Short Pulse Research Articles

IR Pulsed Laser Ablation of Carbon Materials in High Vacuum

This work aimed to understand how the energy released by short laser pulses can produce different effects in carbon targets with different allotropic states. The IR pulse laser ablation, operating at 1064 nm wavelength, 3 ns pulse duration, and 100 mJ pulse energy, has been used to irradiate different types of carbon targets in a high vacuum. Graphite, highly oriented pyrolytic graphite, glassy carbon, active carbon, and vegetable carbon have exhibited different mass densities and have been laser irradiated. Time-of-flight (TOF) measurements have permitted the evince of the maximum carbon ion acceleration in the generated plasma (of about 200 eV per charge state) and the maximum yield emission (96 μg/pulse in the case of vegetal carbon) along the direction normal to the irradiated surface. The ion energy analyzer measured the carbon charge states (four) and their energy distributions. Further plasma investigations have been performed using a fast CCD camera image and surface profiles of the generated craters to calculate the angular emission and the ablation yield for each type of target. The effects as a function of the target carbon density and binding energy have been highlighted. Possible applications for the generation of thin films and carbon nanoparticles are discussed.

Determination of Molecular Ground State via Short Square Pulses on Superconducting Qubits

Determination of Molecular Ground State via Short Square Pulses on Superconducting Qubits

The Performance of a New Nanosecond Pulsed Field Ablation Surgical Clamp in Ablation of Cardiac Tissue: A Chronic Porcine Model.

The purpose of this chronic porcine model is to demonstrate safety and efficacy of a new nanosecond pulsed field ablation (nsPFA) parallel clamp in ablating different cardiac tissue. The Pulse Biosciences nsPFA CellFX Clamp System was tested on 6 pigs. Ablations were performed in all four heart chambers by delivering a sequence of very short duration high amplitude electrical pulses taking 1.25 seconds per application independent of tissue thickness or type. Testing for electrical exit block was performed at the time of surgery and at study termination. At 35 days, animals were euthanized and anonymized histopathology was performed to assess lesion width, depth and transmurality. Lesion pattern and general safety was compared to 6 animals in which a bipolar radiofrequency clamp was used (AtriCure Synergy Isolator System). There were no device-related serious adverse events in the nsPFA group. There was one early device related mortality at day 24 in the RFA group from perforation of one of the ventricular ablation sites. There were also two intracardiac thrombotic events with one systemic thromboembolic event in the radiofrequency group. Exit block was confirmed in all animals from both groups for the pulmonary veins and the posterior wall. Histological findings were consistent and demonstrated mature scar formation in all nsPFA ablation specimens, while a 7.1% rate of incomplete histopathological scar maturation was present in the RFA group. In this chronic porcine model, a single 1.25 second application independent of tissue thickness with the CellFX Parallel Clamp System demonstrated promising safety and efficacy profile. All lesions produced by this technology resulted in persistent exit block around pulmonary veins and the posterior atrial wall consistent with a reliable, contiguous and transmural ablation without injury to adjacent organs.

Interplay between classical and quantum dissipation in light-matter dynamics.

A quantum-electrodynamics approach is presented to describe the dynamics of electrons that exchange energy with both photon and phonon baths. Our ansatz is a dissipative quantum Liouville equation, cast in the Redfield form, with two driving terms associated with radiative and vibrational relaxation mechanisms, respectively. Remarkably, within the radiative contribution, there is a term that exactly replicates the expression derived from a semiclassical treatment where the power dissipated by the electronic density is treated as the emission from a classical dipole [Bustamante et al., Phys. Rev. Lett. 126, 087401 (2021)]. Analysis of the distinct contributions to the total radiation shows that the semiclassical emission depends on the coherences, with the remainder of the quantum-electrodynamics driving term determined by the excited populations, thus accounting for the relaxation of eigenstates or incoherent mixed states. This approach is used to investigate the response of the Su-Schrieffer-Heeger model for trans-polyacetylene to both pulsed and continuous laser irradiation. Upon excitation with a short pulse and in the absence of the vibrational mechanism, the conducting band population exhibits a stepwise relaxation, characterized by cycles of exponential decay followed by a transient subradiant state. The latter arises from the collective coupling between Bloch states featuring a quasi-continuum energy spectrum in reciprocal space. The separate examination of the semiclassical dynamics reveals that it is this contribution that is responsible for the collective behavior. If vibrational dissipation is active, following the laser pulse, the excited electrons rapidly populate the minimum of the conduction band, and the emission spectrum shifts to lower frequencies with respect to absorption. Meanwhile, continuous irradiation drives the system to a stationary state with a broad emission spectrum.

Multiscale modeling of short pulse laser induced amorphization of silicon

Silicon surface amorphization by short pulse laser irradiation is a phenomenon of high importance for device manufacturing and surface functionalization. To provide insights into the processes responsible for laser-induced amorphization, a multiscale computational study combining atomistic molecular dynamics simulations of nonequilibrium phase transformations with continuum-level modeling of laser-induced melting and resolidification is performed. Atomistic modeling provides the temperature dependence of the melting/solidification front velocity, predicts the conditions for the transformation of the undercooled liquid to the amorphous state, and enables the parametrization of the continuum model. Continuum modeling, performed for laser pulse durations from 30 ps to 1.5 ns, beam diameters from 5 to 70 μm, and wavelengths of 532, 355, and 1064 nm, reveals the existence of two threshold fluences for the generation and disappearance of an amorphous surface region, with the kinetically stable amorphous phase generated at fluences between the lower and upper thresholds. The existence of the two threshold fluences defines the spatial distribution of the amorphous phase within the laser spot irradiated by a pulse with a Gaussian spatial profile. Depending on the irradiation conditions, the formation of a central amorphous spot, an amorphous ring pattern, and the complete recovery of the crystalline structure are predicted in the simulations. The decrease in the pulse duration or spot diameter leads to an accelerated cooling at the crystal–liquid interface and contributes to the broadening of the range of fluences that produce the amorphous region at the center of the laser spot. The dependence of the amorphization conditions on laser fluence, pulse duration, wavelength, and spot diameter, revealed in the simulations, provides guidance for the development of new applications based on controlled, spatially resolved amorphization of the silicon surface.

Design and implementation of the first proton beam transport line in VEGA-3 Petawatt laser system

Laser–Plasma ion acceleration is acquiring importance on a daily basis due to incipient applicability in certain research fields. However, the energy and divergence control of these brilliant sources can be considered a bottleneck in the development of some applications. In this work, we present the commissioning of a compact proton beamline based on a triplet of quadrupoles dedicated to focus and collect short and energetic pulses, open to the user community. The focused proton beam characterization has been carried out by imaging of scintillation detectors with different particle filters. Experimental results have been compared with numerical simulations performed with Monte Carlo code (MCNP6) and TSTEP that have been used to retrieve the deposited energy, the particle tracking, and the particle distribution in different focal configurations, respectively. Charges of nC ( protons with energies up to 17.25 MeV) have been measured at the focal planes reducing the beam to spot sizes of a few millimetres in RMS (root mean square). The percentage fluctuation of the transported charges values has been studied. Finally, the beam rigidity has been measured by transverse moving of the quadrupoles and subsequent beam centroid shift, allowing to cross correlate the deflected energy with the energy ranges resulting from the filtering process.

Evolution of the liquid/solid interface roughness in Si1-xGex layers processed by nanosecond laser annealing

Pulsed laser annealing is a relevant alternative to conventional thermal processes for future technology nodes as it enables the application of a fast and local thermal budget. Such high-energy process can lead to the formation of a liquid phase that recrystallizes upon heat dissipation, through a high velocity liquid/solid interface moving towards the surface. Here, we report on the evolution of the liquid/solid interface roughness and its influence on the crystallinity of Si1-xGex layers depending on multiple parameters (strain state, doping level, Ge content, and pulse duration). This has been conducted with a roughness quantification method based on cross-section STEM-HAADF micrographs. It has been established that the liquid/solid roughness can be decreased by: (i) a compressive strain decrease, (ii) the use of short duration laser pulses or (iii) a reduction of the initial Ge content. The Ge content and strain must correspond to suitable values for optimized MOSFET performances. Consequently, strain and pulse duration were found to be pertinent levers for liquid/solid interface roughness reduction. Increasing the amount of boron atoms in s-Si1-xGex:B/Si systems is another relevant strategy, as compressive strain decrease would then be associated with a beneficial contact resistance lowering in the source-drain regions of p-type MOSFET devices.

Design of a Novel 16‐Way Short Pulse Power Divider Based on Transmission Line Transformer

ABSTRACTThis article presents a 16‐way short pulse power divider (PD) with the same input and output impedance based on the transmission line transformer (TLT) principle. Different from the traditional multi‐channel PD composed of impedance tapered transmission lines and PDs in parallel structure, the novel 16‐way PD is cascaded by multi‐stages of series‐parallel structure, which avoids the process of impedance transformer and improves the compactness of the device, as well as the transmission efficiency. It was composed of four stages of the novel series‐parallel constructure converted from coaxial waveguide to microstrip line. And to control the energy dissipation, a unified ground of the output ports was built, and the short‐ended metal shell was loaded between every stage. This 16‐way PD was fabricated and measured. The measured return loss of the PD is less than −16 dB from 440 MHz to 6 GHz, and less than −10 dB from 270 MHz to 6 GHz. The measured peak gain is more than 0.83 when input by a Gaussian pulse with tFWHM = 250 ps (FWHM: full‐width half maximum).

A Review on The Nitrogen Laser

Abstract: A nitrogen laser is a type of gas laser that uses molecular nitrogen as its gain medium to operate in the ultraviolet (UV) spectrum. First created in 1963, nitrogen lasers were first put to use in commerce in 1972. A nitrogen laser is a type of gas laser that uses molecular nitrogen as its gain medium to operate in the ultraviolet (UV) spectrum. First created in 1963, nitrogen lasers were first put to use in commerce in 1972.Applications for nitrogen lasers can be found in physics, chemistry, and medical research. The principle of operation for nitrogen lasers is a quick electrical discharge through nitrogen gas. Liquid nitrogen or a gas cylinder might be used to supply the nitrogen gas. The UV-wavelength laser light has a short pulse width and a high intensity. The principle of operation for nitrogen lasers is a rapid electrical discharge via nitrogen gas. Liquid nitrogen or a gas cylinder might be used to supply the nitrogen gas. The laser light has a short pulse width, high intensity, and is released into the ultraviolet spectrum. Electricity is used by the nitrogen laser to excite the nitrogen. The electrons in the laser strike the nitrogen atoms in the air when an electric spark passes through a spark gap, stimulating them into a metastable condition. A photon with a wavelength of 337 nm causes stimulated emission and the creation of a laser state in the excited nitrogen atoms. Electricity is used by the nitrogen laser to excite the nitrogen. The nitrogen atoms in the air are excited into a metastable condition when an electric spark passes through a spark gap in the laser. A photon with a wavelength of 337 nm causes stimulated emission and the creation of a laser state in the excited nitrogen atoms. [22]

Rapid osmocontractile response of motor cells of Mimosa pudica pulvini induced by short light signals.

The Mimosa pudica leaf has motor organs allowing movements driven by cell osmotic changes in the parenchyma cells in response to various stimuli. Short white light pulses induce rapid and large seismonastic-like movements (denoted "photostimulation") of the primary pulvini in various leaves within 120 s after the onset of light. An early event recorded is a wavelength-related modification of the plasma membrane difference: potential depolarization under white, blue, green, and red wavelengths, and hyperpolarization under far red wavelengths (and also in darkness). The photoreactivity of the pulvini is controlled by a circadian rhythm and modulated by the applied diurnal photoperiod cycle (photophase ranging from 6 to 18 h). The reactivity varied among plants and even between leaves on the same plant. The level of reactivity is related to the photon fluence rate in the range from 10 to 140 μmol m-2 s-1 under white light and to the experimental temperature in the range 15°C-35°C. An "accommodation" to light supply is evidenced by a modulation of the reactivity in relation to the schedule of light application under low fluence rates and the introduction of short darkness intervals during the first 30-s light pulse. The blue light-induced photostimulation is under phytochrome control.

Backscatter Signal in Underwater Lidars with a Complexly Modulated Probe Beam

The results of statistical modeling of the backscatter signal in lidars when probing the water column with pulses with internal modulation by complex frequency modulated signals and their matched processing in the receiving path of the lidar are presented. The simulation results are compared with analytical calculations in the small-angle approximation. It is shown that the photons spread along their paths, associated with multiple scattering in the medium, does not prevent effective compression of the complex signal, and the small-angle approximation well describes the energy-carrying part of the signal backscattered by the water column. A comparison was made of the levels of backscatter signals when probing water with a short pulse and a complexly modulated pulse. It is shown that the use of complexly modulated illumination pulses makes it possible to reduce the power emitted by the source while maintaining the level of the backscattering signal in the lidar and its range resolution. Calculations of the levels of the signal backscattered by a localized diffusely reflecting object are performed and it is shown that at a delay value corresponding to the arrival time of ballistic photons, the compressed pulse is not distorted. At long delay times, a pulse tail is formed due to the spread of photons along their paths. An example of calculating the backscattering pulse in the presence of a non-reflecting object in the water is given.

Soliton resolution for the generalized complex short pulse equation with the weighted Sobolev initial data

In this work, the Cauchy problem for the generalized complex short pulse equation with initial conditions in the weighted Sobolev space H(R) is studied by using the Riemann-Hilbert method and the ∂‾-steepest descent method. Based on the spectral analysis of the Lax pair, the solution of the Cauchy problem can be expressed as solution of a Riemann-Hilbert problem, which is transformed into a solvable model after a series of deformations. Finally, the long-time asymptotics and soliton resolution of the generalized complex short pulse equation in the soliton region are obtained by resorting to the ∂‾-steepest descent method. The results also indicate that the N-soliton solutions of the generalized complex short pulse equation are asymptotically stable.

Ultrafast Mapping of Electronic and Nuclear Structure in the Photo Dissociation of Nitrogen Dioxide.

We investigate the photoinduced dissociation reaction of NO2 → NO + O upon electronic excitation of the X̃2A1 (D0) to the Ã2B2 (D1) state by femtosecond X-ray absorption spectroscopy at the nitrogen K-edge. We obtain key insight into the chemical bond breaking event and its associated electronic structural dynamics. Calculations of the photoinduced reaction allow to assign the transient absorption features at time scales of 10-50 fs to wave packet motions in the excited D1 and ground D0 states, followed by the formation of the NO photoproduct with a 255 ± 23 fs time constant. Our analysis shows that there is no direct correlation between the 1s core levels and the electronic ground and excited states transition energies and the bond elongation of NO2, while en route to dissociation toward the NO + O photoproducts, in the transient nitrogen K-edge spectra. However, simulations predict that for a sufficiently short UV pump pulse, the early wave packet dynamics in the D1 electronic excited state occurring within the first 35 fs along the bending and symmetric stretching modes can be directly mapped in the transient X-ray absorption spectra.

Dynamic description of soliton solutions of nonlinear schrödinger equation with higher order dispersion and nonlinear terms

Abstract The article presents an analytical solution for the higher-order nonlinear Schrödinger equation (NLSE), which describes the propagation of short light pulses in monomode optical fibers. Various traveling wave solutions are obtained using the generalized exponential rational function method, a technique with substantial applications in physics and mathematics. Additionally, the parameters leading to the occurrence of optical bright and multipeak solitons in this medium are provided along with their formation conditions. The derived solutions are graphically displayed to enhance the understanding of the model’s physical phenomena. This approach is credible, potent, and successful in solving a wide variety of different models of this kind that arise in the applied sciences. Its robustness, strength, and efficiency make it suitable for addressing various higher-order nonlinear problems in current research fields, extending beyond the models encountered in the applied sciences.

Multi-state broadband spectrum and ultra-short pulse spatiotemporal mode-locked Yb-doped multimode fiber laser

In the multimode fiber laser, a phenomenon of multi-state broadband spectrum and ultra-short pulse spatiotemporal mode-locking (STML) is obtained. The dissipative soliton, multiple pulses, harmonic pulse and bound soliton can be observed by rotating the polarization controllers(PCs). The spectral bandwidth of dissipative soliton is 19.04 nm at the central wavelength of 1039.40 nm, and the pulse width is 3.58 ps, acquiring the widest spectrum and the shortest pulse in an all-fiber dissipative soliton STML laser. As the STML state changes from dissipative soliton to bound soliton, spectral bandwidth decreases slightly. The spectral width and modulation period of the loose bound soliton with central wavelength of 1038.24 nm are 18.03 nm and 0.76 nm, respectively. We realize the conversion between the multiple states, which provides a scheme for the study of nonlinear soliton dynamics.

Rapid estimation of lithium-ion battery capacity and resistances from short duration current pulses

Rapid onboard diagnosis of battery state of health enables the use of real-time control strategies that can improve product safety and maximize battery lifetime. However, onboard prediction of battery state-of-health is challenging due to the limitations imposed on diagnostic tests so as not to negatively affect the user experience and impede normal operation. To this end, we demonstrate a lightweight machine learning model capable of predicting a lithium-ion battery’s discharge capacity and internal resistance at various states of charge using only the raw voltage-capacity time-series data recorded during short-duration (100 s) current pulses. Tested on two battery aging datasets, one publicly available and the other newly collected for this work, we find that the best models can accurately predict cell discharge capacity with an average mean-absolute-percent-error of 1.66%. Additionally, we quantize and embed the machine learning model onto a microcontroller and show comparable accuracy to the computer-based model, further demonstrating the practicality of on-board rapid capacity and resistance estimation.

The breather, breather-positon, rogue wave for the reverse space–time nonlocal short pulse equation in nonzero background

In this paper, by using the Darboux transformation (DT), two types of breather solutions for the reverse space–time (RST) nonlocal short pulse equation are constructed in nonzero background: bounded and unbounded breather solutions. The degenerate DT is obtained by taking the limit of eigenvalues and performing a higher-order Taylor expansion. Then the N order breather-positon solutions are generated through degenerate DT. Some properties of the breather-positon solutions are discussed. Furthermore, rogue wave solutions are derived through the degeneration of breather-positon solutions.

Lie symmetries and invariant solutions for three generalized short pulse equations

Lie symmetries and invariant solutions for three generalized short pulse equations

Experimental evaluation of solitary slugs in a horizontal pipe

In this work the existence of a bi-stable flow regime in a horizontal gas-liquid two-phase flow was experimentally confirmed. In this regime, both stratified and slug flows were found to be stable, and the occurrence of either regime depended on the inlet conditions imposed on the flow. When operating in the bi-stable flow condition, two types of slugs can occur. The first type was obtained by forcing a regular slug flow at the inlet of the horizontal pipe using an uphill section before the inlet. In this case, slugs in the uphill and horizontal sections have similar frequencies. The second type was obtained by forcing a stratified flow at the inlet, and then introducing a short pulse in the liquid flow rate. This triggered a solitary slug in the pipe, which grew linearly with the distance from the inlet. The behavior of the solitary slugs observed experimentally confirms the explanation and the model provided by Belt et al., 2024. The existence of such slugs can represent a threat in operations, since in long flowlines they can become extremely large and flood the downstream process installations. For instance, the experiments showed solitary slugs more than 200 pipe diameters long at a distance of 460 pipe diameters from the inlet. In order to evaluate the conditions under which the solitary slug phenomenon might occur, the extent of the bi-stable flow regime was experimentally determined. Its lower and upper boundaries match reasonably well with the stability conditions for slug flow and stratified flow, respectively, which were calculated within a 1D modeling framework.

Cross-sectional imaging of speed-of-sound distribution using photoacoustic reversal beacons

Photoacoustic tomography (PAT) enables non-invasive cross-sectional imaging of biological tissues, but it fails to map the spatial variation of speed-of-sound (SOS) within tissues. While SOS is intimately linked to density and elastic modulus of tissues, the imaging of SOS distribution serves as a complementary imaging modality to PAT. Moreover, an accurate SOS map can be leveraged to correct for PAT image degradation arising from acoustic heterogeneities. Herein, we propose a method for SOS imaging using scanned photoacoustic beacons excited by short laser pulse with inversion reconstruction. Our method is based on photoacoustic reversal beacons (PRBs), which are small light-absorbing targets with strong photoacoustic contrast. We excite and scan a number of PRBs positioned at the periphery of the target, and the generated photoacoustic waves propagate through the target from various directions, thereby achieve spatial sampling of the internal SOS. By picking up the PRB signal using a graph-based dynamic programing algorithm, we formulate a linear inverse model for pixel-wise SOS reconstruction and solve it with iterative optimization technique. We validate the feasibility of the proposed method through simulations, phantoms, and ex vivo biological tissue tests. Experimental results demonstrate that our approach can achieve accurate reconstruction of SOS distribution. Leveraging the obtained SOS map, we further demonstrate significantly enhanced PAT image reconstruction with acoustic correction.