Peak Of Laser Pulse Research Articles

Optimization of dispersions in benzene-core square photonic crystal fibers for mid-infrared supercontinuum generation with very low peak power

An ultra-broadband, very low peak power supercontinuum source is proposed based on a novel benzene-filled structured photonic crystal fiber. The modification of the structural parameters has been highly effective in improving dispersion properties, an ultra-flat all-normal dispersion is achieved with fluctuations of ±1.174 ps/(nm.km) in the 0.458 µm wavelength region. Three fibers with suitable optical properties best meet the requirements of supercontinuum generations with low peak power based on numerical simulation results. With anomalous dispersion regime, the first fiber offers the supercontinuum spectra in the mid-infrared region spanning from 0.784 µm to 3.973 µm (2.539 µm bandwidth at 30 dB) using laser pulses excited at 1.55 µm has a peak power of 150 W. A pulse with a peak power of 280 W propagates in a 5 cm length of the second fiber results in a supercontinuum spectrum covering from 0.744 µm to 1.859 (bandwidth 1.063 µm at 30 dB) at a pump wavelength of 1.3 µm with all-normal dispersion regime. A smooth, highly coherent supercontinuum spectrum spanning from 0.843 µm to 2.517 µm (bandwidth at 30 dB of 1.608 µm) is achieved when the third fiber has all-normal ultra-flat dispersion profile pumped at 1.75 µm wavelength with laser pulse peak power of 350 W. With very low peak power, these proposed three-fiber based broadband supercontinuum sources could be a low-cost alternative to traditional glass-core fiber, which has great potential for mid-infrared spectroscopy.

Electronic Population Reconstruction from Strong-Field-Modified Absorption Spectra with a Convolutional Neural Network

We simulate ultrafast electronic transitions in an atom and corresponding absorption line changes with a numerical, few-level model, similar to previous work. In addition, a convolutional neural network (CNN) is employed for the first time to predict electronic state populations based on the simulated modifications of the absorption lines. We utilize a two-level and four-level system, as well as a variety of laser-pulse peak intensities and detunings, to account for different common scenarios of light–matter interaction. As a first step towards the use of CNNs for experimental absorption data in the future, we apply two different noise levels to the simulated input absorption data.

On modelling Nd:Yag nanosecond laser milling process by neural network and multi response prediction methods

In this paper, the milling effects on AISI 316 L steel by nanosecond pulsed laser was studied under different parameters as laser pulse peak power, laser repetition rate, scanning speed and focal point. Based on a full factorial design, 108 tests were conducted. MD varied from 15.58 to 60.14 µm; MRR from 0.0028 to 0.0195 mm3/s; Ra from 0.13 to 1.49 µm. The study showed that the laser power and scanning speed have a great influence on material removal. When the laser spot was focused on the upper sample surface, the removing material process was improved. Moreover, Response Surface Methodology and Artificial Neural Network were used to analyze and predict the milling depth, the material removal rate, and the surface roughness. The predictive capabilities of the methods were compared. The predicted R-square for RMS model were 99.70%, 77.79% and 67.73%, while for FF-BPNN were 99.99%, 99.85% and 81.98% for MD, MRR and Ra respectively. Therefore, both models demonstrated strong ability to match the responses. Neural network model exhibited superior predictive power.

The role of laser chirp in relativistic electron acceleration using multi-electron gas targets

The role of multi-10 TW chirped laser pulses interacting with N2 gas jet targets, as a test case for multi-electron targets, is experimentally examined. Complementary measurements using He gas jet targets, which are fully ionized well before the laser pulse peak, are also presented for comparison with the measurements for the multi-electron N2 targets. It is found that for both gases positively chirped laser pulses accelerate electrons more efficiently compared to the Fourier transform-limited and negatively chirped pulses. Furthermore, multi-electron targets offer additional electron injection mechanisms for efficient electron acceleration as a function of the chirp, due to the dynamic ionization of inner-shell electrons near the peak of the laser pulse. Finally, we show that the background plasma density value plays a critical role in the efficient acceleration of positively chirped pulses as well as in the tuning of the positive chirp value for maximizing the electron energy. We clearly observe that larger plasma density values require higher positive chirp values for efficient electron acceleration.

Improving focusability of post-compressed PW laser pulses using a deformable mirror

The use of the post-compression technique ensures gain in laser pulse peak power but at the same time degrades beam focusability due to the nonlinear wavefront distortions caused by a spatially nonuniform beam profile. In this paper a substantial focusability improvement of a post-compressed laser pulse by means of adaptive optics was demonstrated experimentally. The Strehl ratio increase from 0.16 to 0.43 was measured. Simulations showed that the peak intensity in this case reaches 0.52 of the theoretical limit.

Electron quantum path control in high harmonic generation via chirp variation of strong laser pulses

The quantum phases of the electron paths driven by an ultrafast laser in high harmonic generation in an atomic gas depends linearly on the instantaneous cycle-averaged laser intensity. Using high laser intensities, a complete single ionisation of the atomic gas may occur before the laser pulse peak. Therefore, high harmonic generation could be localised only in a temporal window at the leading edge of laser pulse envelope. Varying the laser frequency chirp of an intense ultrafast laser pulse, the centre, and the width of the temporal window, that the high harmonic generation phenomenon occurs, could be controlled with high accuracy. This way, both the duration and the phase of the electron trajectories, that generate efficiently high harmonics, is fully controlled. A method of spectral control and selection of the high harmonic extreme ultraviolet light from distinct quantum paths is experimentally demonstrated. Furthermore, a phenomenological numerical model enlightens the physical processes that take place. This novel approach of the electron quantum path selection via laser chirp is a simple and versatile way of controlling the time-spectral characteristics of the coherent extreme ultraviolet light with applications in the fields of attosecond pulses and soft x-ray nano-imaging.

Demonstration of Single‐Shot Measurements of 1013 Ultrahigh‐Contrast Pulses by Manipulating Cross‐Correlation

In strong‐field physics experiments with high‐intensity lasers, single‐shot characterization of the temporal contrast between the laser pulse peak and its temporal pedestal is important; this allows fast optimization of the pulse contrast and meaningful comparison with theory for each pulse shot. To date, high contrast ratios of 1010 have been demonstrated in single‐shot measurements for petawatt (PW) lasers. However, ultrahigh contrast ratios of ≈1013, as required for the planned 200 PW lasers, pose challenges to high‐intensity laser technologies and have thus far remained open for investigation. This article reports a pilot demonstration of ultrahigh‐contrast measurements by adapting a single‐shot cross‐correlator (SSCC). An evaluation method for the SSCC detection limit is introduced. The strategy mimics the test beam with known spatial contrast, whose cross‐correlation is equivalent to that of a test pulse with ultrahigh temporal contrast. The ultimate contrast measurement limit of 1013 is achieved, which corresponds to the highest pulse intensity by optical damage and the lowest temporal pedestal by single‐photon detection. The photon noise of the detector is observed and becomes dominant as the temporal pedestal of the optical pulse decreases. The demonstrated detection ability is applied to a high‐contrast laser system, suggesting the accessibility of ultrahigh‐contrast measurements.

Saturation of electron emission with increasing ultrarelativistic intensity of the Gaussian laser pulse

Symmetric electron trajectories in the field of a Gaussian laser pulse are calculated as trajectories with compensation of the dynamic shock at the initial instant of motion. It is shown that the symmetric trajectories have an extremal property, namely, at a fixed peak intensity of the pulse, the time dependence of the electron emission intensity from a symmetric trajectory has the maximum width and amplitude compared to all other trajectories. Formation of paired peaks of electron emission intensity with changing laser pulse peak intensity is analyzed. It is found that the electron emission energy saturates with increasing peak intensity of the laser field in the ultrarelativistic region.

Betatron-type laser-plasma x-ray sources generated in multi-electron gas targets

Betatron-type laser-plasma x-rays are recorded simultaneously with their corresponding relativistic electron spectra in a laser wakefield acceleration scheme. The role of the multi-electron gas target in the betatron-type x-ray efficient generation is experimentally examined. A proof of principle experimental study shows that by using a multi-electron gas target and appropriately adjusting the pumping laser intensity an increase in betatron-type x-rays efficiency could be achieved. This is attributed to sophisticated control of the type of the electron injection inside the plasma bubble related to the tunneling ionization process occurring after the laser pulse peak. This method depends primarily on the gas target charge state chosen for attaining the ionization injection scheme and could be extended to a wide range of relativistic laser intensities.

High-Power and Repetion Rate Nanosecond Pulse Generation in “Diode Laser—Thyristor” Stacks

The “laser diode mini-bar (LDMB) – multi-element thyristor array (META)” vertical stack design is developed and its optoelectronic characteristics are studied. It is shown that adding a highly-doped layer to a low-voltage thyristor p-base leads to an increase in the repetition rate up to 1 MHz at nanosecond laser and current pulses. Laser pulses with 11.5 W peak power and 2.4 ns pulse width at 1 MHz repetition rate are demonstrated using the META chip, comprised of 4 elements, as a high-current switch. It is shown that the difference between LDMB elements’ turn-on delays does not exceed 400 ps. An increase in the pulse repetition rate from 10 kHz to 1 MHz at the operating voltage of 25 V is accompanied by insignificant LDMB heating (up to 3 °C) and a slight decrease in the laser pulse peak power (from 11.5 W to 11.1 W).

Laser-Driven Programmable Metal Transfer in GMAW

Conventional pulsed laser-enhanced gas metal arc weld-ing (GMAW) employs a single fiber laser focused and aimed on the droplet neck position to produce a laser recoil force and thus ensure the droplet detachment despite the am-perage of the welding current. One drop per laser pulse metal transfer is obtained, and the droplet deflects away from the wire axis along the laser incident direction. This implies that the droplet trajectory may also be controlled if the direction of the laser recoil force can be adjusted. Such a controllability is expected to bring an entirely new capa-bility to the GMAW process: active control on the weld beam geometry. To this end, double-sided, laser-enhanced GMAW was proposed and experimentally verified in this pa-per. The two lasers were symmetrically positioned, and both aimed at the droplet neck. The laser pulse peak power, du-ration, and pulse phase of the two lasers can all be programmed to regulate the laser recoil forces. The metal transfer under twin laser irradiations (same laser pulses and phases) was first verified. Then the effectiveness on controlling the droplet trajectory of three proposed control strategies — peak power matching, peak width matching, and phase matching of the two lasers — were evaluated. The results showed laser peak power matching is optimal for obtaining desired droplet trajectory. Since the laser can be easily controlled in real time, the transfer frequency, droplet size, and trajectory can all be adjusted in real time, and the metal transfer evolves into programmable transfer.

Initial Test of Optoelectronic High Power Microwave Generation From 6H-SiC Photoconductive Switch

High-power photoconductive semiconductor switch (PCSS) working in linear mode can be used for RF generation by modulating the illuminating light. This letter presents a design and initial test of an optoelectronic class B push-pull microwave power amplifier (MPA) using two 6H-SiC photoconductive switches. The initial tests have been conducted with bias voltage of ±2.4 kV, at 80 kW peak laser pulse power, demonstrating that the SiC PCSS working in linear mode can produce microwaves. Then, circuit simulation is conducted to study the factors affecting the electrical efficiency, such as the quantum efficiency, the peak laser pulse power, and the bias voltage. It is speculated that the MPA could output 1 mW microwave power and achieve electrical efficiency of more than 60% with a bias voltage of 15 kV, quantum efficiency of 0.2, and peak laser pulse power of 100 kW.

Implementation and characterization of coating pure titanium dental implant with sintered β-TCP by using Nd:YAG laser

ObjectivesThis work presents laser coating of grade 1 pure titanium (Ti) dental implant surface with sintered biological apatite beta-tricalcium phosphate (β-TCP), which has a chemical composition close to bone. Materials and methodsPulsed Nd:YAG laser of single pulse capability up to 70 J/10 ms and pulse peak power of 8 kW was used to implement the task. Laser pulse peak power, pulse duration, repetition rate and scanning speed were modulated to achieve the most homogenous, cohesive and highly adherent coat layer. Scanning electron microscopy (SEM), energy dispersive X-ray microscopy (EDX), optical microscopy and nanoindentation analyses were conducted to characterise and evaluate the microstructure, phases, modulus of elasticity of the coating layer and calcium-to-phosphate ratio and composition.Results showed that the laser power and scanning speed influenced coating adherence. The cross-sectional field-emission scanning electron microscopy images at low power and high speed showed poor adherence and improved as the laser power increased to 2 kW. Decreasing the scanning speed to 0.2 mm/s at the same power of 2 kW increased adherence. EDX results of the substrate demonstrated that the chemical composition of the coat layer did not change after processing. Moreover, the maps revealed proper distribution of Ca and P with some agglomeration on the surface. The sharp peaks on the X-ray diffraction patterns indicated that β-TCPs in the coat layer were mostly crystalline. The elastic modulus was low at the surface and increased gradually with depth to reach 19 GPa at 200 nm; this value was close to that of bone. The microhardness of the coated substrate increased by about 88%. The laser pulse energy of 8.3 J, pulse peak power of 2 kW, pulse duration of 4.3 min, repetition rate of 10 Hz and scanning speed of 0.2 ms−1 yielded the best results. ConclusionBoth processing and coating have potential use for dental implant applications.

Tunable and passively Q-switched laser operation of Tm:CaYAlO4 between 1848 nm and 1876 nm

Laser emission between about 1850 and 1880 nm is of great interest for neural stimulation applications. We report here on the diode-pumped, continuous-wave and passively Q-switched laser operation of Tm:CaYAlO4 in this specific wavelength domain, for the first time to our knowledge. In the continuous-wave regime, the maximum output power reaches 5.35 W at 1864 nm with a laser slope efficiency of about 40.5%. Using a Cr:ZnSe saturable absorber, passive Q-switching is achieved with a maximum average output power of 2.37 W at 1857 nm. The narrowest laser pulse width is found to be about 59 ns for a repetition rate of 35.3 kHz and the corresponding laser pulse peak power and pulse energy are about 1.145 kW and 67.5 μJ, respectively. By introducing an undoped YAG crystal as intracavity etalon, tunable and passively Q-switched laser operation is obtained between 1848 and 1876 nm while keeping high pulse energies and peak powers.

Electron acceleration by a circularly polarized electromagnetic wave publishing in plasma with a periodic magnetic field and an axial guide magnetic field

In this paper, we study the electron acceleration by a circularly polarized electromagnetic wave propagating through plasma in the presence of a periodic and an axial guide magnetic field. A numerical calculation in MATLAB software was developed by employing the fourth-order Runge–Kutta method for studying the electron energy and electron trajectory in plasma medium. The equations governing the electron momentum and energy which describe electron acceleration by a circularly polarized laser pulse have been obtained. It is shown that by choosing an appropriate wiggler field frequency at short distances, the electron retains an adequate amount of energy. In addition, it is found that due to the simultaneous existence of the wiggler field and field of laser pulse and their combined effects, the electron in the direction of the laser pulse propagating, turns around and subsequently, the electron transverse momentum increases and as a result the electron escapes from the laser pulse near the laser pulse peak. Furthermore, it is seen that by increasing the laser intensity, the electron energy decreases and by decreasing to an appropriate value while employing a wiggler magnetic field, a higher peak of energy is gained.

High energy electrons accelerated in the field of tightly focused relativistic laser pulse for peak intensity evaluation

The action of relativistic femtosecond laser pulse with peak intensity over 1019 W/cm2 onto low density plasma is studied experimentally and numerically. It is demonstrated that electrons may be accelerated up to the relativistic energy (>500 keV) directly by the strong field of tightly focused laser radiation. In dependence on the peak laser intensity a dominant angle of high energy electrons is observed, which is around 45 degree for experimental intensity. On the basis of particles energy and angular distribution the laser pulse peak intensity may be evaluated.

Numerical investigation of the sequential-double-ionization dynamics of helium in different few-cycle-laser-field shapes

We investigate sequential double ionization of helium by intense near-circularly polarized few-cycle laser pulses using a semiclassical ionization model with two independent electrons. Simulated ${\mathrm{He}}^{2+}$ ion momentum distributions are compared to those obtained in recent benchmark experiments [M. S. Sch\offler, X. Xie, P. Wustelt, M. M\oller, S. Roither, D. Kartashov, A. M. Sayler, A. Baltuska, G. G. Paulus, and M. Kitzler, Phys. Rev. A 93, 063421 (2016)]. We study the influence of a number of pulse parameters such as peak intensity, carrier-envelope phase, pulse duration, and second- and third-order spectral phase on the shape of the ion momentum distributions. Good agreement is found in the main features of these distributions and of their dependence on the laser pulse duration, peak intensity, and carrier-envelope phase. Furthermore, we find that for explaining certain fine-scale features observed in the experiments, it becomes important to consider subtle timing variations in the two-electron emissions introduced by small values of chirp. This result highlights the possibility of measuring and controlling multielectron dynamics on the attosecond time scale by fine tuning the field evolution of intense close-to-single-cycle laser pulses.

Laser intensity-based geometry control of periodic submicron polymer structures fabricated by laser interference lithography

Photo-polymerization based fabrication of polymer micro- and nanostructures allows flexible geometry control due to reaction kinetics that are strongly dependent on the characteristics of exposure energy. Herein, we demonstrate the geometry control of the submicron polymer structures by altering the polymerization kinetics with variations of laser pulse duration and peak intensity, simultaneously. Periodic surface structures with submicron features having Gaussian and circle function profiles, as well as unique, dimple-like, geometry nanostructures were fabricated. The demonstrated fabrication method could be applied for the development of diffraction-based optical elements and anti-reflective surfaces, or the modulation of surface wetting and tribological properties.

Laser pulse peak estimation based on photon capture mode of quadrant photodetector

Laser pulse peak estimation theory on quadrant photodetector (QPD) corresponding to all spots center on QPD surface is derived. The model of receiving echoed laser pulse from the target by QPD, and the composite photon detection model containing the inverted parabolic laser pulse and the ambient background noise submitted to Poisson distribution is established. The Cramer Rao lower bound (CRLB) estimation algorithm of laser pulse peak in one quadrant of QPD is derived based on the CRLB theorem. Taking the symmetry of QPD into account, laser pulse peak power CRLBs of each quadrant are calculated for all laser spots center which are located only in quadrant A of QPD, and different coefficients such as the laser pulse width factor and ambient background noise power are considered. Furthermore, the statistical mean and variance estimations of laser pulse peak power are simulated for each quadrant by Monte Carlo simulation method. The results show that: For the same spot center position, laser pulse peak power CRLBs of each quadrant are different. For different spots center positions, CRLBs of one quadrant are also different. The smaller pulse width factor, or the larger ambient background noise, the bigger laser pulse peak power CRLB.

Controlling Chemical Reactions by Short, Intense Mid-Infrared Laser Pulses: Comparison of Linear and Circularly Polarized Light in Simulations of ClCHO+ Fragmentation

Enhanced mode selective fragmentation of oriented ClCHO(+) → Cl + HCO(+), H + ClCO(+), HCl(+) + CO with linear polarized intense mid-IR pulses was demonstrated in our previous computational study ( J. Phys. Chem. Lett. 2012 , 3 , 2541 ). Simulations of angle-dependent strong field ionization of ClCHO indicate the ionization rate in the molecular plane is nearly twice as large as perpendicular to the plane, suggesting a degree of planar alignment can be obtained experimentally for ClCHO(+), starting from neutral molecules. Classical trajectory calculations with a 4 cycle 7 μm laser pulse (peak intensity of 1.26 × 10(14) W/cm(2)) show that circularly polarized light with the electric field in the plane of the molecule deposits more energy and yields larger branching ratios for higher energy fragmentation channels than linearly polarized light with the same maximum field strength. These results suggest circularly polarized mid-IR pulses can not only achieve control on reactions but also provide an experimentally accessible implementation.