Coleman L. W. , Hermes G. , Kauffman R. , Koppel L. , Lee R. , Manes K. R. , Rupert V. , Slivinsky V. , Turner R. E. , Ze F.
Published: February 2020

This is a second-generation report on the characterization of laser-produced x-ray backlighting line sources. Previous work1-3 concentrated on the production of Au M(~2.5-keV), Ti K(~4.75-keV), Ni K (7.7-keV), and Zn K(8.6-keV) lines as a function of laser pulse length and intensity at λ
L
= 1.06 and 0.53 µm. Yaakobi et al.4 recently reported a similar characterization of K x-ray line emitters. They note that a factor of 10 or more increase in the line production efficiency (compared to λ
l
= 1.06-µm data) can be obtained when using a laser of wavelength λ
L
=0.35 µm. With the exception of lines from Au M band radiation, our present work does not substantiate their result. We observe a significantly less increase in production efficiency as a function of decreasing laser wavelength.
Self-injected laser for high-power short- pulse generation
Authors: Brito Cruz C. H. , De Martini F. , Mataloni P. , Palange E.
Published: February 2020

Adiabatic pulse compression by a large factor (~10) has been achieved simply and reliably in conventional lasers by suitable driving of the cavity Q-factor with a Pockels cell (PC), This is the effect of an unconventional technique of self-injection (or cavity flipping).1,2
Miniature sealed CO2 TEA lasers with Integral semiconductive preionization
Authors: Pace Paul , Mathieu Pierre , Cruickshank James
Published: February 2020

Since discovery of the transverse excitation of atmospheric-pressure CO2 lasers, several techniques have been developed to produce high-pressure glow discharges. Among the simplest and most compact devices, UV radiation is used to condition the gas before and/or during the discharge. In most types of device the UV radiation is produced by a separate discharge such as by trigger wires or separate UV sources. These constaints have generally had a significant effect on the size, cost, and performance characteristics of these devices.
Carbon dioxide temperature saturation
Authors: Smith A. L. S. , Mellis J.
Published: February 2020

With increasing discharge excitation, saturation and subsequent reduction of the gain and oscillation output power in cw and TE CO2 lasers have frequently been observed, Ballik et al.1 have shown that this cannot be completely accounted for by discharge deterioration and gas heating effects, Davies et al.
2
sought to show that such output reduction is explained by overpumping of the CO2 to very high values of the v3(OO0n) mode vibrational temperature T3 beyond the optimum value for 00°1 level population (~4500 K).
In situ laser spectroscopic detection of species related to CVD and plasma etching of III–V compound semiconductors
Authors: Donnelly V. M. , Karlicek R. F. , Flamm D. L. , Johnston W. D.
Published: February 2020

Chemical vapor deposition (CVD) techniques are used throughout the semiconductor industry to fabricate multiple-layer device structures. For example, in the expitaxial deposition of InP,1 indium is transported in the form of InCI [formed in the high temperature reaction of ln(
I
) with HCI], while phosphorus impinges on the substrate surface as a mixture of PH3, P2, and P4 (formed in the pyrolysis of PH3).
Generation of hyper-entangled photons in a hot atomic vapor
Authors: Wang Chengyuan , Lee Chung-Hyun , Kim Yosep , Kim Yoon-Ho
Published: February 2020

A source of hyper-entangled photons plays a vital role in quantum information processing, owing to its high information capacity. In this Letter, we demonstrate a convenient method to generate polarization and orbital angular momentum (OAM) hyper-entangled photon pairs via spontaneous four-wave mixing (SFWM) in a hot

87

R
b

atomic vapor. The polarization entanglement is achieved by coherently combining two SFWM paths with the aid of two beam displacers that constitute a phase self-stabilized interferometer, and OAM entanglement is realized by taking advantage of the OAM conservation condition during the SFWM process. Our hyper-entangled biphoton source possesses high brightness and high nonclassicality and may have broad applications in atom–photon-interaction-based quantum networks.
Observation of Townes soliton formation
Authors: Moll K.D. , Gaeta Alexander L.
Published: February 2020

Nonlinear wave collapse is an inherent phenomenon to several areas of physics including hydrodynamics, plasma physics, and nonlinear optics. In the latter case, the process responsible for collapse is the self-focusing of light in a medium with an intensity-dependent refractive index. The nature of the collapse has been theoretically analyzed using a variety of techniques including the variational principle [1], modulation theory [2], and numerical simulations [2,3]. Although the technique based on the variational principle is simple to apply, the other techniques have demonstrated that the collapse dynamics are too complicated to be fully captured by the ansatz that the beam maintains a Gaussian profile. In particular, modulation theory and numerical simulations predict that regardless of the shape of the input beam profile a collapsing beam transforms its radial profile into a focused Townes soliton. In this report, we present experimental evidence demonstrating that the spatial profile of a collapsing femtosecond laser pulse does indeed evolve into the cylindrically symmetric profile described by the Townes soliton for the case in which the input beam is either elliptically or irregularly shaped. These results could lend further understanding to recent experiments [4] that have observed extended light filaments in air with femtosecond laser pulses.
Controlling the Dephasing of Vibrational Wavepackets in Potassium Dimers
Authors: Walmsley Ian , Londero Pablo , Wallentowitz Sascha , Waxer Leon , Radzewicz Czeslaw
Published: February 2020

We have controlled vibrational wavepacket dephasing in potassium dimers using an AOM pulse shaper which is run by a learning algorithm. Several decoherence-resistant excitation subspaces are presented. We include a model for interpreting the wavepacket evolution.
Long term (>500 seconds) phase coherence of a train of ultrashort pulses
Authors: Fortier T.M. , Jones David J. , Ye J. , Cundiff S.T. , Windeler R.S.
Published: February 2020

Following the recent demonstrations [1-4] of stabilizing the relative pulse-to-pulse phase between the carrier wave and the pulse envelope (carrier-envelope phase) generated by mode-locked femtosecond (fs) lasers, effort has focused on measuring and increasing the coherence time of this phase stability. Carrier-envelope phase stabilization is an important advance for fs technology, as the advent of few-cycle pulses makes it possible to study processes that are directly sensitive to the electric field of each pulse, rather than just the intensity envelope [5,6]. In order for most of these physical processes to be experimentally investigated, it is of interest to extend the time period (i.e., the coherence time) over which phase coherence of the carrier-envelope phase is maintained. By stabilizing the output of 10-fs mode-locked laser, we have increased the carrier-envelope phase coherence of the emitted pulse train from 1 ms [3] to greater than 500 seconds.
Core-Level Photoemission Spectroscopy : Kinetics of Cluster Formation During Femtosecond Laser Ablation
Authors: Glover T.E. , Ackermann G.D. , Belkacem A. , Heimann P.A. , Hussain Z. , Padmore H.A. , Ray C. , Schoenlein R.W. , Steele W.F.
Published: February 2020

We report, to our knowledge, the first use of pump-probe photoemission spectroscopy to study core-level dynamics during a laser-driven phase transition. Synchrotron x-rays probe the kinetics of cluster formation during the initial moments of femtosecond laser ablation.
Ultrafast elementary events in the excited state of wild-type green-fluorescent protein
Authors: Winkler Kathrin , Seidel Marco , Vöhringer Peter
Published: February 2020

The optical response of wild-type green-fluorescent protein (GFP) has been measured at room temperature following 40-fs, 400-nm photoexcitation. In the spectral range of the stationary fluorescence of GFP, delayed emission due to excited-state proton transfer (ESPT) can be induced. The entire spectro-temporal response is simulated quantitatively using a novel dynamical model which includes an energy-dependent rate constant for ESPT, intra- and intermolecular flow of vibrational energy, and an additional non-radiative decay pathway leading to internal conversion.
Exploring sub-picosecond dynamics in the far-infrared with THz spectroscopy
Authors: Schmuttenmaer Charles A. , Beard Matthew C. , Turner Gordon M.
Published: February 2020

Time-resolved THz spectroscopy has been used to characterize the time-dependent photoconductivity in a variety of semiconductors, ranging from bulk GaAs to colloidal sintered TiO2. It has also been used to directly measure sub-picosecond intramolecular electron transfer.
THz Emission from Charge-Transfer Reactions in Molecules Aligned in Solutions and Crystals
Authors: Carey John J. , Jones David , Jamison Steven P. , Wynne Klaas
Published: February 2020

A detailed experimental and theoretical study of THz pulse generation by photoinduced charge transfer in solution and crystals will be presented. In addition, a novel class of molecular crystals will be introduced with optical rectification efficiency superior to ZnTe.
Making and Measuring Vibrational Wave Packets In Small Molecules
Authors: Weinacht T. C. , Bartels R. A. , Leone S. R. , Murnane M. M. , Kapteyn H. C.
Published: February 2020

We present results demonstrating the creation, control and measurement of multimode vibrational wave packets in the electronic ground state of small polyatomic molecules1. The wave packets are created using non-resonant impulsive Raman scattering, which allows for excitation of a large class of molecules. The excitation of ground state wave packets yields information of relevance to chemical reactions, which occur largely in the electronic ground state.
Efficient Frequency Conversion From a Novel QPM Semiconductor Waveguide Crystal
Authors: Rafailov E. U. , Loza-Alvarez P. , Artigas D. , Sibbett W.
Published: February 2020

Recent progress in the development of electric-field poling techniques for the patterning of the domain structure of ferroelectric materials has enabled the implementation of distinctive quasi-phase-matched (QPM) structures for efficient nonlinear optical interactions [1]. Such QPM devices have been fabricated in LiNbO3, LiTaO3 and in the KTP-family crystals. Semiconductor materials which have larger nonlinear coefficients (χ
(2)
), are also promising candidates for efficient frequency up/down conversion. However, the technology employed at present to fabricate semiconductor QPM devices suffers from limitations such as difficulty in producing and stacking thin plates for first-order QPM.
Synchronously Pumped Optical Parametric Oscillator With Anomalous Wavelength Tuning Behaviour
Authors: Loza-Alvarez P. , Sibbett W. , Kinsler P. , New G. H. C.
Published: February 2020

High repetition rate, synchronously pumped optical parametric oscillators (OPOs) have been widely used to extend the tuning wavelength range that can be accessed by conventional femtosecond and picosecond lasers.1 The oscillation frequency of an OPO can be controlled in several different ways. One technique involves tuning the pump wavelength, while another involves changing the crystal parameters such as the temperature and angle (birefringent phase-matching) or the grating period (quasi-phase matching). In a third method, perhaps the simplest of all, tuning is effected by adjusting the OPO cavity length. In general, this is possible due to the fact that OPO oscillation is achieved under synchronous pump conditions, so that shorter (longer) signal wavelengths will oscillate for shorter (longer) OPO cavities in view of the inherent normal dispersion of the nonlinear crystal. In this paper, we report the characterisation of an OPO that exhibits a distinctive (and anomalous) tuning behaviour when the cavity length tuning procedure is applied.
Femtosecond Energy Concentration in Nanosystems Coherently Controlled by Excitation Phase
Authors: Stockman M. I. , Faleev S. V. , Bergman D. J.
Published: February 2020

We predict that excitation of a nanosystem with a correspondingly phase-modulated femtosecond pulse can cause concentration of the excitation energy at a small part of that nanosystem. The location of the excited site is coherently controlled by the distribution of the phase along that pulse. We discuss unique possibilities of using this in applications, in particular, for nanoscale ultrafast computing and nano-lithography
Generation of sub-10-fs pulses from a mode-locked Cr3+:LiCAF laser
Authors: Wagenblast P. , Morgner U. , Grawert F. , Kärtner F. X. , Scheuer V. , Angelow G. , Lederer M. J.
Published: February 2020

Cr3+:LiCAF is a very promising material for compact femtosecond laser sources because of its low quantum defect, a broadband emission range around 800 nm, and an absorption band in a spectral range where high-brightness laser diodes are available. For applications such as seeding, ultra high resolution optical coherence tomography, or metrology a compact replacement for the Ti:sapphire oscillator would be highly desirable. Although the gain bandwidth of Cr3+:LiCAF supports pulses substantially shorter than 10 fs, the shortest pulse width so far demonstrated from a mode-locked Cr3+:LiCAF -Laser is 19 fs [2]. It has been suggested that higher order dispersion and the strong Raman-effect occurring in Colquiirite crystals [2, 3, 4] which leads to a red shift of the spectrum each pass through the gain medium is limiting short pulse generation.
Improved temporal and spatial resolution in junction-mixing ultrafast scanning tunneling microscopy
Authors: Yarotski Dzmitry , Taylor Antoinette J.
Published: February 2020

The growing field of nanotechnology requires special tools capable of probing ultrafast dynamics of nanostructures on atomic scales. Recently, two possible practical realizations of such technique were proposed, which combine the high spatial resolution of scanning tunneling microscopy (STM) and femtosecond temporal resolution of the nonlinear optical spectroscopy [1,2]. One of them, photoconductively-gated STM is believed to be limited in its spatial resolution to several tens of nanometers due to capacitive coupling between the tip and the sample under study [3]. On the other hand, junction-mixing STM (JM-STM) relies only on the intrinsic nonlinearity of the tunneling junction current-voltage characteristic and should provide the atomic resolution of a conventional STM. In order to confirm this assumption, experiments have been performed, which demonstrated the spatial resolution of JM-STM to be of the order of 1 nm and the temporal resolution to be more than 35 ps (full width at half maximum (FWHM) of the detected transient current pulses) [4]. Unfortunately, this temporal resolution is not yet sufficient for the ultrafast dynamics studies. Here we present recent results for JM-STM with a greatly improved temporal resolution of less than 13 ps FWHM and with a spatial resolution of 1 nm.
Feedback control of photosynthetic light harvesting
Authors: Wohlleben W. , Zeidler D. , Kompa K. L. , Motzkus M. , Herek J. L. , Sundström V.
Published: February 2020

Quantum control of photochemistry exploits molecular interferences by adjusting the phases of multiple quantum pathways to different product channels via adapted excitation light. Experiments implement a learning loop in which molecular feedback iteratively refines the excitation pulse until an optimum solution directs the photoreaction towards a desired channel [1]. So far, feedback control has been absent from the world of biology. Furthermore, only few examples have proven explicitly the role of molecular coherence. Here we report feedback-optimised coherent control of biological function, namely regulation of the energy flow pathways in the 125 kDa light-harvesting antenna complex LH2 from Rhodospeudomonas acidophila, a photosynthetic purple bacterium.
Femtosecond Study of Self-Trapped Vibrational Excitons in Crystalline Acetanilide
Authors: Edler J. , Hamm P.
Published: February 2020

Femtosecond infrared spectroscopy of delocalized NH and amide I excitations of crystalline acetanilide confirms that self-trapping in hydrogen-bonded model peptide crystals stabilizes the excitation. The phonons which mediate self-trapping are identified.
Hybrid chirped pulse amplification
Authors: Jovanovic Igor , Barty Christopher P. J.
Published: February 2020

We present a novel chirped pulse amplification method which combines optical parametric amplification and laser amplification. High efficiency is achieved without the use of electro-optic modulators using a simple tabletop pump laser.
Ultrafast coherent spectroscopy of single quantum dots
Authors: Günther Tobias , Müller Kerstin , Lienau Christoph , Elsaesser Thomas , Eshlaghi Soheyla , Wieck Andreas
Published: February 2020

The nonlinear optical response of single quantum dots is studied with femtosecond resolution. We show that the free-induction decay and coherent Stark effect of the single exciton polarization are strongly perturbed by many-body interactions.
Ultrafast coherent electron transport in quantum cascade structures
Authors: Eickemeyer F. , Reimann K. , Woerner M. , Elsaesser T. , Barbieri S. , Sirtori C. , Strasser G. , Müller T. , Bratschitsch R. , Unterrainer K.
Published: February 2020

The first mid-infrared pump-probe study of an electrically driven quantum cascade structure reveals an oscillatory gain recovery after femtosecond excitation, giving evidence for coherent electron motion from the injector into the active region.
Few-optical-cycle regime for the generation of high-order harmonic: enhanced conversion and brightness
Authors: Villoresi P. , Pascolini M. , Poletto L. , Tondello G. , Nisoli M. , Priori E. , Sansone G. , Stagira S. , De Silvestri S.
Published: February 2020

The interaction of a few-optical-cycle pulse with matter have shown novel phenomena [1]. Moreover, the high intensity which can be realized for a few semi-cycles of the laser optical-period may induce the tunnel ionization or even ionization due to barrier suppression. The resultant photoelectrons are driven in a coherent motion which influences both the above-threshold-ionization electron spectrum as well as the photon spectrum emitted due to recombination. In particular, in this work we analyze the condition of enhanced generation efficiency and brightness of extreme ultraviolet (XUV) radiation in the case of a 7 fs pump pulse on a jet of different gases.
High-order self-dispersion-compensation in a Ti:sapphire laser oscillator
Authors: Crespo H. , Guerreiro A. , Cataluna M. A. , Mendonça J. T.
Published: February 2020

We describe a new regime of operation were sub-10-fs ultrashort laser pulses with symmetric spectra centered at 800 nm can be directly generated from a prism-dispersion-controlled modelocked Ti:sapphire oscillator that only uses commercially available optics.
3/2 Harmonic Generation by Femtosecond Laser Pulses on Solid Targets
Authors: Tarasevitch A. , Dietrich C. , Blome C. , Sokolowski-Tinten K. , von der Linde D.
Published: February 2020

3/2 harmonic is generated by femtosecond pulses in a very steep-gradient plasma on solid surfaces. A well-collimated harmonic emission with high conversion efficiency (5 × 10−4) and an unusually broad spectrum is observed.
Laserfields obtained through optimal control theory throw light on Raman type control experiments
Authors: Hornung T. , Motzkus M. , de Vivie-Riedle R.
Published: February 2020

Optimal control theory is found to be initial guess dependent leading to complex fields. Here we circumvent this problem and provide robust and realizable laser fields for direct comparison with experimental learning loop control results.
Coulomb correlations, spectral line shapes, and size distributions of CdSe colloidal nanocrystals
Authors: Scholes Gregory D. , Hines Margaret A. , Salvador Mayrose
Published: February 2020

We report transient photon echo data for CdSe nanocrystals at 4.4K. The data and simulations, which include the effects of many-particle correlations, suggest that a significant contribution to the signal originates from an instrinsic inhomogeneity in the heavy-hole-type resonance energy. Our results indicate homogeneous line shapes that are consistent with those reported in single molecule studies.
Local structure and dynamics of liquid acetone by heterodyned 2D IR spectroscopy
Authors: Ge Nien-Hui , Hochstrasser Robin M.
Published: February 2020

Multiple pulse two-dimensional IR spectroscopy is a promising approach to obtain ultrafast snapshots of molecular structures in the condensed phase. Here we show that nonlinear IR spectroscopy exposes the dynamics of the local structure of liquids: results for liquid acetone are obtained. The liquid responds like a molecular excitonic system undergoing structure fluctuations. Isotope dilution with acetone-2-13C shifts the C=O frequencies by ~40 cm−1, allowed measurement of the coupling of labeled and unlabeled molecules. Results from new heterodyned 2D transient grating experiments reveal the dynamics of intermolecular energy transfer.
Photo-Isomerization of Small Molecules in Solution: Studies of ICN(aq) and NO3−(aq)
Authors: Madsen Dorte , Larsen Jane , Thøgersen Jan , Keiding Søren R.
Published: February 2020

Photo-isomerization of aqueous nitrate and aqueous iodine cyanide is studied by transient absorption spectroscopy covering the spectral range 194–700 nm. ONOO
−
and INC are formed in 1 ps and < 0.5 ps, respectively.
Ultrashort-pulse-laser ablation of metals: Significant changes in ablation rates with depth
Authors: Lausten Rune , Olesen Jakob A. , Vestentoft Kasper , Balling Peter
Published: February 2020

Femtosecond-laser ablation rates for a broad range of metals have been investigated and general trends are discussed. A newly developed technique allows the accurate measurement of the ablation rates at all times during the formation of holes.
Convenient tunability of sub-10 fs-pulses in the visible range
Authors: Baigar E. , Braun M. , Peine A. , Konjaev V. , Zinth W.
Published: February 2020

We present a system for tunable laser pulses with a duration of about 7 fs. The pulses are generated by compression of the output of a tunable non-collinear optical parametric amplifier (NOPA) via a fiber compressor.
Photonic Crystal Fibers: Speeding up the Ultrafast
Authors: Russell P.St.J. , Ortigosa-Blanch A. , Wadsworth W.J. , Knight J.C.
Published: February 2020

The first working example of photonic crystal fibre (PCF) was reported at the Optical Fiber Communications Conference in 1996 [1]. In place of the usual cylindrically symmetric refractive index profile, peaking in the centre, PCF is formed from a strand of pure silica glass which has running parallel to its axis a carefully designed lattice of microscopic air capillaries [2]. Guiding “cores” are created in this two-dimensional “photonic crystal array” by filling in or enlarging groups of one or more air holes [3-4].
Population dynamics in quantum structures
Authors: Müller T. , Bratschitsch R. , Strasser G. , Unterrainer K.
Published: February 2020

An interband pump/intersubband probe technique is applied to measure the dynamic intersubband absorption spectrum of an undoped GaAs/AlGaAs coupled quantum well excited by an ultrashort interband optical pulse.
Control of Ground State Dynamics in Polymers with Shaped Pulses
Authors: Zeidler D. , Frey S. , Wohlleben W. , Motzkus M. , Busch F. , Chen T. , Kiefer W. , Materny A.
Published: February 2020

Coherent control of the ground state vibrational dynamics via a Raman process is demonstrated in polydiacetylene. The relative amplitudes and phases of the normal modes could be set.
Ultrafast Pump-Probe and Resonance Raman Spectroscopic Study of Excited State Electronic Coupling in Two Related Hexanuclear Charge Transfer Compounds
Authors: Mordas Carolyn J. , Pfennig Brian W. , Bocarsly Andrew B. , Schreiber Elmar
Published: February 2020

Photoinduced multi-electron transfer is reported in two hexanuclear intervalant charge transfer complexes of Pt(IV) and Fe(III). Femtosecond pump-probe spectroscopy, resonance Raman and electrochemical data suggest the degree of excited state electronic coupling is tunable by changing the electronic nature of the bridging ligand.
Vibrational Dynamics, Mode Coupling and Structure of Acetylproline-NH2 Dipeptide
Authors: Rubtsov Igor V. , Hochstrasser Robin M.
Published: February 2020

Vibrational relaxation, mode coupling and peptide structure were investigated by femtosecond two-dimensional infrared spectroscopy of an acetylproline-NH2 model dipeptide. Three high frequency vibrational modes were examined, two amide-I modes (1693 and 1633 cm−1) and an amide-II amine end (denoted as (N-)) mode (1580 cm−1). Efficient vibrational energy transfer between amide-I and amide-II bands located on the same amide has been clearly observed (τ~2.8 ps). The change in the nature of the cross peaks from off-diagonal to diagonal coupling types, caused by vibrational energy transfer (EnT), has been analyzed for the first time. The energy transfer process from the amide-I band acetyl end (C-) to the amide-II band has been also detected (~10 ps). No clear EnT between two amide-I bands was seen, giving an estimate of the upper limit of 20 ps for the EnT. An evolution of the diagonal spectrum was clearly demonstrated, giving a reason for the nonexponential decay kinetics observed in conventional pump-probe experiments. A long lived cross-peak was detected in each of the amide-I bands when the other amide-I band was excited, indicating the existence of at least one vibration in the molecule which remains excited for much longer than the average lifetime of the three vibrations being studied. Its decay time (~10 ps) represents the vibrational cooling of the dipeptide by energy transfer to the solvent. The coupling strength between the three vibrational modes was determined. The angles between the transition dipoles of these modes given by the polarization measurements were close to those of a C7 conformation.
Preparation of oriented molecules for ultrafast spectroscopic studies
Authors: Sakai Hirofumi , Minemoto Shinichirou , Nanjo Hiroshi , Tanji Haruka , Suzuki Takayuki
Published: February 2020

The manipulation of atoms and molecules is one of the most important and intriguing subjects in modern physics, chemistry, and biology. The control of the spatial orientation of molecules is especially important for studies of orientational effects in chemical reactions [1]. The alignment of neutral molecules by a strong linearly polarized laser field has already been demonstrated [2,3]. At present, electric hexapole focusing and strong static electric field orientation are employed to control the orientation of polar molecules. However, electric hexapole focusing works only for symmetric top molecules and strong static electric field orientation is effective only for certain molecules possessing large permanent dipole moments. The realization of molecular orientation to arrange any polar molecules in a “head-versus-tail” order is a next challenging subject.