Short Light Pulses Research Articles

On the Propagation of a Short Light Pulse in a Medium with a Lorentz Contour of the Spectral Gain Line

On the Propagation of a Short Light Pulse in a Medium with a Lorentz Contour of the Spectral Gain Line

Infrared neurostimulation in ex-vivo rat sciatic nerve using 1470 nm wavelength

Objective. To design and implement a setup for ex-vivo optical stimulation for exploring the effect of several key parameters (optical power and pulse duration), activation features (threshold, spatial selectivity) and recovery characteristics (repeated stimuli) in peripheral nerves. Approach. A nerve chamber allowing ex-vivo electrical and optical stimulation was designed and built. A 1470 nm light source was chosen to stimulate the nerve. A photodiode module was implemented for synchronization of the electrical and optical channels. Main results. Compound neural action potentials (CNAPs) were successfully generated with infrared light pulses of 200–2000 µs duration and power in the range of 3–10 W. These parameters determine a radiant exposure for stimulation in the range 1.59–4.78 J cm−2. Recruitment curves were obtained by increasing durations at a constant power level. Neural activation threshold is reached at a mean radiant exposure of 3.16 ± 0.68 J cm−2 and mean pulse energy of 3.79 ± 0.72 mJ. Repetition rates of 2–10 Hz have been explored. In eight out of ten sciatic nerves (SNs), repeated light stimuli induced a sensitization effect in that the CNAP amplitude progressively grows, representing an increasing number of recruited fibres. In two out of ten SNs, CNAPs were composed of a succession of peaks corresponding to different conduction velocities. Significance. The reported sensitization effect could shed light on the mechanism underlying infrared neurostimulation. Our results suggest that, in sharp contrast with electrical stimuli, optical pulses could recruit slow fibres early on. This more physiological order of recruitment opens the perspective for specific neuromodulation of fibre population who remained poorly accessible until now. Short high-power light pulses at wavelengths below 1.5 µm offer interesting perspectives for neurostimulation.

Strain wave pathway to semiconductor-to-metal transition revealed by time-resolved X-ray powder diffraction

One of the main challenges in ultrafast material science is to trigger phase transitions with short pulses of light. Here we show how strain waves, launched by electronic and structural precursor phenomena, determine a coherent macroscopic transformation pathway for the semiconducting-to-metal transition in bistable Ti3O5 nanocrystals. Employing femtosecond powder X-ray diffraction, we measure the lattice deformation in the phase transition as a function of time. We monitor the early intra-cell distortion around the light absorbing metal dimer and the long range deformations governed by acoustic waves propagating from the laser-exposed Ti3O5 surface. We developed a simplified elastic model demonstrating that picosecond switching in nanocrystals happens concomitantly with the propagating acoustic wavefront, several decades faster than thermal processes governed by heat diffusion.

Dithienylethene-Based Photoswitchable Catalysts: State of the Art and Future Perspectives

Dithienylethenes (DTEs) are a rare class of small molecules, which are capable of undergoing photochemical electrocyclization that is rapid, reversible, and most importantly—thermally forbidden. This makes them the ideal scaffold for building catalysts that can be activated and deactivated on demand with short pulses of light of the appropriate wavelength. In the following Perspective, we review the strategies toward achieving photoswitchable control with DTE metal-chelating and organocatalytic ligands, compare their effectiveness with a “dynamic range” metric that we introduce, and highlight the various development milestones. Lastly, we outline potential avenues for further growth of this relatively young field of molecular catalysis.

Two-Photon Photoactivation of Rubi-Gaba for Studying the Role of the Antisecretory Factor in the Modulation of the GABAA Receptor in Rat Cerebellar Granule Cells In Vitro

Caged compounds, widely diffused in neurophysiology, are molecules biologically or functionally inert until a short pulse of light enables them. Illumination releases the caged effector allowing the activation, manipulation, and control of selective biological functions and variations. in particular, 3D two-photon excitation microscopy, coupled with the electrophysiological technique of the patch-clamp in whole-cell configuration, provides a useful tool for studying several neurobiological processes such as the localized, accurate, and specific receptor response of a well-defined neuronal area.

Influence of the constant electric field on the photon emission characteristics of selected utility cultivars of the Camellia plant

The article presents the research results related to the measurement of the reaction biological substance to extortion, which was a permanent field electric. To identify the degree of reaction of a biological substance, the phenomenon of generating short light pulses was used, which was registered with a photomultiplier tube turned on in appropriate measurement path. For the research, dried leaves of the Camellia plant were used, which was subjected to the influence of a constant electric field in two voltage combinations, i.e. 1kV and 3kV, and then, using the method of counting single photons, their number was summed in a 1800-second time interval. Significant differences in the number of registered photons were found between the drought subjected to the action of a constant electric field and the drought, where this interaction was not applied. It should be noted that a differentiation was also noted between the dried plants that were subjected to a constant electric field, but with different voltage. Therefore, it is possible, experimentally confirmed, to parameterize the analyzed substance by measuring the total photon emission and identifying selected properties of the substance based on the photon emission characteristics during the measurement..

Bacteriorhodopsin Photocycle Captured at the Single Molecule Level by HS-AFM

Bacteriorhodopsin (BR) from Halobacterium salinarum has been extensively studied structurally and functionally, and used as a model for light-driven proton pumps. Different techniques have been applied to study the structural intermediates and its dynamic response such as X-ray crystallography, X-ray free electron lasers (XFELs), solid-state NMR, high speed atomic force microscopy (HS-AFM) and more recently time-resolved serial femtosecond crystallography (TR-SFX). In particular, HS-AFM provided insights into the light-activation of BR studying cooperativity between protomers in neighboring trimers and revealed much larger conformational changes than anticipated of the surface exposed loops. In this work, we use two HS-AFM based approaches to characterize the photocycle of the molecule. We apply short light pulses and record HS-AFM line scanning HS-AFM (HS-AFM-LS) to determine the activation time response of the molecule. The activation time is much faster than reported before. Furthermore, under continuous light at different light intensities, we describe the full BR photocycle at the single molecule level and derive an energy landscape of the protein.

Sistema de iluminación para obtención de imágenes optoacústicas basado en LEDs y EDU-CIAA

La obtención de imágenes optoacústicas es una técnica híbrida que se beneficia tanto del rico y versátil contraste óptico como de la alta resolución espacial asociada a la baja dispersión de propagación de las ondas ultrasónicas. Usualmente, se utilizan láseres de elevada energía (> 10 mJ) como fuente de luz los cuales son caros, no portátiles y tienen una baja tasa de repetición (~20 Hz). En los últimos años se ha estado investigando el uso de diodos emisores de luz (LEDs) como sustituto ya que son menos costosos, más confiables y compactos, y pueden proporcionar miles de pulsos en un segundo para obtener imágenes en tiempo real. En esta trabajo se presenta la implementación de un sistema de iluminación basado en LEDs y en el sistema embebido EDU-CIAA que es capaz de emitir pulsos de luz de corta duración (< 1 us), con gran intensidad y elevada frecuencia (> 1 kHz).

Water oxidation by photosystem II is the primary source of electrons for sustained H2 photoproduction in nutrient-replete green algae

The unicellular green alga Chlamydomonas reinhardtii is capable of photosynthetic H2 production. H2 evolution occurs under anaerobic conditions and is difficult to sustain due to 1) competition between [FeFe]-hydrogenase (H2ase), the key enzyme responsible for H2 metabolism in algae, and the Calvin-Benson-Bassham (CBB) cycle for photosynthetic reductants and 2) inactivation of H2ase by O2 coevolved in photosynthesis. Recently, we achieved sustainable H2 photoproduction by shifting algae from continuous illumination to a train of short (1 s) light pulses, interrupted by longer (9 s) dark periods. This illumination regime prevents activation of the CBB cycle and redirects photosynthetic electrons to H2ase. Employing membrane-inlet mass spectrometry and [Formula: see text], we now present clear evidence that efficient H2 photoproduction in pulse-illuminated algae depends primarily on direct water biophotolysis, where water oxidation at the donor side of photosystem II (PSII) provides electrons for the reduction of protons by H2ase downstream of photosystem I. This occurs exclusively in the absence of CO2 fixation, while with the activation of the CBB cycle by longer (8 s) light pulses the H2 photoproduction ceases and instead a slow overall H2 uptake is observed. We also demonstrate that the loss of PSII activity in DCMU-treated algae or in PSII-deficient mutant cells can be partly compensated for by the indirect (PSII-independent) H2 photoproduction pathway, but only for a short (<1 h) period. Thus, PSII activity is indispensable for a sustained process, where it is responsible for more than 92% of the final H2 yield.

Thermographic Inspection of Internal Defects in Steel Structures: Analysis of Signal Processing Techniques in Pulsed Thermography.

This study performed an experimental investigation on pulsed thermography to detect internal defects, the major degradation phenomena in several structures of the secondary systems in nuclear power plants as well as industrial pipelines. The material losses due to wall thinning were simulated by drilling flat-bottomed holes (FBH) on the steel plate. FBH of different sizes in varying depths were considered to evaluate the detection capability of the proposed technique. A short and high energy light pulse was deposited on a sample surface, and an infrared camera was used to analyze the effect of the applied heat flux. The three most established signal processing techniques of thermography, namely thermal signal reconstruction (TSR), pulsed phase thermography (PPT), and principal component thermography (PCT), have been applied to raw thermal images. Then, the performance of each technique was evaluated concerning enhanced defect detectability and signal to noise ratio (SNR). The results revealed that TSR enhanced the defect detectability, detecting the maximum number of defects, PPT provided the highest SNR, especially for the deeper defects, and PCT provided the highest SNR for the shallower defects.

Transversally travelling ultrasound for light guiding deep into scattering media

The application of optical methods for tissue diagnosis, activation, and treatment suffers dramatically from the low accessible depths due to strong light scattering in tissues. Here we demonstrate a method to address this issue by utilizing transient ultrasound waves, travelling transversally to the light propagation direction, to guide light into deeper tissue regions. We study the formation of the ultrasound-induced refractive index structures and waveguides using simple ultrasound field configurations and analyze their effects on the propagation of short light pulses. As a proof of concept, we demonstrate using 5 ns pulses of 532 nm light and Intralipid-20%-based phantoms with mu _{mathrm{s}}^prime up to 4.5 cm−1 a waveguide supported light intensity increase up to the depths of at least 90 mean free paths.

Steady-state stomatal responses of C3 and C4 species to blue light fraction: Interactions with CO2 concentration.

Blue light induced stomatal opening has been studied by applying a short pulse (~5 to 60 s) of blue light to a background of saturating photosynthetic red photons, but little is known about steady-state stomatal responses. Here we report stomatal responses to blue light at high and low CO2 concentrations. Steady-state stomatal conductance (gs ) of C3 plants increased asymptotically with increasing blue light to a maximum at 20% blue (120 μmol m-2 s-1 ). This response was consistent from 200 to 800 μmol mol-1 atmospheric CO2 (Ca ). In contrast, blue light induced only a transient stomatal opening (~5 min) in C4 species above a Ca of 400 μmol mol-1 . Steady-state gs of C4 plants generally decreased with increasing blue intensity. The net photosynthetic rate of all species decreased above 20% blue because blue photons have lower quantum yield (moles carbon fixed per mole photons absorbed) than red photons. Our findings indicate that photosynthesis, rather than a blue light signal, plays a dominant role in stomatal regulation in C4 species. Additionally, we found that blue light affected only stomata on the illuminated side of the leaf. Contrary to widely held belief, the blue light-induced stomatal opening minimally enhanced photosynthesis and consistently decreased water use efficiency.

High Resolution Multimodal Photoacoustic Microscopy and Optical Coherence Tomography Visualization of Choroidal Vascular Occlusion

Photoacoustic microscopy is a novel, non-ionizing, non-invasive imaging technology that evaluates tissue absorption of short-pulsed light through the sound waves emitted by the tissue and has numerous biomedical applications. In this study, a custom-built multimodal imaging system, including photoacoustic microscopy (PAM) and optical coherence tomography (OCT), has been developed to evaluate choroidal vascular occlusion (CVO). CVO was performed on three living rabbits using laser photocoagulation. Longitudinal imaging of CVO was obtained using multiple imaging tools such as color fundus photography, fluorescein angiography, indocyanine green angiography (ICGA), OCT, and PAM. PAM images were acquired at different wavelengths, ranging from 532 to 700 nm. The results demonstrate that the CVO was clearly observed on PAM in both two dimensions (2D) and 3D with high resolution longitudinally over 28 days. In addition, the location and margin of the CVO were distinguished from the surrounding choroidal vasculature after the injection of ICG contrast agent. PAM imaging was achieved using a laser energy of approximately 80 nJ, which is about half of the American National Standards Institute safety limit. The proposed imaging technique may provide a potential tool for the evaluation of different chorioretinal vascular disease pathogeneses and other biological studies.

Simultaneous two-color snapshot view on ultrafast charge and spin dynamics in a Fe-Cu-Ni tri-layer

Ultrafast phenomena on a femtosecond timescale are commonly examined by pump-probe experiments. This implies multiple measurements, where the sample under investigation is pumped with a short light pulse and then probed with a second pulse at various time delays to follow its dynamics. Recently, the principle of streaking extreme ultraviolet (XUV) pulses in the temporal domain has enabled recording the dynamics of a system within a single pulse. However, separate pump-probe experiments at different absorption edges still lack a unified timing, when comparing the dynamics in complex systems. Here, we report on an experiment using a dedicated optical element and the two-color emission of the FERMI XUV free-electron laser to follow the charge and spin dynamics in composite materials at two distinct absorption edges, simultaneously. The sample, consisting of ferromagnetic Fe and Ni layers, separated by a Cu layer, is pumped by an infrared laser and probed by a two-color XUV pulse with photon energies tuned to the M-shell resonances of these two transition metals. The experimental geometry intrinsically avoids any timing uncertainty between the two elements and unambiguously reveals an approximately 100 fs delay of the magnetic response with respect to the electronic excitation for both Fe and Ni. This delay shows that the electronic and spin degrees of freedom are decoupled during the demagnetization process. We furthermore observe that the electronic dynamics of Ni and Fe show pronounced differences when probed at their resonance, while the demagnetization dynamics are similar. These observations underline the importance of simultaneous investigation of the temporal response of both charge and spin in multi-component materials. In a more general scenario, the experimental approach can be extended to continuous energy ranges, promising the development of jitter-free transient absorption spectroscopy in the XUV and soft X-ray regimes.

Unipolar light: existence, generation, propagation, and impact on microobjects

A review is presented of recent works on optical unipolar pulses, whose electric area (integral of the electric field strength over time) is nonzero, which determines the predominant direction of the electric field strength. It is shown that the existence of unipolar pulses does not contradict Maxwell’s equations, and that unipolar pulses can propagate in waveguides. It is emphasised that, along with the spectral, energy, and polarisation parameters, the electric area of short light pulses is also an important characteristic. The unidirectional action of these pulses on microobjects indicates that it is promising to develop methods for generating radiation with such properties. We disciuss methods for the generation, propagation, and interaction of unipolar light with classical and quantum systems, as well as methods for recording the electric area of light pulses.

Photoactivatable Odorants for Chemosensory Research.

The chemosensory system of any animal relies on a vast array of detectors tuned to distinct chemical cues. Odorant receptors and the ion channels of the TRP family are all uniquely expressed in olfactory tissues in a species-specific manner. Great effort has been made to characterize the molecular and pharmacological properties of these proteins. Nevertheless, most of the natural ligands are highly hydrophobic molecules that are not amenable to controlled delivery. We sought to develop photoreleasable, biologically inactive odorants that could be delivered to the target receptor or ion channel and effectively activated by a short light pulse. Chemically distinct ligands eugenol, benzaldehyde, 2-phenethylamine, ethanethiol, butane-1-thiol, and 2,2-dimethylethane-1-thiol were modified by covalently attaching the photoremovable protecting group (8-cyano-7-hydroxyquinolin-2-yl)methyl (CyHQ). The CyHQ derivatives were shown to release the active odorant upon illumination with 365 and 405 nm light. We characterized their bioactivity by measuring activation of recombinant TRPV1 and TRPA1 ion channels expressed in HEK 293 cells and the electroolfactogram (EOG) response from intact mouse olfactory epithelium (OE). Illumination with 405 nm light was sufficient to robustly activate TRP channels within milliseconds of the light pulse. Photoactivation of channels was superior to activation by conventional bath application of the ligands. Photolysis of the CyHQ-protected odorants efficiently activated an EOG response in a dose-dependent manner with kinetics similar to that evoked by the vaporized odorant amyl acetate (AAc). We conclude that CyHQ-based, photoreleasable odorants can be successfully implemented in chemosensory research.

Soliton solutions of the Sasa–Satsuma equation in the monomode optical fibers including the beta-derivatives

The main goal of the present paper is to steer an investigation on the dynamics of soliton solutions of a nonlinear model in the monomode optical fibers. In this respect, first, soliton solutions of the model termed as the Sasa–Satsuma (SS) equation describing the propagation of short light pulses are derived in the presence of the beta-derivatives; then, the dynamics of soliton solutions in the monomode optical fibers is analyzed for different values of the parameter β. The soliton solutions presented in this study are categorized in the most common classes of solitons namely bright and dark soliton solutions.

Kinetics of the luminescence decay of Fe2+ impurity centres in polycrystalline ZnSe upon excitation by an electron beam

The kinetics of the decay of the luminescence of Fe2+ ions is measured at nitrogen temperature in polycrystalline ZnSe excited by a short pulse of accelerated electrons. The time dependence of the luminescence intensity differs from the exponential one, observed upon excitation of luminescence by a short light pulse. The obtained nonexponential dependence is theoretically described. The explanation is based on the quenching effect of the excited state of the Fe2+ ion by free electrons of the volume charge of the current of accelerated electrons in the sample (Auger effect). It was shown that the relaxation of the volume charge after the electron-accelerating voltage is removed makes a significant contribution to the decay kinetics of the impurity luminescence.

Spatial images from temporal data

Traditional paradigms for imaging rely on the use of a spatial structure, either in the detector (pixels arrays) or in the illumination (patterned light). Removal of the spatial structure in the detector or illumination, i.e., imaging with just a single-point sensor, would require solving a very strongly ill-posed inverse retrieval problem that to date has not been solved. Here, we demonstrate a data-driven approach in which full 3D information is obtained with just a single-point, single-photon avalanche diode that records the arrival time of photons reflected from a scene that is illuminated with short pulses of light. Imaging with single-point time-of-flight (temporal) data opens new routes in terms of speed, size, and functionality. As an example, we show how the training based on an optical time-of-flight camera enables a compact radio-frequency impulse radio detection and ranging transceiver to provide 3D images.

On the Propagation of Short Electromagnetic Pulses through Quantum Metamaterials

In this paper, we analyse the propagation of a short light pulse through a 1D quantum metamaterial structure, composed of arranged artificial two-level quantum systems. We set up the model which material substance is treated quantum mechanically, while the electromagnetic pulse is classical. On the basis of the adopted model, we investigate the short light pulse propagation through the structure in dependence on the initial state of irradiated two-level systems, the amplitude of the incident light pulse, and the frequency of the pulse carrier wave. Finally, we determine the regimes when the incident pulse can propagate in undistorted soliton form.