Laser Pulse Width Research Articles

Improving ranging performance of SiPM LiDAR in low SNR conditions through an echo processing method and laser pulse modulation

Due to its numerous advantages such as high gain and low operating bias, the silicon photomultiplier (SiPM) holds great potential in LiDAR applications. However, it is more jittery at weak echoes and more sensitive to ambient light, making its ranging performance at low signal-to-noise ratios (SNRs) severely deteriorated. To enhance the ranging performance of SiPM LiDAR under low SNR, a novel echo processing method, to the best of our knowledge, was proposed based on the statistical property of SiPM responses and validated under relatively intensive sunlight (>50klx) using a self-developed LiDAR system. At the same time, laser pulse width modulation and multi-pulse laser emission are used in ranging experiments to maximize the advantages of this method. It has shown that increasing the laser pulse width within a certain range can improve ranging performance, and that emitting multiple laser pulses improves ranging performance more significantly. Utilizing a three-pulse laser with a peak power of only 3.2 W, a target 122 m away was ranged with a precision of 6.53 cm with only five accumulations.

Effect of nanosecond laser pulse width and energy on damage characteristics in carbon fibre reinforced plastic (CFRP) laminates

AbstractThis study explores the effects of laser pulse width and energy on CFRP laminates damage in laser bond inspection technology. Three testing programs were used, including varying laser energy while keeping pulse width constant, altering pulse width while maintaining constant power density, and modifying pulse width while keeping energy constant. The results show that when the pulse width remains constant, increased laser energy has a minimal effect on the initial damage location but leads to gradual interlayer delamination and fiber fracture propagation toward the impact surface. With constant laser energy, a specific threshold for pulse width is observed. When the laser pulse width is below this threshold, it exhibits a positive correlation with the damage characteristics of CFRP laminates, whereas when it exceeds this threshold, it shows a negative correlation. Power density correlates with damage when pulse width is constant, but there is no direct correlation when pulse width varies.Highlights CFRP laminates underwent laser shock tests with varying pulse widths. Power density is positively correlated with damage under specific conditions. There exists a specific threshold for laser pulse width. In single‐sided laser shock, initial damage spreads within a specified range.

A 71 mJ, 300 Hz mid-infrared source based on ZnGeP2 MOPA system

We demonstrated a 71 mJ mid-infrared ZnGeP2 (ZGP) master oscillator power amplifier (MOPA) system that operated at the pulse repetition frequency of 300 Hz. A 2090.6 nm electro-optical Q-switched holmium:yttrium–aluminum-garnet MOPA system with a total energy of 138.3 mJ was used as the pump source of the ZGP-MOPA system. First, based on a ZGP optical parametric oscillator, a mid-infrared laser output of 1.3 mJ was obtained in the state of low-energy pumping. The corresponding beam quality factor M2 was 2.01 × 2.10 (horizontal directions × vertical directions). After two-stage amplification, a mid-infrared laser of 71 mJ was obtained. The pump energy and seed energy of the second ZGP optical parametric amplifier were 92.7 mJ and 23 mJ, the corresponding slope efficiency was 70.3 %. At the maximum output energy level, the pulse width of the mid-infrared laser was 14.6 ns, and the beam quality factor M2 was 3.96 × 3.75.

Amplifying Photon Upconversion in Alloyed Nanoparticles for a Near-Infrared Photodetector.

Photon upconverison has attracted a substantial amount of interest in diverse fields due to its characteristic anti-Stokes emissions. However, obtaining intense emission under low-power laser irradiation has remained a challenge. Here we report a mechanistic design of activator-sensitizer alloyed nanoparticles to achieve bright upconversion under weak infrared irradiation. This design allows a nearest sensitizer-activator separation to facilitate efficient energy transfer that results in remarkably enhanced upconversion (>2 orders of magnitude) under 0.26 W cm-2 irradiation compared to that of the Er sublattice, and the upconversion quantum yield also shows a 20-fold increase. Interestingly, the alloyed nanoparticles exhibit a gradual change in emission color with an increase in Yb3+ content, and moreover, their emission colors can be dynamically controlled by simply modulating the excitation laser power and pulse widths. Such alloyed nanoparticles show great promise for application in a near-infrared photodetector.

Optimization and GRA prediction of Al–Cu pulsed laser welding process based on RSM

In this paper, the process parameters of pulsed laser welding of Al–Cu are studied using response surface methodology (RSM) and grey relation analysis (GRA) to propose optimal directions for lap-shear strength of the joints. A single-factor experiment was conducted to find the suitable process parameter windows. The RSM models were established and analyzed with laser power, welding speed, pulse width, and frequency as inputs and joint lap shear, interfacial weld width, and weld-penetration-depth as outputs. With the use of GRA of interfacial weld width and weld penetration depth with the lap-shear force of joints, the improved direction for the lap-shear force of joints can be proposed.

Indirect confirmation and theoretical application of plasma shock−cavitation principle of pulsed laser shock

The coupling strengthening principle of the double physical effect of plasma shock−cavitation was proposed, and the rationality of the cavitation effect in pulsed laser shock treatment under liquid−confined conditions needs to be confirmed urgently. The XRD testing method and 304 stainless steel, which is easy to obtain diffraction peaks, were selected to quantitatively detect and characterize the residual stress distribution in the action area of a single pulse laser beam. The test results and literature analysis show that the different process conditions of laser shock processing bring about different strength matching of the two stress effects of plasma shock and cavitation, and the main source of stress effect of femtosecond laser shock without coating is the cavitation effect. The actual effects of the laser pulse width and other process parameters such as the absorption layer and the constraint layer affect or determine the material modification principle of the pulsed laser surface treatment.

Experimental study of injection seeded single-longitudinal-mode Q-switched fiber laser

--The role of injection seeding power on the operation and output characteristics of a single-longitudinal-mode (SLM) injection seeded Q-switched fiber laser is investigated. The mode coupling between seeding laser and the potential longitudinal-modes of the oscillator changes as the injection seeding power increase. So the Q-switched laser may operate at different regimes which can be distinguished by the pulse features. Only with a proper range of injection seeding power that is not too larger or too small, the operation of injection seeded Q-switched fiber laser with narrow-linewidth, high peak power and narrow pulsewidth laser pulses is possible. The Q-switched fiber laser linewidth is narrowed through inserting a dual-OCs oscillator into the laser cavity. 200-ns, 1-W peak power SLM Q-switched laser pulse with nearly transform-limited linewidth is obtained when the pump power is 300 mW.

Electromagnetic pulses produced by a picosecond laser interacting with solid targets

A high-power laser ablating solid targets induces giant electromagnetic pulses (EMPs), which are intimately pertinent to laser parameters, such as energy and pulse width. In this study, we reveal the features of EMPs generated from a picosecond (ps) laser irradiating solid targets at the SG-II picosecond petawatt (PSPW) laser facility. The laser energy and pulse, as well as target material and thickness, show determinative effects on the EMPs’ amplitude. More intense EMPs are detected behind targets compared to those at the other three positions, and the EMP amplitude decreases from 90.09 kV/m to 17.8 kV/m with the gold target thickness increasing from 10 μm to 20 μm, which is suppressed when the laser pulse width is enlarged. The results are expected to provide more insight into EMPs produced by ps lasers coupling with targets and lay the foundation for an effective EMP shielding design in high-power laser infrastructures.

Micromachining of functional Ni-Mn-Ga single crystals using femtosecond pulsed laser

Ni-Mn-Ga-based magnetic shape memory (MSM) alloy microactuators have a high potential in miniaturized devices for which conventional mechanisms or materials are no longer feasible. However, manufacturing single-crystal-based Ni-Mn-Ga micro actuators is challenging due to their high brittleness, which precludes conventional machining methods. The present work introduces and develops a novel manufacturing method – femtosecond pulse width laser (FPWL) ablation micromachining – for the manufacture of a functional actuators from oriented Ni-Mn-Ga single crystals. Notably, using a green laser (wavelength 515 nm) permits micromachining in the martensitic phase due to the low heating effect of the process. Optimized FPWL parameters are here used to machine a functional actuator from a five-layered modulated (10 M) martensite Ni-Mn-Ga single crystal. The actuator develops a fully reversible and repeatable magnetic-field-induced strain of 6.5% without any post-processing.

Research on experimental parameter selection for measuring thermal diffusivity by laser flash method at room temperature

Based on the laser flash method, the selection of experimental parameters on the accuracy of measurement results for measuring thermal diffusivity is investigated in this paper. High purity graphite is employed as the experimental material. Three experimental parameters are taken into consideration, including specimen thickness, laser pulse power, and laser pulse width. Firstly, the principle of the laser flash method is introduced. Then, a numerical simulation model is established and independence tests are performed. In order to investigate the impact of different experimental parameters to the precision of the measurement results using the laser flash method, six thicknesses of the specimens, five laser pulse powers, and five laser pulse widths are selected for numerical simulation and LFA 427 measurement experiments. Finally, an orthogonal design method with three-factor and three-level is constructed to investigate the influence degree of these three factors on the measurement results. It is found that the laser pulse width has the most significant influence, while the laser pulse power has the least impact. For high purity graphite specimens, it is required to choose a thicker specimen, a lower laser pulse power, and a smaller laser pulse width to ensure better measurement accuracy.

Theoretical study of influence of laser pulse chirp on terahertz emission characteristics of gas induced by two-color laser field

With the development of terahertz (THz) wave research, the demand for controllable THz sources is increasing. How to obtain the regulated THz waves has been one of the research hotspots and key problem in the field of THz science. There have been researches in which the resulting THz wave is modulated by changing the wavelength, relative phase, energy, or chirp of the laser produced by a two-color laser. In this work, we establish a three-dimensional theoretical model of THz wave generation and subsequent propagation induced by two-color laser. And we investigate the influence of chirp modulation of different laser on THz wave by chirp modulation of the fundamental wave (FW) and the second harmonic wave (SHW) of two-color laser, including THz wave amplitude, THz wave center frequency and spectrum width, and analyze the physical mechanism of related phenomena. At the same time, the effects of different orders of magnitudes of laser chirp parameters (femtosecond and picosecond) and initial phase of laser pulse on THz wave parameters are also studied. The results are shown below. 1) In the two-color laser, the chirp of FW mainly affects the shape of THz wave when the initial phase is unchanged. The chirp modulation of SHW can cause the amplitude of THz wave to change significantly, and affect the center frequency and spectrum width of THz waves. 2) In the case of laser pulse width of femtosecond order, 40 fs is taken as an example. When the chirp parameter is of femtosecond magnitude, the chirp parameter has a great influence on the THz wave generation efficiency of two-color laser filament. At the picosecond magnitude, the chirp parameter has a weak effect on the THz wave energy and mainly affects the phase of the THz wave. 3) The initial phase of the two-color laser can aid in chirp modulation of THz wave to optimize the energy generated. 4) The initial phase of two-color laser can assist in the process of chirped laser modulation of terahertz waves to optimize the energy generated. Our research shows that the chirp modulation, as a controllable parameter, has multiple regulation effect on the properties of radiated THz waves. The related research results provide a new idea and basis for studying the generation and regulation of THz waves.

LIDAR Point Cloud Augmentation for Dusty Weather Based on a Physical Simulation

LIDAR is central to the perception systems of autonomous vehicles, but its performance is sensitive to adverse weather. An object detector trained by deep learning with the LIDAR point clouds in clear weather is not able to achieve satisfactory accuracy in adverse weather. Considering the fact that collecting LIDAR data in adverse weather like dusty storms is a formidable task, we propose a novel data augmentation framework based on physical simulation. Our model takes into account finite laser pulse width and beam divergence. The discrete dusty particles are distributed randomly in the surrounding of LIDAR sensors. The attenuation effects of scatters are represented implicitly with extinction coefficients. The coincidentally returned echoes from multiple particles are evaluated by explicitly superimposing their power reflected from each particle. Based on the above model, the position and intensity of real point clouds collected from dusty weather can be modified. Numerical experiments are provided to demonstrate the effectiveness of the method.

The Effect of Laser Surface Remelting on the Surface Properties of Copper

In order to enhance the wear resistance of copper contacts in high-voltage switches and improve the abnormal discharge phenomenon caused by wear gaps, laser remelting technology was used to strengthen the surface of copper contacts. The surface morphology, microhardness, and wear resistance of the remelted samples were tested and characterized using scanning electron microscopy (SEM), microhardness tester, and friction and wear tester. The test results indicate that laser frequency, pulse width, and energy density parameters can directly affect the surface morphology and wear resistance of the sample, but their influencing processes vary. The laser frequency is achieved by the variation in the superposition relationship between the impact points, while the pulse width and energy density are achieved by the variation in the laser intensity at the impact points. When the pulse frequency is 10 Hz, the pulse width is 10 ms, and the energy density is 132.69 J/mm2, the sample exhibits a more balanced surface morphology, microhardness, and wear resistance.

Investigation of mortality rate of Drosophila melanogaster irradiated with nanosecond passively Q-switched microchip laser

Lasers have been widely used for pest control because they are efficient and effective to kill pests. Efficient pest control has been achieved with pulsed lasers, however, there is less investigation of effects of pulse characteristics on the pest mortality. Here, the effects of laser beam diameter, pulse width, peak power, and repetition rate of a compact passively Q-switched microchip laser on the mortality rate of Drosophila melanogaster have been studied. The lethality dosing for 90% mortality rate (LD90) Drosophila melanogaster has been utilized for evaluating the effects of passively Q-switched laser on mortality of insects. The beam diameter comparable to the size of Drosophila melanogaster is effective and economic for killing insects. The energy fluence required for LD90 decreases about 6.5% as pulse width is shortened from 1.5 ns to 850 ps. The energy fluence required for LD90 decreases about one-third as the peak power of passively Q-switched microchip laser increases four times from 6.94 kW to 27.48 kW. The energy fluence required for LD90 decreases dramatically from 16.02 J/cm2 to 12.77 J/cm2 as repetition rate increases from 5.05 kHz to 9.9 kHz and then tends to keep as a constant around 12.7 kHz with further increase of repetition rate. Nanosecond passively Q-switched microchip laser with high peak power and high repetition rate is a promising light source for effective and efficient pest control.

Plasmon-enhanced optoacoustic transducer with Ecoflex thin film for broadband ultrasound generation using overdriven pulsed laser diode.

Ultrasonic transducers facilitate noninvasive biomedical imaging and therapeutic applications. Optoacoustic generation using nanoplasmonic structures provides a technical solution for highly efficient broadband ultrasonic transducer. However, bulky and high-cost nanosecond lasers as conventional excitation sources hinder a compact configuration of transducer. Here, we report a plasmon-enhanced optoacoustic transducer (PEAT) for broadband ultrasound generation, featuring an overdriven pulsed laser diode (LD) and an Ecoflex thin film. The PEAT module consists of an LD, a collimating lens, a focusing lens, and an Ecoflex-coated 3D nanoplasmonic substrate (NPS). The LD is overdriven above its nominal current and precisely modulated to achieve nanosecond pulsed beam with high optical peak power. The focused laser beam is injected on the NPS with high-density electromagnetic hotspots, which allows for the efficient plasmonic photothermal effect. The thermal expansion of Ecoflex finally generates broadband ultrasound. The overdriven pulsed LD achieves a maximum optical peak power of 40W, exceeding the average optical power of 3W. The thick Ecoflex-coated NPS exhibits an eightfold optoacoustic enhancement with a fractional bandwidth higher than 160% and a peak frequency of 2.5MHz. In addition, the optoacoustic amplitude is precisely controlled by the optical peak power or the laser pulse width. The PEAT-integrated microfluidic chip clearly demonstrates acoustic atomization by generating aerosol droplets at the air-liquid interface. Plasmon-enhanced optoacoustic generation using PEAT can provide an approach for compact and on-demand biomedical applications, such as ultrasound imaging and lab-on-a-chip technologies.

Highly Collimated Monochromatic X-rays Generated by Collision of High-Energy Electrons with Tightly Focused Linearly Polarized Laser Pulse

This article delves into the generation and modulation process of X-rays as high-energy photon sources. Using the principles of classical electrodynamics, this study enables nonrelativistic short pulse lasers to collide with high-energy electrons while the collision center is away from the focal point. This scattering method may produce X-rays with good collimation and monochromaticity, and it progressively approaches inverse Thomson scattering. We studied and analyzed the effects of different electron characteristics and laser parameter settings on the high-energy angular distribution and spectrum of X-rays, especially the setting of the collision center and initial electron velocity, as well as the setting of laser intensity and pulse width. Linear polarized laser pulses with relativistic intensity can generate discrete supercontinuum X-rays with spectral distortion. In addition, the relationships between electronic and laser properties and radiation energy were also studied. Our research can provide valuable insights for manipulating collimated or distorted, monochromatic, or tunable X-rays, as well as understanding their properties.

Effects of machining parameters on Ni-Mn-Ga-based alloys for fabrication of multifunctional micro devices using femtosecond pulse width laser

Ni-Mn-Ga-based magnetic shape memory (MSM) alloy single crystals are known for their large magnetic-field-induced strain (MFIS). This quality makes them a promising material for use in micro actuators and devices. However, the manufacturing of single-crystal-based Ni-Mn-Ga micro actuators is challenging due to their high brittleness and other material properties – numerous machining techniques that are successfully used for the deep engraving of conventional engineering materials cannot be directly applied to Ni-Mn-Ga-based alloys. Nevertheless, previous studies have shown that a femtosecond pulse width laser (FPWL) can be successfully utilized for the defect-free micromachining various materials. This work studies the effects of different engraving parameters and introduces a novel scanning-based method for the deep micromachining of Ni-Mn-Ga-based MSM alloys with maximum surface quality. Results show that a 4-layer strategy with a 0.01 mm hatch distance provides excellent machining in terms of surface quality and dimensional accuracy. This study can be utilized within design stages to estimate minimum margin based on required machined depth and avoid defects that occur in the sample preparation stage. Additionally, evolution of structures generated by FPWL machining are characterized. The results highlight how FPWL can be considered a highly capable process for the micromachining and surface structuring of Ni-Mn-Ga-based single crystals for manufacturing multifunctional MSM microdevices.

Periodical Ultra-Modulation of Broadened Laser Spectra in Dielectrics at Variable Ultrashort Laser Pulsewidths: Ultrafast Plasma, Plasmonic and Nanoscale Structural Effects

Self-phase modulation (SPM) broadening of prompt laser spectra was studied in a transmission mode in natural and synthetic diamonds at variable laser wavelengths (515 and 1030 nm), pulse energies and widths (0.3–12 ps, positively chirped pulses), providing their filamentary propagation. Besides the monotonous SPM broadening of the laser spectra versus pulse energy, which was more pronounced for the (sub)picosecond pulsewidths and more nitrogen-doped natural diamond with its intra-gap impurity states, periodical low-frequency modulation was observed in the spectra at the shorter laser pulsewidths, indicating dynamic Bragg filtering of the supercontinuum due to ultrafast plasma and nanoplasmonic effects. Damping of broadening and ultra-modulation for the longer picosecond pulsewidths was related to the thermalized electron-hole plasma regime established for the laser pulsewidths longer, than 2 ps. Unexpectedly, at higher pulse energies and corresponding longer, well-developed microfilaments, the number of low-intensity, low-frequency sideband spectral modulation features counterintuitively increases, thus indicating dynamic variation of the periods in the longitudinal plasma Bragg gratings along the filaments due to prompt secondary laser–plasmon interactions. The underlying sub- and/or near-wavelength longitudinal nanoscale Bragg gratings produced by femtosecond laser pulses in this regime could be visualized in less hard lithium niobate by atomic force microscopy cross-sectional analysis in the correlation with the corresponding sideband spectral components, supporting the anticipated Bragg filtering mechanism and envisioning the corresponding grating periods.

Rapid synthesis of nanomaterials by solvent-free laser irradiation for energy storage and conversion

Nanomaterials synthesized through laser irradiation have numerous applications in the field of energy storage and conversion. Conventional methods for fabricating nanomaterials often involve extended reaction times, making them susceptible to issues such as reproducibility, impurities, and inhomogeneity. To address these issues, a novel strategy of synthesizing nanomaterials via solvent-free laser irradiation in the gas phase is proposed as a potential solution. This innovative strategy offers ultrafast heating and cooling processes compared to conventional time-consuming methods, resulting in the formation of homogeneous nanosystems within femto- to nanosecond timeframes. The focused laser beam induces rapid photothermal and photochemical effects in either air or an inert gas atmosphere, enabling the rapid production of nanomaterials with precise control over geometry, chemistry, crystallinity, and defect density by adjusting processing conditions and sintering mediums. This review provides insights into the rapid solvent-free laser-assisted synthesis of nanomaterials using natural carbon-based materials, polymers, metal–organic frameworks, and inorganic species in both air and inert atmospheres. The introduction of photo-irradiation across a wide range of precursors facilitates phase transitions and surface functionalization in the resulting nanoproducts. We also discuss the effects of altering laser wavelengths, pulse widths, fluences, and repetition rates on both surface and bulk properties of the final products. Finally, we explore the applications of laser-induced nanomaterials in areas such as rechargeable batteries, supercapacitors, solar cells, and catalysis.

Design and develop an optical setup related to the pump-probe technique for spectroscopic study

In this research, an optical system using Pump-Probe technology was designed to study the effect of changing the Frequency values, integration time, delay time, and laser pulse width on the pumping pulse energy on an arbitrary laser dye material with an absorption coefficient of about 650 nm. we found that decreasing the pumping time to 10% of the pulse time is not suitable for the pump-probe technique because there is no resonance between the pumping time and the detector response to the source used. Also, we indicate that increasing the pumping time to 20% of the pulse time results in the highest possible detector response at an integration time 150 μs in the pump-probe technique. therefore, we noted that the detector response becomes more suitable for working in the pump-probe technique as the pumping time increases, as well as the efficiency of the detector, which increases significantly as the pumping time increases, as well as the integration time for the same delay time, it is more stable at 20% pumping time and collection time 150 μs at a delay time of 12.4 ns.