bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature-Dependence of the Ultrafast Intermolecular Dynamics of Amides: Formamide, N-Methylformamide, N,N-Dimethylformamide, N-Methylacetamide, and N-Methylpropionamide from 290-370 K‡
Authors: Castner Edward W. , Chang Yong Joon
Published: February 2023

Using the femtosecond optical-heterodyne detected, Raman-induced Kerr effect spectroscopic technique1,2 (fs-OHD-RIKES), we have characterized the full spectrum of the intermolecular vibrational and diffusive dynamics for a series of five amides. The OHD-RIKES birefringence transients of the neat liquids formamide (FA), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N-methylacetamide (NMA), and N-methyl-propionamide (NMP) were measured in at temperatures in the range 290-370 K. Because we have used 50 fs, transform-limited pulses to perform the experiments, we impulsively excite all of the intermolecular motions in the 0 to 400 cm-1 range. Use of optical-heterodyne detection permits observation of a response linear in the molecular response; thus we can analyze the data in both the time and frequency domains by Fourier-transform inversion.2
Ultrafast Photophysics of Conjugated Polymers, Blends, and Devices
Authors: Schwartz Benjamin J. , Hide Fumitomo , Andersson Mats R. , Heeger Alan J.
Published: February 2023

The photophysics of conducting polymers are of interest both for the fundamental information they provide about the nature of excitations in low-dimensional systems, and for the enormous practical potential they offer in the production of low cost, readily processible electroluminescent devices.[1-5] The technological goals in constructing organic LED's include improvement of the quantum efficiency of the luminescence and control over the emission frequency. By constructing new polymers with different side groups and doping polymer films with other luminescent molecules, both of these goals can be met. In this paper, we present ultrafast photophysical studies of a novel conjugated polymer with a high luminescence efficiency. Comparison of the transient absorption and emission dynamics of the new polymer, an alkyl-substituted poly(p-phenylenevinylene) (a-PPV), to unsubstituted or alkoxy-substituted PPV's [1-4] demonstrates that non-radiative pathways which compete with luminescent channels are significantly curtailed in the new material. Additional femtosecond studies on a-PPV/dye molecule blends show that rapid energy transfer takes place, opening the possibility for tuning the emission by the choice of dye molecule. Light emitting diodes constructed from the new polymer and the polymer/dye blends demonstrate improvement of the electroluminescence efficiency upon doping, verifying that energy transfer competes effectively with non-radiative channels under in-situ conditions.
Factoring the Contribution of Through-Space and Through-Bond Interactions to Rates of Photoinduced Electron Transfer in Donor-Spacer-Acceptor Molecules using Ultrafast Transient Absorption Spectroscopy
Authors: Gosztola David , Wang Bing , Wasielewski Michael R.
Published: February 2023

It is well known that the rate of intramolecular electron transfer in linked donor-acceptor molecules is not only dependent upon the distance and orientation between the donor (D) and acceptor (A), but is also dependent upon the electronic properties of the intervening spacer (S) molecules between the redox centers[1]. If the distance between D and A is small enough to allow for direct overlap between the frontier orbitals of the donor and acceptor, electron transfer may occur by means of a through-space mechanism. When the D and A centers are too far apart for direct orbital overlap to be important, electron transfer may occur via a superexchange or through bond interaction. Both contributions to the total electronic coupling matrix element for electron transfer between the donor and acceptor depend on the distance and the orientation of the various molecular components. Thus, it is important to hold both the distance and geometry of the donor and acceptor fixed as the properties of the covalent spacer between them are varied. Achieving this degree of structural control in a D-S-A molecule is often a difficult task.
Formation of diphenylacetylene following the photodissociation of diphenylcyclopropenone in solution
Authors: Hirata Yoshinori , Nishiyama Katsura , Asano Yasuaki , Okada Tadashi
Published: February 2023

Irradiating diphenylcyclopropenone (DPCP) with a UV light, diphenylacetylene (DPAC) is produced by decarbonylation reaction with a quantum yield of unity. Previously we reported that DPAC in the excited singlet states is formed immediately after the picosecond laser pulse excitation shorter than 320 nm.1 In this paper we present the results of the transient absorption measurements of DPCP in c-hexane with a higher time resolution. Transient absorption band which can be assigned to the excited state of DPCP was observed around 470 nm.
3-D Optical Storage and Engraving Inside Transparent Materials†
Authors: Glezer E.N. , Milosavljevic M. , Huang L. , Finlay R.J. , Her T.-H. , Callan J.P. , Mazur E.
Published: February 2023

Three-dimensional optical data storage offers the potential for very large recording capacity and has the possibility of parallel read-out. In addition to research in volume holographic data storage, work has been done in point-like binary 3-D optical storage. Optical recording at a density of 1.6×1012 bits/cm3 has been demonstrated in a photopolymer using two-photon absorption [1]. The stored information consisted of less than 1% changes in the local index of refraction, and was read out serially with a differential interference contrast (DIC) laser microscope.
Broadband Surface Second Harmonic Generation from Si/SiO2 Interfaces
Authors: Cundiff S.T. , Knox W.H , Baumann F.H. , Roy P.K. , van Driel H.M.
Published: February 2023

Surface second harmonic generation (SSHG) from the Si-SiO2 interface is of considerable interest because it is sensitive to surface steps [1], straining of subsurface bonds [2] and surface roughness [3], all of which are important in the fabrication of integrated circuits. By using 10 fs pulses we are able to obtain acceptable signal to noise ratio using less than 30 mW, as compared to the hundreds of mW necessary for 100 fsec pulses [1,3]. The p-polarized pulses (45° incident angle) are generated by a Kerr-lens-modelocked Ti: sapphire laser [4]. Additionally the very broadband nature of these pulses allows us to observe resonance behavior in the SSHG by simply spectrally resolving the SSHG, i.e., tuning the laser is not required.
Broadband Fiber Dispersion Compensation for Sub-100-femtosecond Pulses with Compression Ratio of 300
Authors: Chang C.-C. , Weiner A. M.
Published: February 2023

Dispersion compensation techniques aimed to upgrade 1.3 µm single mode fibers (SMF) for use in 1.5 µm optical communication systems are of great current interest. Several groups have utilized dispersion compensating fiber with large normal dispersion at 1550 nm to equalize the anomalous dispersion in SMF for lightwave system experiments [1, 2]. In our research we are applying these techniques to achieve dispersion equalization for femtosecond pulse transmission, for which not only the dispersion but also the dispersion slope must be compensated [3]. By using a special dispersion compensating fiber (DCF) with favorable dispersion characteristics [4], we demonstrate nearly dispersion-free propagation of ~60-fsec pulses over >40 m of fibers. Our experiments demonstrate an all-fiber dispersion compensation systems capable of 300-fold pulse recompression for sub-100-femtosecond pulses. Compared to other femtosecond fiber dispersion compensation experiments [5], we achieve nearly a factor of five higher compression ratio with approximately seven times shorter pulses. Furthermore, we apply spectral interferometry [6] to perform measurements of the dispersion properties of our concatenated fiber link.
Picosecond time-resolved pump-probe XUV absorption L-edge spectroscopy
Authors: Nantel M. , Workman J. , Maksimchuk A. , Umstadter D.
Published: February 2023

We present what we believe to be the first measurements of broadband XUV absorption spectroscopy with picosecond time scale resolution. A 10-Hz, 60 mJ 100-fs laser system is used to create a quasi-continuum of XUV radiation (30 Å < λ < 300 Å) from a gold plasmas to act as a probe source. The temporal duration of the probe is typically on the order of 20 ps but can be made shorter or longer by varying the laser parameters.1 Part of the 100-fs laser beam also provides a delta-function pump beam to heat a sample onto which the XUV probe source is focused by a novel XUV imaging optics. Time-resolved results are gathered by two different methods: 1) a variable delay between the pump laser and the probe XUV source is used to collect spatially-resolved spectra of the sample's absorption at different times during the laser heating and 2) a unique jitter-free x-ray streak camera2 developed at the Center for Ultrafast Optical Science is used to obtain temporally-resolved absorption spectra. This broadband time-resolved absorption spectroscopy technique offers a very interesting and flexible alternative to synchrotrons for experiments such as time-resolved EXAFS, chemical dynamics and ion characterization in laser ablation plumes.
Ultrafast Coherent Spin Torques in Magnetic Quantum Wells
Authors: Baumberg J. J. , Crooker S. A. , Flack F. , Samarth N. , Awschalom D. D.
Published: February 2023

Introducing magnetic material into semiconductor nanostructures evokes potent magnetic tuning of the spin-split energy levels due to the strong exchange coupling between the quantum-confined charge carriers and the sublattice of magnetic ions. By uniting low-dimensional magnetic heterostructures with ultrafast spin spectroscopy we discover a new aspect to these systems, the exchange-coupled spin torques acting on both photoinjected carriers and the embedded local moments. Our time-resolved Faraday rotation technique1 identifies the initial injection of spin-polarized carriers, multi-terahertz precession of the electrons, and the coherent transfer of hole angular momentum to the magnetic subsystem via the ultrafast rotation of the local moments. The perturbed ions then undergo free-induction decay, thus enabling the first time-domain all-optical electron spin resonance (ESR) measurements in submonolayer magnetic planes.
Spectrally-resolved, DC-balanced homodyne detection for ultrafast, multimode quantum field state measurement
Authors: Walmsley Ian A. , Iaconis Chris
Published: February 2023

Ultimately the properties of all optical fields are contained in the density matrix that specifies their quantum mechanical state. It has only recently been demonstrated that it is possible to actually reconstruct this density matrix from measured data, and to do so with temporal resolution of a few hundred femtoseconds.[1] This technique, known as Optical Homodyne Tomography (OHT), is unfortunately restricted to the measurement of only single mode radiation. In fact it selects out from the test field only those components which overlap temporally with the local oscillator pulse mode.
High Energy 10 fs Pulses by a New Pulse Compression Technique Using Hollow Quartz Waveguide
Authors: Nisoli M. , De Silvestri S. , Svelto O.
Published: February 2023

A well established method for the generation of ultrashort pulses is optical pulse compression, which consists in spectral broadening by self-phase modulation in a single-mode optical fiber followed by chirp compensation into suitable phase dispersive elements. In this way pulses as short as 6 fs have been obtained [1]. The use of single-mode fibers is limited to low energy (nanojoule) pulses due to both material damage and appearance of high-order nonlinearities. So far spectral broadening of high energy femtosecond pulses was achieved in bulk materials [2] where the non-uniform transverse intensity profile of the beam represents a limitation. A compression technique for high energy ultrashort pulses must have a large diameter single mode guiding element with sufficiently high damage threshold and very fast third order non-linear optical susceptibility.
Atomic Streak Camera Probing of Wave Packet Decay: plus a FIR streak camera concept
Authors: Lankhuijzen G. M. , Noordam L. D.
Published: February 2023

An atomic Rydberg electron wave packet above the saddle point of the combined Coulomb and static electric field potential [1], created by a short laser pulse, shows a few oscillations in angular momentum (l) and radial co-ordinate before escaping from the atomic potential [2]. Up to now, experimental studies on the dynamics of the wave packet focused on recurrences of wave packets to the atomic core. These studies have been carried out both in the (1) time and (2) frequency domain. (1) In optical pump-probe studies the overlap near the atomic core of the evolved wave packet with the initial wave packet is directly measured as a function of time. (2) These recurrences of the launched wave packet to the atomic core lead to resonant structure in the photoionization spectrum. We introduce a new device, the atomic streak camera, which measures directly the escape over the saddle point of the Rydberg electron in a static electric field. By measuring the time dependent leaking of the wave packet over the saddle point, instead of measuring recurrences to the atomic core we found that the life time of the Rydberg electron as measured by an optical technique is not the same as the time it takes the electron to leave the atom. Optical techniques measure how many recurrences to the core region the electron makes, and have no access to other parts of the atomic potential. Hence, while the electron might no longer be visible for optical techniques it can still be in the atomic potential, and ionization is not yet seen by the atomic streak camera.
Femtosecond Chemistry
Authors: Zewail Ahmed
Published: February 2023

Summary not available.
Time Resolved Electron Transfer Studies Between Metallointercalators in DNA
Authors: Hormann A. , Olson E. J. C. , Barbara P. F. , Arkin M. R. , Stemp E. D. A. , Holmlin R. E. , Barton J. K.
Published: February 2023

This paper reports the first ultrafast studies on the rates of DNA-mediated forward and reverse electron transfer between photoexcited [M(phen)2dppz]2+ (M=Ru or Os, phen =1,10-phenanthroline, dppz = dipyrido[3,2:a-2′,3′:c]-phenazine) and various electron acceptors in order to ultimately determine the distance dependence of electron transfer kinetics with DNA as an environment.1,2 Previously Barton, Turro, and coworkers have presented evidence that electron transfer in DNA can occur rapidly over an extraordinarily large distance3 with a more shallow distance dependence than that for other media, such as liquids and proteins.4,5 Some theoretical work supports the shallow distance dependence which is attributed to a long range, thermally activated coherent mechanism involving virtual excitation of the DNA "bridge".6 Utilizing time-correlated single photon counting (TCSPC), we observe a substantial fraction of photoexcited [M(phen)2dppz]2+ (M=Ru, Os) exhibits fast oxidative quenching (kq > 3 x 1010 s−1) in the presence of intercalating Rh(III) acceptors while the remaining excited-state species exhibit a range of quenching constants less than 108 s_1. Transient-absorption experiments on the picosecond timescale indicate that, for a series of donors bound to mixed sequence DNA, the majority of back electron transfer is also very fast (ca. 1010 s−1). Importantly, the rate constant for the fast ground-state recovery is independent of loading of Rh(III) intercalators on DNA. As shown in Figure 1, regardless of whether the average loading of metal complexes is 1 in 33 basepairs or 1 in 10 basepairs, the fast bleach recovery exhibited by [Ru(phen)2dppz]2+ is well fit under all conditions by an exponential decay of 9 x 109s−1. Separate ultrafast data suggests that, like the recombination reaction, the fast quenching *M2+ is simple first-order at early time. If the early time electron transfer kinetics were not simple first order, and the electron transfer rate decayed with an exponential distance dependence (i.e. ≅ a factor of 30 per base step [3.4 Å]), our TCSPC apparatus should be able to observe some evidence of the slower components with rate constants in the range of 1010 - 108 s−1. The absence of rates in this range is evidence that the electron transfer is simple first order at time < 10 ns. This result has implications with regards to the donor-acceptor separations on DNA. Throughout most of the titration, intercalators are dilute on the double helix and statistics show that the amount of fast quenching and ground-state recovery observed is too great to be accounted for by random loading of nearest-neighbor pairs. Thus, either the electron transfer reaction must involve clustering of the donor and acceptor on the helix or the DNA-mediated interaction must occur over long distance.
Chemical Reaction Observed by Ultrafast X-ray Absorption
Authors: Jiang Zhiming , Ikhlef Abdelaziz , Kieffer Jean-Claude , Ráksi Ferenc , Wilson Kent R.
Published: February 2023

X-ray absorption, in the form of chemical shifts and EXAFS measurements can interrogate selected elements to reveal their ionization states as well as the distances to nearby atoms, in principle on the ultrafast time scale. Shape resonances, which we have studied in the present experiment, are high amplitude absorption resonances in the near edge spectral region close to the absorption threshold for a particular shell, and occur in symmetrical molecules. The SF6 molecule exhibits intense shape resonance lines at the sulfur K and L edges, due to multiple scattering and interference of the photoelectrons by the fluorine atoms symmetrically surrounding the central sulfur atom. As the molecule dissociates, losing F atoms and its high symmetry, the resonance should greatly diminish or disappear.
Ultrafast Dynamics in Intermolecular Electron Transfer
Authors: Yoshihara Keitaro , Pal Haridas , Shirota Hideaki , Nagasawa Yutaka , Tominaga Keisuke
Published: February 2023

Electron Transfer (ET) is one of the most common reactions in chemistry and biology. For the past decade critical comparison between theory1,2 and experiments3-6 has been giving important insight into the dynamical aspects of ET in solution. Contemporary ET theories which are based only upon the solvent polarization relaxation have predicted that the ET reactions are controlled by the solvent fluctuations and the maximum ET rate for a barriers reaction cannot exceed the solvation rates. The dependence of the ET rate constants on the solvation times has experimentally been demonstrated by many authors.
Hot Electron Reaction Dynamics at GaAs(100) Surface Quantum Wells
Authors: Miller C. C. , Diol S. , Schmuttenmaer C. A. , Cao J. , Mantell D. A. , Gao Y. , Miller R. J. D.
Published: February 2023

Surface mediated electron transfer is the most ubiquitous of all surface reaction types and forms the basis of electrochemistry and many imaging technologies (photography, xerography). This process also holds great promise as a simple system for efficient solar energy conversion. Providing interfacial charge transfer processes can be made to occur competitively with thermalization dynamics, it should be possible to store energy as chemical potential at hybrid semiconductor/molecular junctions and avoid heat losses in conventional solid state solar cells (and thereby double theoretical efficiency limits). This specific mechanism is referred to as the hot electron model for semiconductor photochemistry [1] (Fig.1) and requires that the electron transfer occur in the strong coupling or adiabatic regime. The degree of electronic coupling between a discrete molecular state adsorbed to the surface and the highly delocalized band states of the single crystal is the key fundamental issue. In addition, the dynamics of interfacial charge transfer have to be quantified relative to the electron thermalization dynamics of field accelerated electrons (≤ 1 eV above the CBM) which are the dominant source of photoinduced hot electrons at semiconductor liquid junctions.
Ultrabroad-band ring oscillator for short pulse generation
Authors: Xu L. , Spielmann Ch. , Krausz F. , Szipöcs R.
Published: February 2023

Approaching the gain-bandwidth-limit in Kerr-lens-mode-locked (KLM)1 Ti:sapphire (Ti:S) and related vibronic solid state lasers has been primarily limited by the finite high-reflectivity bandwidth Δν
HR
of quarterwave multilayer dielectric mirrors and the finite constant-group-delay-dispersion bandwidth Δν
GDD
of prism pairs. Although the discovery of chirped multilayer dielectric mirrors2 and their subsequent use in KLM Ti:S lasers3 improved the situation, several problems have remained to be solved: i) a quarterwave dichroic mirror used for pump beam coupling and a quarterwave output coupler were employed and hence limited Δν
HR
also in mirror-dispersion-controlled systems,3 ii) initiating mode locking becomes more and more difficult for shorter pulse durations. This latter problem relates on the one hand to the low negative GDD required for sub-10fs pulses. On the other hand, self amplitude modulation can not be maximized as suggested before4 due to saturation problems at very short steady-state pulse durations.
Advances in all-solid-state ultrafast lasers
Authors: Keller U.
Published: February 2023

An ideal saturable absorber for passively pulsed laser systems has instantaneous response time, is perfectly broadband, has no residual loss, and has a variable saturation fluence. Kerr-lens modelocking (KLM) is an artificial saturable absorber with some of these ideal properties. Semiconductor saturable absorber also offer a distinct range of saturable absorber parameters not available with other approaches. We use semiconductor materials in a monolithic antiresonant Fabry-Perot structure to achieve many of the desired properties. One result of these devices has been the demonstration of "real-world" modelocked solid-state lasers with pulse widths to below 100 femtoseconds. By "real world", we mean diode-pumped, self-starting lasers requiring no critical cavity alignment.
Ultrafast Visible Optical Parametric Oscillators: A Route to Tunable Sub-10-femtosecond Pulses?
Authors: Gale G. M. , Cavallari M. , Hache F.
Published: February 2023

Titanium:sapphire pumped optical parametric oscillators (OPO) now allow reliable generation of tunable femtosecond pulses, either directly in the visible [1,2], or in the near-infrared spectral region. Typical IR. OPO pulse-widths lie in the 40 to 100 fs range, comparable to the high-power Ti: sapphire pump-pulse duration employed in these experiments. However, the potentially very wide bandwidth of the parametric process, which is not limited by optical transition breadths, allows one to envisage the production of OPO pulses much shorter than the pump pulse.
Photocarrier Relaxation in the Quantum Kinetics Regime
Authors: Bar-Ad S. , Kner P. , El Sayed K. , Chemla D.S.
Published: February 2023

The thermalization of nonequilibrium carrier distributions involve fundamentals of thermodynamics and solid states physics. Femtosecond spectroscopy has been employed to study this process,[1] and was analysed in the framework of Bolzmann Kinetics. [2] However, during and shortly after an ultrashort laser excitation, carrier kinetics are drastically altered. At this early stage the Coulomb potential is still unscreened and there is essentially no energy conservation in two-particle scattering events, instead scattering becomes non-local in time. In this regime the evolution of momentum-dependent occupation numbers can only be described by Quantum Kinetics, including memory structure in the scattering integrals.[3]
Coherent Excitation of Magnetoexciton Wavepackets
Authors: Cundiff S.T. , Koch M. , Knox W. H. , Shah J. , Stolz W.
Published: February 2023

The optical properties of magnetoexcitons (ME) have been of a topic of considerable interest, in particular, there have recently been several studies of the transient response using ultrashort pulses [1,2]. We present the results of experiments in which multiple ME states are coherently excited using a 40 fs pulse, creating a ME-wavepacket. These represents the first such observations as previous studies were either for incoherent excitation [1] or excited only a single ME state [2].
Magnetic field dependence of exciton spin dynamics in GaAs quantum wells
Authors: Grevatt T. , Traynor N.J. , Worsley R.E. , Harley R.T.
Published: February 2023

We discuss the significance of spin-relaxation for exciton dephasing in quantum well systems at low temperatures and also study the magnetic field dependence of spin-relaxation. We have used a novel technique employing reflective probing of pump-induced transient linear birefringence to investigate ultrafast dephasing of n=1 heavy-hole excitons as a function of magnetic field in GaAs/AlGaAs samples. We have also measured the spin-relaxation time and exciton lifetime of the samples. Exciton spin-relaxation in such samples is dominated, in zero field, by simultaneous electron and hole spin flips driven by confinement-enhanced exchange interaction [1]. We find that for localised excitons in narrow wells pure dephasing processes are negligible and spin-relaxation is dominant in zero magnetic field. In applied field the exciton spin-relaxation is strongly suppressed and the dephasing becomes lifetime-limited.
Sub-picosecond intermediates in energy transfer and electron transfer in reaction centers of purple bacteria
Authors: Vos Marten H. , Jones Michael R. , Breton Jacques , Lambry Jean-Christophe , Martin Jean-Louis
Published: February 2023

Using femtosecond near-IR absorption spectroscopy with tunable pulses of 30 fs we have investigated the controversial issues of the pathways and time scales of the processes of energy transfer from the accessory bacteriochlorphylls B and the bacteriopheophytins H to the primary donor P and of electron transfer from P* to HL. Using a compressed continuum for probing the transient spectra allows to monitor the evolution of the donor and acceptor states in the same experiment.
Depolarization Study of Energy Transfer in the Photosynthetic Reaction Center
Authors: Jonas David M. , Lang Matthew J. , Nagasawa Yutaka , Fleming Graham R.
Published: February 2023

Electronic energy transfer between the six pigments involved in primary electron transfer in bacterial photo synthetic reaction centers is known to occur in less than 100 fs.(1, 2) In the RC, two bacteriochlorophylls in the special pair (P); two accessory bacteriochlorophylls (B); and two bacteriopheophytins (H) are anchored to a protein scaffold along two branches (which meet at the special pair) with an overall approximate C
2
symmetry. Along each branch, B lies between P and H and is essentially in van der Waals contact with both. The extent of the electronic coupling between the pigments has been controversial.(3, 4, 5, 6) A careful investigation of energy transfer may shed light on the coupling between pigments in the reaction center.
Transient Absorption Studies of the Primary Charge Separation in Reaction Centers of Photosystem II
Authors: Donovan Brent , Walker Larry A. , Yocum Charles F. , Sension Roseanne J.
Published: February 2023

Recent femtosecond and picosecond measurements of the primary charge separation event in photosystem II have resulted in a controversy with regard to the time constant for the primary charge separation process. Klug and coworkers have published a series of papers in support of a ca. 20 ps effective time constant for the appearance of the charge-separated state [1]. Their conclusions are supported by the experiments of McCauley et al. [2] and Freiberg et al. [3]. On the other hand, several groups have published data interpreted as supporting a ca. 3 ps time constant for the primary charge separation [4-6]. In light of this disagreement we have performed a series of subpicosecond transient absorption measurements on the reaction center of PSII. These studies have concentrated on the effect of pump intensity, pump wavelength, and method of sample preparation.
A Widely Wavelength Tunable Mode-locked Fiber Laser using All Fiber Optic Frequency Shifter
Authors: Jeon Min-Yong , Koh Yeon Wan , Yun Seok Hyun , Kim Byoung Yoon , Lee Hak Kyu , Kim Kyong Hon , Lee El-Hang
Published: February 2023

Ultra short pulse generation using a fiber source is a challenging area for all optical communication applications. Many efforts have been devoted into generating short pulses with a variety of methods[1][2]. The wavelength tuning capability of the fiber source are also of a great interest for WDM system application. The sliding frequency soliton fiber laser was reported for a possibility of wavelength tuning within a limited wavelength range[3][4]. In this paper, we report on a successful demonstration of a newly designed all fiber sliding frequency mode-locked fiber laser with a wide tuning range and a sub-picosecond pulse width.
Ultraviolet picosecond pulses from an all-solid-state Ce:fluoride master oscillator and power amplifier system
Authors: Sarukura Nobuhiko , Liu Zhenlin , Izumida Shinji , Segawa Yusaburo , Dubinskii Mark A. , Semashko Vadim V. , Naumov Alexander K. , Korableva Stella L. , Abdulsabirov Ravil Yu.
Published: February 2023

Ultrashort-pulse generation and amplification in the ultraviolet (UV) region has been receiving a great deal of interest for applications. All known UV short-pulse master oscillator and power amplifier (MOPA) systems consist of mode-locked oscillator stages, and excimer power amplifier stages. 1 The above systems are complicated and bulky. However, solid-state tunable UV-laser materials such as Ce3+ ion activated LuLiF4 (LLF) 2 LiCaAlF6 (LiCAF), and LiSrAlF6 (LiSAF) 3,4 have recently been developed. With their broad gain-width, they are attractive for ultrashort pulse applications. To prove that, we have demonstrated UV picosecond-pulse amplification using Ce:LLF. 5 Furthermore, by employing a newly proposed self-injection-seeding scheme, we have directly generated UV picosecond pulse-trains from a Ce:LLF laser 6 and a Ce:LiCAF laser.7 This presentation reports UV picosecond pulse generation and amplification in a compact, all-solid-state MOPA system.
Temperature Dependent Sub-ps Transient Spectroscopy of the Photosystem II Reaction Center
Authors: Groot Marie-Louise , van Mourik Frank , van Stokkum Ivo H. M. , van Grondelle Rienk
Published: February 2023

Time resolved studies of several groups on the reaction center of Photosystem II have revealed the presence of various kinetic and spectral components with lifetimes in the range of sub-ps to ns. While the longer lifetimes are generally ascribed to recombination of the long-lived radical pair P680+Pheo- formed upon charge separation, the origin of the different sub-ps to ps components is controversial and processes as energy transfer, charge separation and exciton relaxation have been proposed. At room temperature e.g., charge separation has been reported to occur in 3 ps [1,2,3,4,5], but Klug and co-workers [6 and references therein] have found that radical pair formation occurs primarily (for ~70%) with a 21 ps time constant.
Polarised pump probe spectroscopy on the light harvesting complex of Rps. viridis at room temperature
Authors: Monshouwer R. , Baltuska A. , van Grondelle R.
Published: February 2023

The purple bacterium Rps. viridis is a Bchl-b containing species that contains only one type of antenna, the LH-1 complex. Electron crystallography has revealed that the photosynthetic membrane of this bacterium contains a highly ordered array of core complexes each consisting of a reaction centre surrounded by a ring of Bchl-b binding antenna subunints [1]. For Bchl-a containing photosynthetic membranes it has been shown using sub-picosecond spectroscopy that both transfer between different antenna complexes and very fast transfer between the pigments of the same complex occurs. This transfer is expressed as a shift of the observed bleaching spectrum [2,3] and depolarisation of the spontaneous emission signal due to transfer between differently oriented pigments [4]. Although there are large homologies between the Bcl-a containing bacteria and Rps. viridis the spectral properties of their LH-1 complexes are rather different [5]. At least at low temperature the LH-1 antenna of Rps. viridis is heterogeneous. These deviating spectral properties make this antenna system interesting to study with sub-picosecond spectroscopy. The timeresolved experiments presented were performed with an amplified Ti:sapphire laser system driving an optical parametric amplifier (OPA). The regenerative amplifier (REGA) produces 4 to 5 μJ pulses of about 180 fs FWHM with a repetition rate of 200 kHz. 25% of the output is used to generate white light in a thin sapphire slab. After selecting the proper wavelength range with bandpass filters, part of the continuum is used as a probe pulse. The remaining 75% of the REGA output is doubled and pumps a two pass OPA that is seeded with the remaining white light continuum. For our experiments the idler frequency was selected from the output of the OPA and used to excite the sample. The detection wavelength was selected with a monochromator behind the sample (bandwidth 5 nm). The cross correlation of the pump and probe pulse was about 100 fs. Membrane fragments were prepared as described before [5].
Wavepacket Motion observed in an Ultrafast Electron Transfer System
Authors: Zinth W. , Engleitner S. , Seel M.
Published: February 2023

Recently it had been shown that ultrafast electron transfer (ET) reactions can occur even faster than relevant reorganisation and relaxation processes /1-3/. These experiments raised a number of new questions such as: How can those ultrafast reactions proceed, what reaction mechanism applies and what is the role of specific vibrational modes or wavepacket motions? In this paper we present new experimental results taken over a wide range of probing wavelengths with highest time resolution on a fast ET-system. We will focus on the system oxazine 1 in two solvents: The first combination is oxazine 1 (OX1) in dimethylaniline (DMA) where an ultrafast light induced ET occurs from DMA to OX1. As a reference system without electron transfer, we use the solvent 1-chloronaphtalene (1-CN) which has similar solvent properties ( dipole moment, dielectric constant, viscosity) as dimethylaniline. The experiments are performed with a CPM-laser based amplifier/compressor system /4/ with red (630 nm) excitation and different probing wavelengths covering the whole visible spectrum. Cross-correlation widths are ≈12 fs in the red and near IR and ≤ 22 fs in the blue-green part of the spectrum.
Femtosecond Optical Spectroscopy and Scanning Probe Microscopy
Authors: Feldstein Mark J. , Wang Weining , Scherer Norbert F.
Published: February 2023

Understanding surface mediated reactions involves the correlation of local electronic and topological structure with reactivity. Further, an improved understanding of localized reactivity would benefit from dynamical studies.1 The study of complex interfaces and mechanisms of electrochemical reactivity would certainly benefit from such insights. Towards this end, a new experimental technique that is a promising approach for simultaneous spatial and temporal resolution of optically initiated dynamics at interfaces is presented. The method, based on the integration of femtosecond-optical spectroscopy and scanning probe microscopy (FOS-SPM), is capable of spatial localization of optically induced phenomenon at interfaces. Spatially localized, time resolved spectroscopic measurements are achieved via coupling of the metal SPM tip to an optical field at the interface.2,3 FOS-SPM has been shown to be capable of identifying and differentiating between different opto-electronic mechanisms, specifically multi-photon ionization (MPI) and optical rectification.4 Preliminary results on the application of FOS-SPM to study localized surface reactivity are presented.
Femtosecond melting rates of crystalline and amorphous Column IV elements
Authors: Ahn H. , Grimes M. K. , Hu X. F. , Downer M. C.
Published: February 2023

Several fs time-resolved reflectivity and second harmonic studies [1] have demonstrated qualitatively that highly photoexcited crystalline semiconductors lose long-range crystalline order (’’melt”) and approach equilibrium liquid optical properties before the material becomes vibrationally excited. A quantitative tight-binding theory of lattice instability driven electronically by dense e-h plasmas, which predicts the material- and carrier density-dependence of the melting time τ
m
, has now been formulated [2], but has not been quantitatively tested. This theory predicts, among other things, that τ
m
scales as
d02M1/2f(N
e
h
), where M = atomic mass, d0 = lattice spacing, and f(N
eh
) is a nearly material-independent function of electron-hole pair density. Since d0 and f(N
eh
) depend only on local (e.g. tetrahedral) bonding structure, crystalline and amorphous Column IV targets of the same material should melt on the same time scale for a given peak density. The measurements presented here with systematically varied target material (C, Si, Ge), target structure (crystalline vs. amorphous), and excitation fluence F confirm the
d02M1/2f(N
e
h
) scaling law quite well for Column IV crystalline targets. However, they reveal that amorphous targets melt more slowly than crystalline targets for a given F, suggesting that peak carrier density is clamped by an ultrafast recombination mechanism unique to the amorphous state [3].
16 fs Pulse Generation and Measurement in the Ultraviolet and Vacuum Ultraviolet
Authors: Backus S. , Peatross J. , Zeek E. , Read K. , Murnane M.M. , Kapteyn H.C.
Published: February 2023

In this paper, we present new experimental results on the generation of ultrafast third (266nm), fifth (160nm), and seventh (114nm) harmonic light in gases. Useful conversion efficiencies are observed, and the efficiency can be optimized by adjusting the chirp of the input pulse. In addition, the pulse duration of the third harmonic is measured at under 16fs, using the technique of self-diffraction frequency resolved optical gating.
Femtosecond time-resolved phase spectroscopy using a novel Sagnac interferometer
Authors: Kobayashi Takayoshi , Misawa Kazuhiko , Kanou Hideaki , Dushkina Natalia , Ueki Akikatsu
Published: February 2023

Femtosecond phase and transmission spectroscopy is important for studies of ultrafast phenomena in dispersive and absorptive materials.1, 2 In the present paper, we demonstrate single-shot measurement of difference phase spectra (DPS) and difference transmission spectra (DTS) using a novel femtosecond Sagnac interferometer.
Generation of 40 fs, 20 TW pulses at 10 Hz
Authors: Antonetti A. , Chambaret J.P. , Cheriaux G. , Curley P.F. , Darpentigny G. , Le Blanc C. , Salin F.
Published: February 2023

The application of the chirped pulse amplification technique to Ti:sapphire has made possible the generation of energetic sub-100 fs pulses. Sub- 20 fs Ti:Sapphire oscillators are now available, and amplification of pulses shorter than 40 fs has been demonstrated [1,2]. Although these pulses have very high peak power they can be useful to high field physics and specially to solid-state target experiments, only if they are free of any prepulse or wing. We describe here a Ti:sapphire amplifier which has been designed to produce pedestal free, 20TW,40fs pulses at 10 Hz. In order to minimize prepulses, we designed the amplifier with a broad transmission bandwidth, minimum material path length, high gain, and introduced an aberration free system for stretching and recompressing the pulses [3].
Multi-photon Molecular Excitation to Illuminate Non-linear Laser Microscopy
Authors: Webb Watt W. , Xu Chris
Published: February 2023

Molecular excitation by two or more infra red photons simultaneously absorbed from strongly focused 100 femtosecond mode locked laser pulses provides intrinsic 3-d resolution for fluorescence microscopy and photochemical micro pharmacology in living biological cells. Confinement of non-linear excitation to the focal volume illuminated by ~1016 photons/nm2s eliminates out of focus photobleaching and photodamage and provides intrinsic 3-d resolution. To facilitate this technology new methods have developed for accurate measurements of multi-photon excitation cross sections and spectra in the absence of adequate data to guide non-linear laser microscopy applications. Absolute cross section measurements have been facilitated by development of a method that takes advantage of the interference of excitation pulse trains that are time shifted by a conventional Michaelson interferometer to allow variable relative delay of two spatially superimposed beams. Two photon excitation with single mode CW lasers provides an independent absolute calibration of cross sections. Measurements of more than twenty useful two-photon excitation spectra (690-1050nm) have revealed some with large blue shifts of the excitation peak. Two photon excitation spectra of some asymmetric molecules superimpose on the one photon absorption spectra (with wavelength doubled) presumably due to relaxation of parity selection rules in these cases. Most of the tested fluorescent molecules show blue shifted excitation peaks with strongly enhanced cross sections exceeding those observed at twice the one photon absorption. No red shifts of the excitation spectra have been detected. Three photon excitation spectra tend to mimic the one photon absorption spectra. Multi- photon excited emission spectra appear to duplicate the one photon fluorescence emission spectra.
Ultrafast Reactions Involving Small Molecules in Solutions
Authors: Pugliano Nick , Lim Manho , Gnanakaran S. , Hochstrasser Robin M.
Published: February 2023

The study of chemical reactions of small molecules in solution with ultrafast lasers enables properties of the reaction dynamics and product state relaxation to be accurately resolved. The influence of the nonequilibrated solvent can also be examined under conditions in which the timescale of the reactive motion and the vibrational periods of the parent and products is similar or faster than the decay of the solvent correlation function. The two systems that will be presented illustrate the effect of the solvent coordinate on the dynamics of the ensuing reactions. The first reaction involves the dissociation of HgI2 in ethanol through a rapid charge switching process, to the highly polar HgI fragment. In the second example, the water solvated OCT ion dissociates to form O− + Cl, and the subsequent solvation and relaxation of the recombined parent are manifested in the transients.
Role of symmetry breaking in transfer of vibrational coherence from reactant to product
Authors: Gershgoren Erez , Gordon Eli , Star Dimitri , Ruhman Sanford
Published: February 2023

Impulsive photodissociation of triiodide; I3− + hν → I2− + I has been demonstrated to generate vibrationally excited and phase coherent diiodide ion fragments in polar solvents1. Investigations of the mechanisms which allow the phase coherent molecular evolution to transcend bond fission and solvent collisions, stresses the importance of symmetry breaking prior to excitation in molding product vibrational coherence2. Centro-symmetric and linear I3− must decide which of its ends will become the I2− radical, and which atomic iodine. If this decision is postponed too long, collision with solvent may precede it and wash out phase coherence of nuclear motion. Preexisting broken symmetry facilitates a rapid dynamic decision. Subtler effects of a delayed decision involve deposition of excess energy into translation and vibration of the products again show advantages of early symmetry breaking in producing fragment coherence3. The purpose of the present study is to test this hypothesis by comparing dissociation dynamics from centro-symmetric and asymmetrical initial states.
Fiber Optic Reading Magnifiers for the Visually Impaired
Authors: Peli Eli , Siegmund Walter P.
Published: February 2023

Stand magnifiers are popular aids, frequently prescribed in vision rehabilitation services, and are most commonly purchased by patients or their relatives over the counter. Thus, they serve as the only aids for many of the visually impaired who do not gain access to low vision services. The popularity of stand magnifiers is a result of the fact that they are easy to use and simple to learn to use. The fixed object to lens distance provides a stable and focused image at all times. Despite these advantages optical lens stand magnifiers have numerous shortcomings. The main complaint directed at existing stand magnifiers is the need to bend over the magnifier in order to be able to read through it (Spitzberg et al., 1989), which is very tiring for elderly users. The postural problems associated with stand magnifiers also complicate the attainment of proper illumination. The user’s head tends to block light from above, while the need for light access through the sides of the magnifier makes for an uncomfortable and difficult grip. One novel design incorporating a prism to tilt the image's angle has been reported by Spitzberg et al. As is the case with all other optical magnifiers, stand magnifiers are also limited by distortions and vignetting. Typically their field of view is smaller than other equivalent power devices (Cohen & Waiss, 1991), preventing binocular use in most cases.
Images of the Cone Mosaic in the Living Human Eye
Authors: Williams David R. , Miller Don , Morris G. Michael
Published: February 2023

Land and Snyder1 and Jagger2 resolved single photoreceptors through the natural optics of the American garter snake and cane toad, respectively, capitalizing on their large photoreceptors and good optics. It is widely thought that the optical quality of the human eye is too poor relative to the grain of the cone mosaic to resolve photoreceptors in the living human eye. Nonetheless, we show here that when the pupil is large and aberrations are carefully corrected, the cone mosaic can occasionally be seen through the eye's natural optics. In eyes for which the cone mosaic cannot be imaged directly, information about cone spacing can often be obtained from the power spectra of retinal images.
Quantitative Topographic and Tomographic Measurements of the Human Retina by Dual Beam Partial Coherence Interferometry
Authors: Drexler W. , Hitzenberger C.K. , Baumgartner A. , Sattmann H. , Fercher A.F.
Published: February 2023

Direct imaging of the human retina in vivo and quantitative measurements of the thickness of its layers is one of the major challenges of ophthalmic instrumentation during the last years. The diagnostics of several ocular disorders might benefit from the solution of this task. The importance of this task is demonstrated by several recent technical approaches, including stereo video ophthalmoscopy1, laser tomographic scanner2, scanning laser polarimetry3, and optical coherence tomography (OCT)4,5.
Local and Central Visual Eye Growth Control: Defocus vs. Diffuse Image Degradation
Authors: Schaeffel Frank
Published: February 2023

Summary not available.
Models Describing Eccentric Photorefraction Crescents
Authors: Kusel Reinhard
Published: February 2023

After the publication of the research of Howland and Howland1 several authors used eccentric photorefraction to measure refractive errors and accommodation (e.g. Kaakinen2, Norcia et al.3, Bobier and Braddick4, Schaeffel et al.5, Angi and Cocchiglia6) or the development of myopia (Schaeffel and Howland7). But a set-up which can be used by untrained persons and allows automatic examinations of large numbers of subjects is not available in the market. In Europe several scientific working groups and the Italian company Fortune Optical found together to develop an automatic refractometer based on eccentric photorefraction which can be used for screening. In such a set-up it is not sufficient to reduce the image processing on measurements of the crescents’ width, because their inner borders are only unsharply defined, but rather is it necessary to take the total light distribution in the pupil into account.