Train Of Short Pulses Research Articles

Light-driven synchronization of optogenetic clocks

Synthetic genetic oscillators can serve as internal clocks within engineered cells to program periodic expression. However, cell-to-cell variability introduces a dispersion in the characteristics of these clocks that drives the population to complete desynchronization. Here, we introduce the optorepressilator, an optically controllable genetic clock that combines the repressilator, a three-node synthetic network in E. coli, with an optogenetic module enabling to reset, delay, or advance its phase using optical inputs. We demonstrate that a population of optorepressilators can be synchronized by transient green light exposure or entrained to oscillate indefinitely by a train of short pulses, through a mechanism reminiscent of natural circadian clocks. Furthermore, we investigate the system’s response to detuned external stimuli observing multiple regimes of global synchronization. Integrating experiments and mathematical modeling, we show that the entrainment mechanism is robust and can be understood quantitatively from single cell to population level.

Light-driven synchronization of optogenetic clocks.

Synthetic genetic oscillators can serve as internal clocks within engineered cells to program periodic expression. However, cell-to-cell variability introduces a dispersion in the characteristics of these clocks that drives the population to complete desynchronization. Here, we introduce the optorepressilator, an optically controllable genetic clock that combines the repressilator, a three-node synthetic network in E. coli, with an optogenetic module enabling to reset, delay, or advance its phase using optical inputs. We demonstrate that a population of optorepressilators can be synchronized by transient green light exposure or entrained to oscillate indefinitely by a train of short pulses, through a mechanism reminiscent of natural circadian clocks. Furthermore, we investigate the system's response to detuned external stimuli observing multiple regimes of global synchronization. Integrating experiments and mathematical modeling, we show that the entrainment mechanism is robust and can be understood quantitatively from single cell to population level.

Generation of short microwave pulse trains based on a hybrid mode-locked optoelectronic oscillator.

A novel approach, to the best of our knowledge, for generating short microwave pulse trains based on a hybrid mode-locked optoelectronic oscillator (HML-OEO) is proposed and demonstrated. In the proposed scheme, a saturable absorber (SA) device is inserted into the active mode-locked OEO (AML-OEO) to compress the pulse width of the microwave pulse trains. Numerical simulations and experimental results show that the HML-OEO generates a short microwave pulse train with a repetition rate of 98.994 kHz through fundamental frequency mode locking, and its pulse width is compressed by about 50% compared to the AML-OEO. Additionally, in the experiment, microwave pulse trains with different repetition rates are generated by second-, third-, fourth-, and fifth-order harmonic mode locking, respectively. Compared to the AML-OEO, the HML-OEO achieves pulse compression effects of 49.3%, 49.8%, 49.4%, and 49.9%, respectively. Notably, compared to the AML-OEO, the proposed scheme also exhibits outstanding performance in frequency stability.

Quantifying tissue temperature changes induced by infrared neural stimulation: numerical simulation and MR thermometry.

Infrared neural stimulation (INS) delivered via short pulse trains is an innovative tool that has potential for us use for studying brain function and circuitry, brain machine interface, and clinical use. The prevailing mechanism for INS involves the conversion of light energy into thermal transients, leading to neuronal membrane depolarization. Due to the potential risks of thermal damage, it is crucial to ensure that the resulting local temperature increases are within non-damaging limits for brain tissues. Previous studies have estimated damage thresholds using histological methods and have modeled thermal effects based on peripheral nerves. However, additional quantitative measurements and modeling studies are needed for the central nervous system. Here, we performed 7 T MRI thermometry on ex vivo rat brains following the delivery of infrared pulse trains at five different intensities from 0.1-1.0 J/cm2 (each pulse train 1,875 nm, 25 us/pulse, 200 Hz, 0.5 s duration, delivered through 200 µm fiber). Additionally, we utilized the General BioHeat Transfer Model (GBHTM) to simulate local temperature changes in perfused brain tissues while delivering these laser energies to tissue (with optical parameters of human skin) via three different sizes of optical fibers at five energy intensities. The simulation results clearly demonstrate that a 0.5 second INS pulse train induces an increase followed by an immediate drop in temperature at stimulation offset. The delivery of multiple pulse trains with 2.5 s interstimulus interval (ISI) leads to rising temperatures that plateau. Both thermometry and modeling results show that, using parameters that are commonly used in biological applications (200 µm diameter fiber, 0.1-1.0 J/cm2), the final temperature increase at the end of the 60 sec stimuli duration does not exceed 1°C with stimulation values of 0.1-0.5 J/cm2 and does not exceed 2°C with stimulation values of up to 1.0 J/cm2. Thus, the maximum temperature rise is consistent with the thermal damage threshold reported in previous studies. This study provides a quantitative evaluation of the temperature changes induced by INS, suggesting that existing practices pose minimal major safety concerns for biological tissues.

Biophysics-inspired spike rate adaptation for computationally efficient phenomenological nerve modeling

This study introduces and evaluates the PHAST+ model, part of a computational framework designed to simulate the behavior of auditory nerve fibers in response to the electrical stimulation from a cochlear implant. PHAST+ incorporates a highly efficient method for calculating accommodation and adaptation, making it particularly suited for simulations over extended stimulus durations. The proposed method uses a leaky integrator inspired by classic biophysical nerve models. Through evaluation against single-fiber animal data, our findings demonstrate the model’s effectiveness across various stimuli, including short pulse trains with variable amplitudes and rates. Notably, the PHAST+ model performs better than its predecessor, PHAST (a phenomenological model by van Gendt et al.), particularly in simulations of prolonged neural responses. While PHAST+ is optimized primarily on spike rate decay, it shows good behavior on several other neural measures, such as vector strength and degree of adaptation. The future implications of this research are promising. PHAST+ drastically reduces the computational burden to allow the real-time simulation of neural behavior over extended periods, opening the door to future simulations of psychophysical experiments and multi-electrode stimuli for evaluating novel speech-coding strategies for cochlear implants.

Resonant excitation of plasma waves in a plasma channel

We demonstrate resonant excitation of a plasma wave by a train of short laser pulses guided in a preformed plasma channel, for parameters relevant to a plasma-modulated plasma accelerator (P-MoPA). We show experimentally that a train of N≈10 short pulses, of total energy ∼1J, can be guided through 110mm long plasma channels with on-axis densities in the range 1017–1018cm−3. The spectrum of the transmitted train is found to be strongly red shifted when the plasma period is tuned to the intratrain pulse spacing. Numerical simulations are found to be in excellent agreement with the measurements and indicate that the resonantly excited plasma waves have an amplitude in the range 3–10GVm−1, corresponding to an accelerator stage energy gain of order 1GeV. Published by the American Physical Society 2024

Endemic fish calling: Acoustics and reproductive behaviour of the Neretva dwarf goby Orsinigobius croaticus.

The Neretva dwarf goby Orsinigobius croaticus (Gobiiformes, Gobionellidae) is an endemic fish native to the freshwaters of the Adriatic Basin in Croatia and Bosnia and Herzegovina, a Mediterranean Biodiversity Hotspot. Due to its limited distribution range, specific karst habitat and endangered status, laboratory studies on reproductive biology are scarce but crucial. Herein, we investigated the sound production and acoustic behaviour of the endangered O. croaticus during reproductive intersexual laboratory encounters, utilising an interdisciplinary approach. We also performed dissections and micro-computed tomography (μCT) scanning of the pectoral girdle to explore its potential involvement in sound production. Finally, comparative acoustic analysis was conducted on sounds produced by previously recorded soniferous sand gobies to investigate whether acoustic features are species-specific. The endemic O. croaticus is a soniferous species. Males of this species emit pulsatile sounds composed of a variable number of short (~15 ms) consecutive pulses when interacting with females, usually during the pre-spawning phase in the nest, but also during courtship outside the nest. Pulsatile sounds were low-frequency and short pulse trains (~140 Hz, <1000 ms). Male visual behaviour rate was higher when co-occurring with sounds and females entered the male's nest significantly more frequently when sounds were present. Characteristic body movements accompanied male sound production, such as head thrust and fin spreading. Furthermore, μCT scans and dissections suggest that O. croaticus shares certain anatomical similarities of the pectoral girdle (i.e. osseous elements and arrangement of levator pectoralis muscles) to previously studied sand gobies that could be involved in sound production. Multivariate comparisons, using sounds produced by eight soniferous European sand gobies, effectively distinguished soniferous (and sympatric) species based on their acoustic properties. However, the discrimination success decreased when temperature-dependent features (sound duration and pulse repetition rate) were excluded from the analysis. Therefore, we suggest both spectral and temporal features are important for the acoustic differentiation of sand gobies.

Nanoscale reshaping of resonant dielectric microstructures by light-driven explosions

Femtosecond-laser-assisted material restructuring employs extreme optical intensities to localize the ablation regions. To overcome the minimum feature size limit set by the wave nature of photons, there is a need for new approaches to tailored material processing at the nanoscale. Here, we report the formation of deeply-subwavelength features in silicon, enabled by localized laser-induced phase explosions in prefabricated silicon resonators. Using short trains of mid-infrared laser pulses, we demonstrate the controllable formation of high aspect ratio (>10:1) nanotrenches as narrow as {sim }{{{{{boldsymbol{lambda }}}}}}{{{{{boldsymbol{/}}}}}}{{{{{boldsymbol{80}}}}}}. The trench geometry is shown to be scalable with wavelength, and controlled by multiple parameters of the laser pulse train, such as the intensity and polarization of each laser pulse and their total number. Particle-in-cell simulations reveal localized heating of silicon beyond its boiling point and suggest its subsequent phase explosion on the nanoscale commensurate with the experimental data. The observed femtosecond-laser assisted nanostructuring of engineered microstructures (FLANEM) expands the nanofabrication toolbox and opens exciting opportunities for high-throughput optical methods of nanoscale structuring of solid materials.

JS05.6.A CONTINUOUS DYNAMIC MAPPING OF LANGUAGE FUNCTION AND COGNITIVE CONTROL AND SPATIAL CORRELATION TO WHITE MATTER TRACTS USING INTRAOPERATIVE MRI TRACTOGRAPHY

Abstract BACKGROUND Subcortical mapping of white matter tracts (WMTs) subserving complex processes as movement, language and cognition is critical in glioma surgery. Continuous dynamic mapping (CDM) is an indispensable tool for mapping of the corticospinal tract (CST). There is, however, no widespread method for CDM of more advanced brain functions. MATERIAL AND METHODS Patients undergoing awake craniotomy for diffuse gliomas at the Oslo University Hospital with the use of neuronavigation, diffusion tensor imaging (DTI) and CDM coupled with structured evaluation as well as intraoperative magnetic resonance imaging (iMRI) were included in a retrospective analysis. Subcortical CDM was conducted when resection became close to the arcuate fasciculus (AF) and the frontal aslant tract (FAT) with clinical testing using language paradigms and Stroop task. The current was delivered through a monopolar suction probe applying a modified Taniguchi technique with short train of pulses. The spatial relationship between the stimulation response and the examined tracts was determined by measuring the shortest distance between the resection cavity and the relevant white matter tracts (WMTs) using iMRI DTI. RESULTS Twenty IDH-mutant and eight IDH wild type gliomas operated 2021-2023 were included in the analysis. Subcortical CDM of the AF and the FAT proved to be amenable as both language function and the ability to perform Stroop test were affected when the stimulation site gradually became close (&amp;lt; 1 cm) to the examined tracts. Positive stimulation response was verified by repeat challenge. The stimulation intensity was thereafter reduced in a stepwise fashion when there was a consistent hesitation in the patient’s response. Resection was continued until the tumor border was reached and not beyond the threshold of 3mA. The threshold of stimulation intensity correlated to the minimal distance from the resection cavity to the delineated WMTs. We did not observe any seizure activity induced by CDM. CONCLUSION We have experienced subcortical CDM to be a safe and reliable method, where distance to identified WMT appear to be correlated to the applied stimulation intensity.

Stability of the modulator in a plasma-modulated plasma accelerator.

We explore the regime of operation of the modulator stage of a recently proposed laser-plasma accelerator scheme [Phys. Rev. Lett. 127, 184801 (2021)0031-900710.1103/PhysRevLett.127.184801], dubbed the plasma-modulated plasma accelerator (P-MoPA). The P-MoPA scheme offers a potential route to high-repetition-rate, GeV-scale plasma accelerators driven by picosecond-duration laser pulses from, for example, kilohertz thin-disk lasers. The first stage of the P-MoPA scheme is a plasma modulator in which a long, high-energy "drive" pulse is spectrally modulated by copropagating in a plasma channel with the low-amplitude plasma wave driven by a short, low-energy "seed" pulse. The spectrally modulated drive pulse is converted to a train of short pulses, by introducing dispersion, which can resonantly drive a large wakefield in a subsequent accelerator stage with the same on-axis plasma density as the modulator. In this paper we derive the 3D analytic theory for the evolution of the drive pulse in the plasma modulator and show that the spectral modulation is independent of transverse coordinate, which is ideal for compression into a pulse train. We then identify a transverse mode instability (TMI), similar to the TMI observed in optical fiber lasers, which sets limits on the energy of the drive pulse for a given set of laser-plasma parameters. We compare this analytic theory with particle-in-cell (PIC) simulations and find that even higher energy drive pulses can be modulated than those demonstrated in the original proposal.

Optical Time-Mapped Spectrograms (I): From the Time-Lens Fourier Transformer to the Talbot-Based Design

The short-time Fourier transform (STFT), or spectrogram (SP), is the prime method for joint time-frequency signal analysis and processing. Real-time implementation of this powerful tool over instantaneous bandwidths above the GHz range remains challenging. We propose here a universal analog optical processing approach to obtain the STFT of a high-speed temporal waveform (typically, a microwave signal) in a continuous and real-time manner, and with no gaps in the signal acquisition and analysis. The proposed method is based on a photonics time-mapped Fourier transformer, involving temporal modulation of the signal under test (SUT) with a chirped optical pulse (i.e., a time lens) followed by group-velocity dispersion, in which consecutive, overlapping chirped pulses (or time lenses) are utilized for realization of a continuous and gap-free STFT analysis. We derive the design conditions and performance trade-offs of this general scheme, especially concerning its instantaneous bandwidth, time-frequency resolutions and processing speed (number of FTs per second). Moreover, we also show that a previous, simpler time-mapped STFT design based on Talbot effects, in which the SUT is directly sampled with unchirped pulses before dispersion, can be interpreted and evaluated as a particular case of the time-lens STFT scheme introduced here. This suggests a way of implementing an array of overlapping time lenses by simply sampling the SUT with a suitable periodic train of short pulses. The time-lens STFT scheme offers a remarkable versatility to tailor the specifications of the obtained SP, whereas the Talbot design is particularly interesting for SP analysis with enhanced time resolution and ultrahigh processing speed. Our findings are validated through numerical simulations. The proposed method would enable performing the STFT of signals over instantaneous bandwidths above a few tens of GHz, with MHz frequency resolutions and processing speeds exceeding hundreds of millions of FTs per second using realistic fiber-optics technologies.

Sequential absorption of two photons creates a bistable form of RubyACR responsible for its strong desensitization

Channelrhodopsins with red-shifted absorption, rare in nature, are highly desired for optogenetics because light of longer wavelengths more deeply penetrates biological tissue. RubyACRs (Anion ChannelRhodopsins), a group of four closely related anion-conducting channelrhodopsins from thraustochytrid protists, are the most red-shifted channelrhodopsins known with absorption maxima up to 610nm. Their photocurrents are large, as is typical of blue- and green-absorbing ACRs, but they rapidly decrease during continuous illumination (desensitization) and extremely slowly recover in the dark. Here, we show that long-lasting desensitization of RubyACRs results from photochemistry not observed in any previously studied channelrhodopsins. Absorption of a second photon by a photocycle intermediate with maximal absorption at 640nm (P640) renders RubyACR bistable (i.e., very slowly interconvertible between two spectrally distinct forms). The photocycle of this bistable form involves long-lived nonconducting states (Llong and Mlong), formation of which is the reason for long-lasting desensitization of RubyACR photocurrents. Both Llong and Mlong are photoactive and convert to the initial unphotolyzed state upon blue or ultraviolet (UV) illumination, respectively. We show that desensitization of RubyACRs can be reduced or even eliminated by using ns laser flashes, trains of short light pulses instead of continuous illumination to avoid formation of Llong and Mlong, or by application of pulses of blue light between pulses of red light to photoconvert Llong to the initial unphotolyzed state.

Transmission pulse photoacoustic response of thin semiconductor plate

In modern high-speed semiconductor electronics, there is a high-rate heating of components that is affected by very fast relaxation processes. The relaxation times of these processes should be known for thermal management of these devices. For almost half a century, photoacoustic techniques have been successfully developed and used to investigate physical semiconductor properties. In order to enable observation of fast relaxation processes, the model of pulse photoacoustic signal is proposed that includes influence of thermal relaxations. It is shown that these processes can be observed in a thin semiconductor layer by choosing the frequency of short pulse train and their duty cycle.

Photonically Cured Solution-Processed SnO2 Thin Films for High-Efficiency and Stable Perovskite Solar Cells and Minimodules

High-throughput fabrication of metal oxide thin films is always a bottleneck for solution-processed perovskite solar cells. Here, we report a rapid photonic curing process, with a well-controlled train of short light pulses, to develop bilayer (colloidal and blocking layer) SnO2 thin films used as electron transport layers in perovskite ((FA0.83MA0.17)0.95Cs0.05PbI2.5Br0.5, 1.62 eV band gap) photovoltaic devices (n–i–p architecture) with an optimized efficiency of 21.1% alongside good ambient and operational (MPPT) stability. The strong dependency of the photonic curing pulse parameters on device properties is investigated, and we established a corroboration between the chemical properties of the as-cured SnO2 and the optoelectronic performance of the devices and the interface quality. Furthermore, we show that the futile removal of the chloride species in photonically cured SnO2 is an added advantage against the thermally annealed ones regarding charge transport and lower interfacial recombination. Furthermore, the process is impeccably scaled up to demonstrate a series-connected minimodule (16 cm2) with 18.2% efficiency.

When the SAINT goes marching in – A novel transcranial magnetic stimulation protocol shows miraculous promise

IntroductionTranscranial Magnetic Stimulation (TMS) is a non-invasive neuromodulation tool with a growing body of clinical evidence demonstrating positive outcomes in patients with treatment-resistant depression (TRD) as sole or adjuvant therapy. Theta-burst stimulation (TBS), specifically intermittent TBS (iTBS), uses short intermittent pulse trains to cut each session’s duration to 10% of the original repetitive TMS protocol sessions, making it a more appealing option given that it shows similar efficacy. Nevertheless, the number of sessions required remains the same, with a single protocol lasting around 4 to 6 weeks, or longer. However, a new protocol has very recently been approved by the FDA for application in TRD, called the SAINT (Stanford Intelligent Accelerated Neuromodulation Therapy), which reduces treatment duration to 5 days.ObjectivesTo ascertain what evidence supports the SAINT protocol and its efficacy by reviewing available published literature.MethodsA PubMed database search was performed and the main findings of selected studies were summarized.ResultsThree articles were found, which consisted of clinical trials with small study samples of TRD patients. One study found a 90% remission rate after the aforementioned 5-day treatment regimen, with another reporting a 79% response rate after a double-blinded trial. All studies reported no difference in tolerability compared with regular iTBS protocols.ConclusionsThe SAINT protocol shows promising preliminary results, with efficacy, tolerability and safety of use comparable with that of TMS protocols already in use. The reduction in treatment duration that this intensive option is based on is a significant improvement for applicability in clinical practice, which might increase patient compliance and offer quicker results. Further studies are required to evaluate whether the remission rates are maintained in the long term.Disclosure of InterestNone Declared

Low threshold Kerr solitons.

Pumping a nonlinear optical cavity with continuous wave coherent light can result in generation of a stable train of short optical pulses. Pumping the cavity with a non-degenerate resonant coherent dichromatic pump usually does not produce a stable mode-locked regime due to competition of the oscillations at the pump frequencies. We show that generation of stable optical pulses is feasible in a dichromatically pumped cavity characterized with group velocity dispersion optimized in a way that the group velocity value becomes identical for the generated pulses and the beat note of the pump harmonics. The power threshold of the process drops nearly four times in this case and the produced pulses become sub-harmonically locked to the dichromatic pump harmonics. The process is useful for generation of broadband optical frequency combs and optical time crystals.

L-band dual-comb based on gain-switched lasers for CO2 monitoring

This paper reports the development of a dual-comb spectroscopy system based on gain-switched single-mode laser diodes emitting at 1572 nm. The switching is performed by a train of short electrical pulses at a repetition rate of 100 MHz while the lasers are subjected to external optical injection. Under these conditions, broad and Hat optical frequency combs (OFC) are generated, showing 500 tones within 10 dB and a line spacing fix ed by the repetition rate of the swi tching pulses. The dual-comb gene rated by th e interference of two such combs with slightly different line spacing, is used for measuring the absorption line of CO2 at 1572.02 nm. The transmission spectrum is analyzed and fitted to a Voigt profile. A deviation of 3% in the residuals of the fitting is obtained, denoting the high spectral performance of the spectroscopy system.

Production of copper nanoparticles in the process of target ablation by radiation Cr3+:BeAl2O4 laser

The work is devoted to the synthesis of nanoparticles in the process of ablation of a copper target in a liquid by repetitively pulsed laser radiation. It has been noted that nanomaterials based on certain metals have unique physical and chemical properties. This ensures their use in various applications. In particular, copper nanoparticles are successfully used in medicine and biochemistry. To carry out the synthesis of copper nanoparticles, a previously developed Cr3+:BeAl2O4 laser is used. The laser is based on a plane-parallel resonator with a dispersive prism. Using a prism, the radiation wavelength is smoothly adjusted. To carry out copper ablation, the laser generation wavelength was tuned to 740 nm. It has been shown that when a target is exposed to a microsecond laser pulse consisting of a train of short pulses, copper nanoparticles of various sizes are formed. Comparison of the results with the results of previous works shows that exposure of the target to radiation with a shorter wavelength, commensurate with the energy density of the train and similar spatial parameters leads to a decrease in the average size of the synthesized nanoparticles.

State-selective probing of CO2 autoionizing inner valence Rydberg states with attosecond extreme ultraviolet four-wave-mixing spectroscopy

Nonlinear spectroscopies can disentangle spectra that are congested due to inhomogeneous broadening. In conjunction with theoretical calculations, attosecond extreme ultraviolet (XUV) four-wave-mixing (FWM) spectroscopy is utilized here to probe the dynamics of autoionizing inner valence excited Rydberg states of the polyatomic molecule, ${\mathrm{CO}}_{2}$. This tabletop nonlinear technique employs a short attosecond XUV pulse train and two noncollinear, few-cycle near-infrared pulses to generate background-free XUV wave-mixing signals. FWM emission is observed from the $n=5--7$ states of the Henning sharp $nd{\ensuremath{\sigma}}_{g}$ Rydberg series that converges to the ionic $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{B}\phantom{\rule{4pt}{0ex}}^{2}\mathrm{\ensuremath{\Sigma}}_{u}^{+}$ state. However, these transient emission signals decay with lifetimes of 33 $\ifmmode\pm\else\textpm\fi{}$ 6, 53 $\ifmmode\pm\else\textpm\fi{}$ 2, and 94 $\ifmmode\pm\else\textpm\fi{}$ 2 fs, respectively, which calculations show are consistent with the lifetimes of the short-lived $n=6--8$ members of the $ns{\ensuremath{\sigma}}_{g}$ character Henning diffuse Rydberg series. The oscillator strengths of transitions between states involved in all possible resonant FWM processes are calculated, verifying that the nonlinear spectra are dominated by pathways described by an initial excitation to the diffuse $ns{\ensuremath{\sigma}}_{g}$ Rydberg series and emission from the sharp $nd{\ensuremath{\sigma}}_{g}$ Rydberg series. The results substantiate not only that attosecond XUV FWM spectroscopy produces rigorous and meaningful measurements of ultrafast dynamics in polyatomic systems, but also that nonlinear spectroscopic techniques are versatile tools to selectively probe dynamics that are otherwise difficult to access.

Passive mode-locked cesium diode-pumped alkali laser.

A first, to the best of our knowledge, demonstration of passive mode-locking in diode-pumped alkali laser (DPAL) is reported in this paper. An intracavity cesium vapor cell, buffered by atmospheric pressure methane, is used to passively mode lock a continuously pumped cesium DPAL with a static gain medium. A train of short pulses with duration less than 460 ps was observed using a 2.0-GHz bandwidth detector that limited the real time duration measurements. The calculated minimum duration for these pulses is 57 ps.