This PDF file contains the front matter associated with SPIE Proceedings Volume 13287, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Sol-gel SiO₂ antireflective (AR) film is an important part of the components in "SG II" high power laser device, which plays a technical support in the inertial confinement fusion experiment. Due to its high porosity and large specific surface, it is susceptible to complex environmental conditions during the operation of the device, including humidity change, which will lead to uncertainty in the results of physical experiments. The degree of influence about humidity conditions on the various key properties of SiO₂ AR film can be systematically understood by tracking and testing the changes in water contact angle (WCA), transmittance, laser induced damage threshold (LIDT), etc. of that under different humidity conditions for about 24 weeks. Results show that the contact angles and transmittances of SiO₂ AR films decrease with increasing humidity. The WCA of the films decrease from 120° to 89.2°, and the peak transmittances decrease by about 0.2% when the relative humidity is 49%, the films had a trend of hydrophilic and becoming thinner. SiO₂ AR films have an improving effect on the surface roughness of components, the surface roughness of the components with SiO₂ AR film is less than 1 nm, and basically not affected by humidity environment. While the LIDTs of SiO₂ AR films increase with the increasing humidity. In order to ensure the long-term stability of the key properties of the components with SiO₂ AR films, the ideal storage and working humidity environment for components with SiO₂ AR films is 24%~49% based on the test results of various performance factors.

The glow-discharge plasma static calibration system described in this study was meticulously designed to address the pressing need for Tunable diode laser absorption spectroscopy (TDLAS) measurements of concentration and temperature parameters involving non-stationary component such as oxygen and nitrogen atoms in the investigation of hightemperature gas effects. Employing high-frequency high-voltage alternating current (HF-HVAC), the system efficiently dissociates low-pressure gas within the discharge tube, swiftly generating a plasma rich in the targeted components. Notably, when a gas mixture consisting of 5% NO and 95% He is introduced into the discharge tube, and the output power of the discharge power supply is optimized to its maximum, alongside maintaining a gas pressure of 200 Pa within the discharge tube, the concentration of metastable oxygen atoms reach 3.66×109 cm-3. However, the detection of absorption peaks corresponding to N atoms was not feasible, attributed to the greater instability of N atoms compared to O atoms. In contrast, when a mixture containing 1% N2, 99% He, and trace amounts of air was introduced into the discharge tube, absorption peaks attributable to both O and N atoms were observed simultaneously. By adjusting both the gas pressure and discharge current within the discharge tube, precise control over the concentration of the targeted component is achieved, facilitating accurate calibration of the modulated laser absorption spectrum. The plasma system furnishes a potent instrument for diagnosing high enthalpy flow fields and contributes to the investigation of hightemperature gas effects.

To investigate the effects of laser intensity and electron initial energy on the motion and radiation properties of high-energy electrons, a model of high-energy electrons interacting with laser pulses was established on the basic equations of electromagnetism. Numerical simulation programs written in MATLAB can help to obtain visualization data of electron trajectories and electromagnetic radiation. The results show that the peak amplitude of the electron impact oscillation increases as the laser intensity increases and show a linear increasing trend; the peak amplitude of the electron oscillation decreases as the initial energy of the electrons increases, and the decrease tends to slow down. When the initial energy of the electron is larger, the polar angle in the direction of maximum radiation is 180°, and the incident laser intensity has very little impact on the change of the radiation angle. Observing the radiation peak, the radiation peak is positively correlated with the incident laser intensity and the initial energy of electrons. The electron energy or laser intensity increasing, and the spectral energy distribution expanding from low to high frequencies. The results provide a theoretical basis for further in-depth study of the effects of laser intensity and electron initial energy on the motion and radiation properties of high-energy electrons.

Quantum Key Distribution (QKD) technology, based on the principles of quantum mechanics, provides theoretically unconditional security for information exchange, enabling effective detection and resistance against potential eavesdropping. QKD is categorized into discrete variable QKD (DVQKD) and continuous variable QKD (CVQKD), with this study focusing on theoretical analysis within the terahertz (THz) spectrum. By comparing the performance of the direct reconciliation homodyne detection protocol with the reverse reconciliation homodyne detection protocol, the secure key rate and transmission distance of the CVQKD system in the 0.1-1THz frequency range are investigated under both atmospheric absorption loss alone and the combined effects of atmospheric absorption loss and free-space path loss. The investigation further underscores the beneficial effects of increased antenna gain in mitigating losses, underscoring the critical role of judicious antenna design in maximizing the performance of QKD systems Furthermore, it reviews the latest international advancements in high-gain antennas within the 0.1-1THz band.

The main research content of this paper is to achieve active-passive dual-loss Q-switched based on a WS₂ saturable absorber (SA) with a thickness of 1.6 nm，thereby optimizing 1.06 μm laser pulse output characteristics. The few layers of WS₂ nano-film material were prepared by combining electron beam evaporation (EBE) with chemical vapor deposition (CVD). The unsaturated absorption loss of the WS₂ sample is 7.3%, the modulation depth (ΔT) is calculated to be 19.2%, and the saturation power intensity(I_sat) was fitted to be 1.64 MW/cm². The prepared WS₂-SA successfully achieved passive Q-switched of the laser. When the pump power is 3 W, the maximum average output power, pulse width, pulse repetition rate, single pulse energy, and peak power are 752 mW, 390 ns, 400 kHz, 1.88 μJ, and 4.82 W, respectively-utilizing the saturable absorption characteristics of WS₂ to reduce the threshold of the acoustic-optic modulator (AOM) active Q-switched laser. Through comparative experiments, it is shown that the attributes of AOM+WS₂ active-passive Q-switched laser have been optimized. When the AOM frequency is 10 kHz, the narrowest pulse width of the dual-loss Q-switched laser is 16 ns, which is 30.4% less than the single AOM active Q-switched laser. The peak power of the active-passive Q-switched laser is 2.24 kW, which is 29.5% higher than the former. The pulse width compression and peak power increase are significant, which is beneficial for the instantaneous energy output of the laser.

Using laser irradiation to remove contaminants from soil is an emerging soil remediation method. The model used in this paper is based on local thermal non-equilibrium, using a carrier gas to simulate the recovery of contaminant gases. Numerical simulations are employed to study the temperature field, the evaporation and condensation of moisture, and the transport of gases within the soil under laser irradiation. The results show that continuous wave laser irradiation can rapidly bring both the gas and solid temperatures in unsaturated porous media to conditions suitable for separating most organic contaminants from the soil. Within the effective influence range of the laser, the phase change of water and the gas's transport speed are enhanced. This model can provide a theoretical basis for laser soil remediation or the interaction between lasers and unsaturated porous media.

The full-spectrum high-precision optical surface is important for advanced laser components, and the Fizeau interferometer serves as a coral tool for evaluating low-frequency surface errors of these surface. In high-precision surface calibrated method, absolute surface calibration are generally employed to calibrate the surface, thus obtaining their absolute surface errors. This paper proposed a novel absolute surface calculation method. Its spectral response capability was studied. Based on Gaussian Power Spectral Density(PSD), random errors of surface are constructed for this method. The method was studied by error analysis, including errors introduced during interpolation, Fourier transforms, rotation angles, and interpolation results with different power spectral densities was studied, which demonstrates that full-spectrum response capability of the absolute surface calibration method meets the high-precision optical surface metrology.

Vortex beam has shown great potential in target rotational motion parameter detection due to it’s unique helical spatial phase structure. The basic principle is the rotational Doppler effect (RDE), which, unlike the classical linear Doppler effect, can be observed even if the moving target does not have a velocity component in the direction of beam propagation, thus effectively extracting target motion information when classical Doppler shift is difficult to observe. The potential of vortex beams to detect the rotational motion parameters of targets has been fully exploited with the intensive research in recent years, including detection of the rotational speed (ω), angular acceleration (a), rotational direction, position of the rotating axis (γ,d) and even the attitude of the rotating object. These studies have accelerated the progress of rotational speed measurement principles based on vortex beams RDE from theory to engineering applications. However, currently most of the information on rotational motion parameters is obtained through frequency transformation of the echo signal, and in the actual detection process, manual interpretation is mainly used to ensure accuracy of the signal, which has disadvantages such as low efficiency and difficulty in large-scale promotion and application. If there is a method that can automatically obtain target speed information directly through time-domain signals, it may greatly advance the process of this technology from theory to practical application. The intelligent extraction based on neural networks provides a new approach to solving this problem. Due to the strong coupling between parameters such as rotational speed, topological charge of vortex beam, and time-domine signals during the detection process, it is possible to simulate the patterns through artificial neural network on the basis of a large amount of detection data, thereby intelligently and accurately extracting of the rotation parameters. In this article, we conduct research on intelligent extraction of target speed motion information based on artificial neural networks. The constructed artificial neural network is trained using a large amount of simulation data, and the neural networks model is verified to achieve high-precision acquisition of target speed information directly based on time-domine signals.

Nanosecond pulsed lasers with high single-pulse energy show significant advantages in industrial fields such as material processing and laser cleaning. However, the traditional free-space or waveguide transmission methods are often limited by high energy loss, transmission distance, and difficulty in realizing flexible transmission in practical applications. This research is dedicated to exploring the realization of efficient, stable and flexible transmission of nanosecond pulsed lasers with high single-pulse energy. By combining the simulation of the effect of the decenter and tilt of the optical fiber on the coupling efficiency with the ZEMAX software, we have solved the problem of the spot defocusing in the horizontal and vertical directions caused by the thermal effect of the slab laser by precisely adjusting and optimizing the spatial positions of the lenses in the focusing system and the beam shaping system. This reduces the energy loss of the laser during the optical fiber transmission process and improves the transmission efficiency and stability. Finally, a 178mJ laser is coupled into an optical fiber with a core diameter of 800μm. The coupling efficiency is as high as 96% with a flexible transmission distance of 15m. Our research provides strong support for the development and application of laser technology.

Laser metal deposition technology has found broad applications in the aerospace and marine industries due to its various advantages in terms of high material utilization and unlimited forming dimension. However, due to its complex deposition variations, it is difficult to model the relationship between the process parameters. This limitation hinders research on its mechanism of action and control, leading to challenges in ensuring the quality of deposition and stability of the process. In this study, the melt pool width controller and the melt pool temperature controller were developed to investigate the relationship modeling, respectively. Laser power was selected as the only process control output. The positive correlation and strong coupling between melt pool width and temperature were experimentally verified. The Gaussian distribution of the temperature field of the deposition process was investigated as the cause of the nonlinear relationship between melt pool width and temperature. The melt pool width and melt pool temperature model obtained from this Gaussian temperature field fits the experimental data well, with an R² coefficient of 0.97. This study is of great significance for the mechanism of melt pool temperature on melt pool width during the deposition process. It also contributes to the integration of micro-property control and geometric accuracy control.

The stability and durability of micro-nano structures is the key to influence the structural materials surface towards practical engineering applications. In this paper, the stability of micro-nano structures fabricated by femtosecond laser is systematically studied. It is found that the hierarchical micro-nano hybrid structures seriously affect absorbing properties and stability of the material surface due to the poor crystallinity. In order to enhance efficient optical absorption and stability, the annealing method is applied to further crystallization of the micro-nano structures. As a result, hierarchical micro-nano hybrid structures with large depth-to-width ratios are fabricated. The experimental results demonstrate that an average reflectance of 3.43% is realized in the waveband of 300-2400nm, and the reduction rate of the reflectance reaches 39.6%. Meanwhile, the water jet impact experiment verifies that the stability of the structure is further improved.

In our study, we delve into the effect of laser beam waist radius variations on the interaction of an ultra-tightly focused laser with off-axis electrons. We find that off-axis collisions are the most common case in our experiments, which highlights the relevance of our study. Under ultra-tight focusing conditions (b₀=Λ₀), the electrons are subjected to a qualitative force that is asymmetric in the x+ axis directions and x -axis directions, leading to trajectory deviations and accelerated oscillations. At the same time, the electron radiated power and spectrum exhibit a clear asymmetry, which gradually diminishes as the beam waist radius increases, with increasing peak radiated power and decreasing full width half maximum. These findings are crucial for the generation of ultrashort pulses, especially in the field of ultrashort optics, and are important for applications utilizing nonlinear inverse Thomson scattering radiation.

To improve the characteristics of nonlinear Thomson scattering radiation, a numerical study is conducted on the motion characteristics and radiation properties of stationary electrons driven by circularly polarized negatively chirped laser pulses with different pulse widths. The results indicate that as the pulse width increases, electron radiation collimation decreases, while the azimuth angle is insensitive to pulse width changes. In the time spectrum, the peak radiation power reaches the order of 10⁸ to 10⁹, showing new characteristics with pulse width variation. The peak radiation power exhibits an extremum rather than increasing with decreasing pulse width, providing a practical method for modulating ultra-short pulse radiation sources. In terms of the observation direction of peak radiation power, the radiation spectrum broadens with increasing pulse width, and radiation monochromaticity decreases, indicating that there is an optimal pulse width for negatively chirped laser pulses that allows strong peak radiation power with minimal monochromaticity attenuation.

In this paper, the motion trajectories, radiation spatial distribution, time spectrum and spectrum distribution of electrons during the interaction between circularly polarized pulses with different chirps are studied. The motion state and radiation distribution during electron and pulse interaction were calculated and obtained by 4-5Runge-Kutta- Fehlberg method (RKF45). The visualization of motion trajectory and radiation distribution is realized by data fitting and MATLAB simulation. The effects of chirp parameters on the radial contraction of electron trajectory, the increase of peak radiation power, the adjustment of peak radiation generation time, and the vortex coupling of radiation spatial distribution are studied. In general, this paper provides an important reference for further understanding and application of chirped pulses in optics and physics by deeply studying the characteristics of electrons under different conditions of Gaussian circularly polarized laser chirped pulses.

Imaging spectrometers can simultaneously obtain spatial and spectral information of targets with high spectral resolution and high spatial resolution. They are widely used in fields such as resource surveys, environmental monitoring, and mineral exploration. Spectral distortion is directly related to data fidelity and is important indicator for evaluating the performance of imaging spectrometers. It mainly includes two main parameters: smile and keystone. In view of the shortcomings of existing spectral distortion measurement methods, such as low accuracy and low measurement efficiency, this paper proposes a multi-field and multi-band spectral distortion measurement method. This method uses a spectral line lamp to illuminate the periodic line target, and images the periodic line target to the incident slit through the relay system. After passing through the spectroscopic system, the small pixel detector receives its spectral signal, and finally completes the measurement of spectral distortion. Using this method, the spectral distortion of the Offner imaging spectrometer is measured. The smile and keystone are 0.30±0.02μm and 0.26±0.02μm, respectively, and its expanded uncertainty is better than the 0.12μm measured by the standard light source method. Experiments show that the method proposed in the paper can effectively improve the accuracy and efficiency of spectral distortion measurement, and provide a technical basis for further performance evaluation and instrument calibration of imaging spectrometers.

Broadband supercontinuum generation in highly GeO₂ doped fibers holds significant appeal for researchers due to their distinct advantages. In this study, we propose employing a low repetition rate noise-like pulse mode-locked fiber laser as the pulse seed for mid-infrared supercontinuum generation in such fibers. Utilizing only one amplifier stage to amplify the noise-like pulse, we achieved a broadband supercontinuum with a 20dB bandwidth spanning from approximately 652nm to 3350nm in a highly GeO₂ doped fiber with a core GeO₂ concentration of 98%, even with an output power as low as 297mW. To the best of our knowledge, this represents the widest supercontinuum achieved in highly GeO₂ doped fibers to date. Additionally, we observed that further increases in pump power resulted in damage to the core of the highly GeO₂ doped fibers. This posed a challenge in expanding the spectral range of the output supercontinuum by simply increasing the peak pulse power. This conclusion is of significant reference value for research on supercontinuum generation based on highly GeO₂ doped fibers.

During laser shock peening, the pulsed laser with high energy is irradiated on the surface of the absorbing coating, after which the laser induces a plasma explosion. The plasma explosion could induce a shock wave with high peak pressure much higher than the yield strength of metal samples so that the plastic deformation can be formed after laser shock peening. After laser shock peening on metal materials, the shock wave could form compressive residual stress near the surface of the sample, which is beneficial for the mechanical properties. The hardness tester is used to measure the hardness of the sample with and without laser shock peening. The results of hardness could be used to analyze the effect of absorbing coating on shock wave. The study of laser shock peening with different absorbing coatings, such as black tape, aluminum tape, and paint coating, could help the application of laser shock peening for metal parts with complex shapes.

Wavefront sensors represent a powerful technique for quantitative phase measurement. This paper presents a single-phase continuous self-imaging grating (SPCSIG) for quadriwave lateral shearing interferometry with high measurement accuracy and high adaptability. The SPCSIG is characterized by a single-stage phase structure with the phase distribution in each period encoded by the macro pixel, which achieves an approximate complex amplitude transmittance. In the simulation, the SPCSIG far field stray light is significantly suppressed. The near field interferograms propagation is stable, and the residuals are close to the theoretical limit. The method is expected to be used in the future such as precision optical metrology, X-ray wavefront sensing, or polymer gratings where hybrid gratings are not suitable.

The advent of three-dimensional integration technology has heightened the demand for high-performance integrated circuits, with Through Glass Via (TGV) emerging as a critical component. This study investigates using femtosecond laser technology to micro-machine transparent and brittle materials, specifically focusing on producing high-quality TGV in JGS1 quartz glass. The research compares various scanning methods and identifies the "Top-down" transmission method as particularly effective for creating TGV with high aspect ratios and minimal thermal effects. The experiment evaluates the impact of laser power, spot overlap rate, and scan count per layer on TGV morphology, optimizing these parameters to develop a processing method suitable for JGS1 quartz and other transparent brittle materials. Results indicate that laser power significantly influences micro-hole diameter, with a power level of around 80mW maintaining a low taper, meeting the requirements for advanced packaging applications. The study also demonstrates the importance of scan count in enhancing TGV roundness and controlling surface defects. By optimizing laser parameters, this research provides an efficient and precise process for quartz glass machining, offering valuable insights for fabricating TGV in three-dimensional integration technology. The findings contribute to developing electronic devices with higher integration and performance. Future research directions include the integration of chemical wet etching, light field modulation, and multi-beam parallel processing to further improve the efficiency and quality of TGV fabrication.

Due to the inhomogeneity of the medium and the scattering effect, phase distortion and intensity attenuation occur during the propagation of light, leading to the inability to obtain clear imaging of the target. Adaptive optics technology can compensate for the influence of scattering media on incident light waves by controlling the phase and amplitude distribution of the incident light. However, existing adaptive optics methods require prior knowledge of the target scene, which to some extent limits the application scenarios of this technology. To address this issue, this study constructs a no-reference image quality assessment system as a fitness metric. It iteratively generates the optimal compensating phase using a Genetic Algorithm(GA), enabling clear imaging of hidden targets in situations where the target scene information is unknown and there are no guide stars. Experimental results demonstrate that the employed no-reference image quality assessment system effectively constrains the optimization process. Specifically, the Energy gradient and Brenner gradient exhibit significant constraint effects in the early stages of evolution, showing a logarithmic improvement in imaging quality. The Tenengrad gradient performs best in the later convergence stage, achieving a peak signal-to-noise ratio(PSNR) of 14.34dB.

Cr₁₂MoV mold steel is one of the important materials for the slide valve pair in aerospace electromechanical servo mechanism. In order to reduce the frictional resistance of the relative contact surfaces of the slide valve pair and improve the transmission efficiency and reliability of the mechanism, a femtosecond laser was used to process micro-texture in the sliding interface of the valve core of the slide valve pair. First of all, in the Cr₁₂MoV mold steel sample surface processing of different depths and morphology of the micro-texture, the use of laser confocal microscopy on the processed surface micro-texture depth and morphology of the test analysis, optimization of the laser processing parameters of the microtexture, and then the optimized laser processing parameters were used to process the micro-texture at the sliding interface of the valve core of the slide valve pair. The results show that: when the single pulse energy is lower than 16.86μJ, the Cr₁₂MoV mold steel can not be effectively removed and processed; when the laser scanning speed is greater than 200mm/s, and the filler spacing is greater than 0.01mm, the texture morphology is incomplete and the bottom roughness is too large. Finally, the laser processing parameters of single pulse energy 16.86μJ, filling spacing 0.01mm and scanning speed 200mm/s were selected to process micro-texture on the sliding interface of the sliding valve auxiliary valve core. Laser confocal microscopy showed that the micro-texture morphology of the valve core sliding interface was complete, the texture depth was about 10μm, and the roughness Ra of the texture bottom was 1.66μm-2.33μm.

In this paper, we designed and fabricated a few-mode fiber (FMF) for writing a long-period fiber grating (LPFG) mode converter to improve its conversion efficiency. First, we used finite element method to simulate the relationship between the period of LPFG and the resonant wavelength. Subsequently, we used the arc discharge method to write LPFGs in FMFs (FMF-LPFGs), and systematically analyzed the relationship between the period numbers and the resonant wavelength. The experimental results showed that the LPFG mode converter could effectively realize the mode conversion from LP₀₁ to LP₁₁ at 1310nm, with a conversion efficiency exceeding 90%. This addresses the gap in the performance of LPFG mode converters at the 1310nm wavelength. The LPFG proposed in this paper demonstrates excellent mode conversion capabilities, providing a solid foundation for its applications in the fields of laser technology, fiber optic communications, and sensing.

The field-integrated snapshot imaging spectrometer, widely used in astronomy, remote sensing, and biomedicine, captures spatial and spectral information simultaneously. Unlike traditional pushbroom systems, these spectrometers require specialized calibration methods due to their unique imaging technique. This paper explores and validates calibration methods tailored for snapshot systems, highlighting their differences from pushbroom methods. Then this paper introduces the working principles of these spectrometers, which utilize a pinhole array, and discusses challenges such as inconsistent dispersion at discrete sampling points, chromatic distortion, and temperature sensitivity. The proposed spectral calibration employs full-spectral monochromatic spots to overcome discrete spectral distribution issues, using pixel coordinate-wavelength fitting to enhance consistency and creating a three-dimensional data cube for real-time spectral recovery. Central wavelength calibration uncertainty is 0.34nm, 6.8% of the standard 5nm spectral resolution, with techniques implemented to counter temperature-induced spectral drift. Finally, a drone airborne experiment was conducted to verify the correctness of the calibration.. This work serves as a technical reference for further development of snapshot imaging spectrometers.

In high-power thulium-doped fiber laser (TDFL) systems with master oscillator power amplification (MOPA) structure, amplified spontaneous emission (ASE) induced self-excited oscillation significantly effects power amplification. Based on the self-built TDFL system, the relationships between the self-excited oscillation and active fiber length, input signal power, fiber bending radius were investigated experimentally. The experimental results show that when the active fiber length decreases from 3.5m to 3.2m, the threshold of self-excited oscillation increases from 107W to 158W, the output laser power increases from 40W to 63W, the optical conversion efficiency increases from 35.75% to 38.73%; when the input signal power increases from 3.9W to 14.7W, the pump power threshold corresponding to the self-excited oscillation increases from 93W to 218W, the output laser power increases from 30W to 98W, the optical conversion efficiency increases from 37.24% to 41.65%; when the bending radius of active fiber decreases from 110mm to 85mm, the self-excited oscillation threshold increases from 185W to 244W, the output laser power increases from 71W to 112W, the optical conversion efficiency increases from 33.97% to 43.53%. The results in this work provide guidance for suppressing self-excited oscillation to further improve the power of TDFL with MOPA structure.

We experimentally demonstrate, for the first time, a 2.8μm femtosecond mode-locked fluoride fiber laser (MLFFL) with switchable pulsed-state including monopulse, dipulse, harmonic mode-locking and soliton molecules. Specifically, through adjustments to the cavity parameters, the mode-locking operation from monopulse to dipulse within a specific pump power range can be realized, with the maximum output power of 165mW and 175mW, respectively. Further increasing the pump power, the operating regime of the oscillator switches to second-order harmonic mode-locking, where the pulse fundamental repetition rate is ~155MHz with the output power of 330mW. In this case, bound soliton molecule can also be acquired by appropriately optimizing the orientation of the waveplates while keeping the pump power fixed. In particular, with increased pump power, multiple states of bound soliton molecule pairs can be achieved as well. The laser system is simple in structure, self-starting and good stability. Our experimental results may provide solutions for practical applications which requiring different pulse state switchable.

Laser-sustained plasma (LSP) source featured by high brightness and wide spectral range is found to be powerful in advanced inspection and spectroscopy applications. Brightness is the key indicator that determines the speed of semiconductor defect inspection. However, the spatial asymmetry of the laser power absorbed by the plasma drives it to grow in the direction of laser incidence, resulting in a decrease in plasma temperature, hence restricting the improvement of brightness. In this paper, we propose an innovative pulse laser-sustained plasma to break through the plasma temperature limitation. Driven by the elevated plasma temperature, the plasma emission power is significantly enhanced. We establish a two-dimensional transient fluid model for LSP to quantitatively construct the relationship between plasma temperature and laser characteristics. The evolution process of LSP is studied systematically through this model. For the first time, we report an important conceptual advance that the use of pulse laser suppresses the defocus displacement of the plasma, thus increasing the plasma temperature conspicuously. Experimental results demonstrate that the plasma emission is enhanced through the entire wavelength range and time period, compared with continuous laser with the same average power. Especially in the ultraviolet band (<400 nm), the enhancement of plasma emission exceeds 50%. This paper establishes a quantitative relationship between laser temporal characteristics and the spatial distribution of plasma temperature, providing theoretical support and experimental verification for achieving high brightness plasma light sources through laser temporal modulation.

We proposed and experimentally demonstrated a tunable L-band narrow-linewidth Brillouin random fiber laser (BRFL) in a half-open ring cavity with Brillouin gain medium of 10-km single mode fiber (SMF) as well as distributed Rayleigh feedback provided by another 20-km SMF. With a low laser threshold of 6.8mW, the proposed laser can realize cavity-mode-free lasing resonance at a wavelength of 1576.08nm, indicating good single-frequency lasing operation. Compared with the Brillouin pump, the frequency noise (FN) of the proposed laser is significantly suppressed by around 30dB, benefiting from randomly distributed Rayleigh scattering along SMF. An ultra-narrow laser linewidth of 400.8Hz is also obtained with a pump/Stokes laser linewidth compression ratio of 87.5, which coincides with theoretical prediction. When the wavelength of the proposed laser is tuned from 1568.08nm to 1576.08nm, sub-kHz random lasers with cavity mode free lasing resonance achieves high optical signal-to-noise ratio (ONSR) operation. The proposed laser source with good tunability has great potentials for practical applications in future advanced optical communication and sensing.

This work investigates the radio-frequency (RF) linewidth characteristics of a single-section quantum dot self-mode-locked laser under a self-injection locking configuration to achieve a stable and compact on-chip pulsed light source. The results indicate an absence of chaotic oscillation and longitudinal mode broadening under the strongest optical feedback conditions. The quantum dot laser exhibits high tolerance to optical feedback, with significant RF linewidth compression, resulting in stable pulse generation. These findings suggest that singlesection quantum dot lasers are promising candidates for on-chip integrated pulsed light sources, offering new opportunities for applications in spectroscopy and quantum optics.

Chirped Tilted Fiber Bragg Gratings (CTFBG) are critical fiber devices used to suppress Stimulated Raman Scattering (SRS) in high-power continuous fiber lasers. To reduce the difficulty of fabrication, optimize the CTFBG transmission spectrum parameters, and enhance its Raman noise suppression capability in the application of higher powers, we designed a dual-angle CTFBG targeting the dual peaks of the Raman gain spectrum. This design, featuring tilt angles of 2.9° and 4.2°, corresponds to transmission spectrum center wavelengths at 13.2THz and 14.7THz. Compared to conventional single-angle CTFBG, the dual-angle CTFBG shows excellent Raman suppression capabilities at both 13.2THz and 14.7THz Raman gain peaks.

To investigate the effects of laser pulses with different polarization parameters on the motion and power radiation distribution of high-energy electrons at different initial positions in the laser field, an electron laser collision model is established on the basis of the basic equations of electromagnetism, and the spatial distribution characteristics of the electron oscillating radiation at different initial positions under different polarization parameters are simulated with the help of MATLAB software analysis. It is shown that with the increase of polarization parameter from 0 to 1, the spatial radiation distribution generated by collision with electrons at different positions shows a bimodal transition to the surrounding area; when the initial position is certain, the radiation distribution gradually decreases and flattens with the increase of the polarization parameter; and when the polarization parameter is certain, the radiation distribution shows small changes with the change of the initial position. At the same time, it is found that the maximum value of stereo angle radiation per electron unit space occurs at the polarization parameter of 0.7 with the electrons initially located on the z positive semi-axis at a position 30μm from the origin.

The frequency-modulated continuous-wave (FMCW) lidar is widely applied due to its high sensitivity and strong antiinterference capabilities. However, when detecting high-speed moving targets, FMCW lidar encounters range-velocity coupling issue. This paper proposes a method to decouple the target distance and velocity by combining linear frequency modulation with a constant frequency shift. In this approach, the frequency of a single-frequency seed laser is modulated periodically. Each cycle of the frequency modulation signal consists of a sawtooth wave and a DC part. The chirped signal is split into two parts. one part serves as the local oscillator (LO), while the other part passes through a continuously operating frequency shifter and an amplifier, and finally emits to the target. The returned signal from the target beats with the LO to produce a radio frequency signal containing both target range and velocity information. The beat signal frequency of the chirped part comes from both the range induced frequency delay and the Doppler shift, while the target velocity only induces the Doppler frequency shift within the constant frequency duration. Therefore, using the known velocity the target range can be calculated from the beat chirped signal. Thereby, the velocity and the range of the target is decoupled. The simulation and experimental results validate the effectiveness of this method, demonstrating the high measurement resolution and low setup complexity.

We constructed an 852nm Faraday laser using a Faraday anomalous dispersion optical filter (FADOF) of cesium as the frequency-selective element. Utilizing the Faraday effect, under a magnetic field strength of 1000G, the center frequency of the FADOF transmission spectrum is optimized to correspond with the wavelength of the Cs transition by precisely adjusting the temperature of the Cs vapor cell. When the cell temperature is 61℃, the peak transmission frequency of FADOF is the same as the 6S_1/2(F=4)-6P_3/2 transition frequency of cesium atoms. The transmission spectrum of FADOF has a maximum transmittance of 80% and a Doppler-broadened transmittance bandwidth of 2.25GHz. The output wavelength is stabilized at 852.356nm within the transmission frequency region. When the laser diode (LD) current and temperature change from 70 to 150mA and 15 to 30℃, its wavelength fluctuations are within 2pm and 1pm, respectively. In summary, we investigate a Faraday laser based on a FADOF with a specific parameter as the frequency-selective element, whose output wavelength can be automatically traced to the atomic transition. Therefore, the Faraday laser can be widely used due to its excellent robustness to fluctuating diode parameters.

The phased fiber laser array is an important technique for achieving high power and high beam quality laser output. The adaptive fiber-optics collimator (AFOC) is a key element of the phased fiber laser array, which is used to transfer the laser from fiber to free space and precisely control the direction of the outgoing collimating beam. To achieve kilowatt-level and higher power laser output from AFOC, it is necessary to design the collimating lens group to meet the high-power demand and analyze the optical-mechanical-thermal coupling effect of this device. According to the dynamic range of AFOC, a large aperture collimating lens group adapted to large deflection angle is presented in this paper. By using the finite element analysis method, the laser is simplified as the body heat source, and the temperature field and stress field at each lens of the AFOC at 1kW-10kW are simulated, and distribution is Gaussian. The wavefront phase analysis of the outgoing beam shows that the aberrations caused by heat absorption of the optical mirror group are mainly spherical aberrations and defocusing terms. At a laser power level of 6kW, the beam quality factor β of the collimated beam can be reduced from 4.6 to 1.6 by compensating thermal defocusing. This study provides a theoretical basis for the design and optimization of high-power AFOC and offers theoretical support for evaluating their reliability.

There is a heat-affected zone in laser processing that affects the quality of the process. However, laser and tube electrode electrolytic composite processing has no heat-affected zone and no microcracking processing method. This method is subject to plasma breakdown during the machining process, which affects the quality of the machining. A real-time observation platform has been set up for the study of laser transport stability mechanisms in electrolytes. Focusing lens electrolyte breakdown, laser power density, breakdown frequency threshold, etc. were studied for 25mm, 50mm, and 77mm focal lengths, and it was found that breakdown was not easy to occur under the 77mm focusing lens. On the basis of this research on the tube electrode length, laser incidence angle, and other factors affecting the stability of processing, it was found that the laser incidence angle has an impact on the laser energy density distribution, but does not affect the laser focusing center of gravity position, and the increase in the length of the tube electrode helps to improve the laser energy density distribution. Using this processing method, a large depth grating-type workpiece was successfully processed on stainless steel, verifying the stability of the method of laser and tube electrode electrolytic composite processing.

Optical field modulation is one of the common means of improving laser processing results. As a new and high-quality composite laser processing method, waterjet-guided lasers have been less studied in terms of optical field modulation. In order to investigate the feasibility of different energy distributions with different shapes of lasers in the field of waterjet-guided laser processing, the light transmission characteristics of different laser beams in waterjet are investigated using simulation. A three-dimensional waterjet-guided laser transmission model was developed to investigate the differences in energy distribution of a flat-topped beam, a Gaussian beam, and beams of various shapes incident on the waterjet. It is shown that the laser energy in the waterjet is still Gaussian-like after all beams are incident on the waterjet and reached a steady state. The reasons for the formation of the phenomenon are also analyzed based on geometrical optics.

A deformed square microcavity laser, based on internal mode interactions, exhibits spontaneous chaotic behavior without external disturbances. Unlike traditional methods that rely on photodetectors for photoelectric conversion, we propose and demonstrate a novel approach to directly extract chaotic signals from the laser's P-electrode. This scheme successfully extracts the chaotic electrical signal with a 4.4GHz bandwidth. Our approach offers advantages in cost-effectiveness and simplicity. It holds promise for applications such as high-speed physical random number generation and radar detection.

Narrow linewidth pulsed single-frequency fiber laser has the characteristics of excellent coherence and high peak power, and has been widely used in coherent LiDAR, precision measurement and nonlinear frequency conversion. In this work, energy scaling of single-frequency laser with long pulse duration and low repetition rate is demonstrated through leveraging an all-fiber amplifier based on polarization-maintaining (PM) large mode area tapered Yb-doped fiber. With dedicate synchronous pulse pumping for suppressing the inter-pulse ASE effect, and pre-shaping of the seed pulse for compensating the distortion of temporal profile, a 1064nm pulsed single-frequency laser output with an energy of 370mJ is realized with a repetition rate of 100Hz. In addition, the rectangle pulse shape is well maintained with a duration of 1.1ms. It is believed that the obtained result represents the highest energy ever reported for pulsed single-frequency fiber lasers.

With optimized buffer design, we demonstrate a new InAs/AlSb resonant tunneling diode (RTD) on lattice-unmatched semi-insulating (SI) GaAs (100) substrates aiming for terahertz oscillators. To obtain high crystal quality and smooth surface, 5 periods InGaAs/GaAs (2ML/2ML) superlattices (SLs) buffer layer was used as dislocation filters (DFs). Xray diffraction (XRD) measurement showed the full width at half maximum (FWHM) of 331arcsec and surface roughness of 2.4nm over 10μm×10μm. 8-μm-diam diodes were fabricated by standard mesa process. I-V characteristic of the diodes shows negative conductivity at room temperature and a peak current density of 1.79×105A • cm^-2 was achieved.

Carbon fiber reinforced composites (CFRP) have the characteristics of high specific strength, corrosion resistance, and low density, and are widely used in aviation and military fields. Compared with traditional laser processing, the waterjet guided laser has little effect on CFRP thermal injury and has a large depth capability, waterjet guided laser processing has greater application prospects in CFRP. In this paper, high-power waterjet CW lasers at 532nm wavelength were used to cut CFRP. The variation of CFRP cutting depth and cross-section Heat-Affected Zone (HAZ) under different duty cycle and frequency was studied. Confocal laser scanning microscope was used to observe the three-dimensional morphology, cross-sectional thermal influence and fiber damage of the trench. The experimental results showed: The cutting depth and HAZ of CFRP increased with the increased of duty cycle. When the duty cycle increased from 20% to 40% at 10 kHz at 300 W laser power, the cutting depth was increased by 88.7%, and the maximum HAZ of the cross-section was increased by 56.3%; when the frequency increased from 10 kHz to 20 kHz at the 20% duty cycle of the laser power of 300 W, the cutting depth was increased by 11.9%, and the maximum HAZ of the cross-section was decreased by 16.6%. According to the results of CFRP cutting experiment, the duty cycle had a large influence on the cutting depth and the maximum HAZ, while the frequency had little influence on the cutting depth and the maximum HAZ. Large duty cycle could lead to damage to carbon fibers and high frequency lead to an increased in melt. The damage degree of fiber caused by duty cycle was more obvious. This study can provide technical guidance for cutting CFRP with high power waterjet guided CW laser.

Non-line-of-sight (NLOS) target localization technology achieves the localization of hidden targets by detecting and analyzing photons reflected or scattered by objects outside the direct line of sight. This approach has broad application prospects in fields such as autonomous driving and disaster rescue. This paper proposes a photon time-of-flight-based nonconfocal NLOS localization method, which employs a virtual wave algorithm for preliminary imaging of targets in complex scenes. Subsequently, the truncated singular value decomposition (TSVD) optimization method is utilized to extract the main features of the target solution. By reducing the computational time for redundant features and minimizing noise impact, this optimization achieves rapid and high-precision NLOS target localization. The experimental results indicate that the TSVD-optimized NLOS target localization method can accurately locate hidden targets. Within a target movement range of 50cm, the lateral positioning error is within 1cm and the axial positioning error is within 1.5cm, validating the high-precision target localization capability of this method in NLOS detection scenarios.

We propose a 1950nm high average power, large pulse energy narrow-linewidth nanosecond pulse fiber laser. A closed-loop temperature control technique is employed in the design of the seed laser driving circuit system to ensure high power, high wavelength stability, and ultra-low noise characteristics. The acousto-optic modulator (AOM) is used to modulate the pulse of a continuous seed laser, and the rise time of the output pulse can be controlled to obtain the desired pulse shape and width. A master oscillating power amplifier (MOPA) structure is adopted to amplify the modulated power of the laser. Amplified by cascade amplification technique, the average output power of the pulse with the output pulse train has a repetition rate of 10MHz is 3.5W and the pulse width is 300ns, corresponding to a peak power of 1.17kW and a pulse energy of 350μJ. This type of fiber laser has vast possibilities of application especially in lidar and high-precision measurement.

Sealing design is an effective way to prevent pollution of high power laser. The thermal stress and installation distortion of sealed optical window seriously affect the quality of laser beam. Based on the design scheme of glueless welding seal, this paper fully considering the material, absorption rate and welding layer interaction of the optical window and the base, combined with the finite element simulation method, the distortion of the sapphire and fused silica optical window surface caused by temperature drift and the installation stress was calculated. through the optimization and simulation of the V-shaped flexible release form of the installation stress, the physical model of the optimal design is obtained. Then, the temperature field, deformation and refractive index distribution of the optical window assembly is analyzed during the TEM₀₀ mode Gaussian beam lasing process and the effect of optical window surface distortion, defocusing amount and beam quality degradation with lasting time is calculated. At last, the influence of the change of the internal and external pressure difference is calculated. The results show that the leakage rate after welding is better than 10^-12Pa·m³/s, RMS of the mounting surface accuracy is 0.013 λ. The laser power is 10kw and the light lasting time is 120s, the laser beam quality degradation rate β < 1.1, the relax meets the system requirements. The research results provide an important reference for the design, simulation analysis, laser transmission beam quality control and correction of high-power laser anti-pollution and sealed light window components.

Bismuth (Bi)-doped glasses and fibers have been regarded as the most promising gain medium for broadband optical amplifiers. However, the Bi-doped glasses and fibers still meet low gain and insufficient efficiency due to the volatilization, uneven distribution, and uncontrollable valence states of Bi ions in the high-temperature (~2000°C) modified chemical vapor deposition process. Herein, we modified the sol-gel method and synthesized uniform Bi-doped glass with a doping concentration of 0.5wt.% Bi ions at 1300°C. Employing an 808nm LD as a pump, the Bi-doped glass showed a broadband fluorescence with the emission peak at 1413nm and a FWHM of 112nm. On this basis, the Bi-doped fibers were fabricated by rod-in-tube method. The background loss was measured to be 0.27dB/m at 1550nm. A 40m Bi-doped fiber amplifier was constructed by 808nm backward pumping. The maximum on-off gain at 1395nm reached 36dB, heralding the potential of our modified sol-gel method for high-gain Bi-doped glass and fiber fabrication.

Nickel-based superalloys are widely used in aviation, aerospace, energy, petrochemical and other industrial fields due to their excellent high temperature strength, oxidation and corrosion resistance, excellent creep and fatigue resistance. However, there are many problems in the traditional processing methods, such as tool wear, thermal/mechanical damage of materials and so on. These problems limit the processing ability of micro structures and complex surfaces, making it difficult to process nickel-based superalloy components with high quality. Laser processing has the advantages of high precision, non-contact and green, which has become an effective means of nickel-based superalloy surface processing. In this paper, a new process of rotational multi-beam coupled nanosecond laser processing was used to study the groove cutting of nickel-based superalloy with variable defocus amount. The morphology and structure of the groove were observed and analyzed by laser confocal microscope and scanning electron microscope. The results show that the groove width is the smallest and the groove depth is larger when the defocus amount is -1.0mm, and the laser energy density is larger when the defocus amount is close to -1.0mm, and a relatively high adhesion layer is formed between the groove edge and the unmachined surface. By analyzing the groove straightness under different defocus amounts, the groove straightness first decreases and then increases, and the straightness is the smallest at -1.0mm, indicating that -1.0mm defocus position is a relatively suitable processing position. The research work can provide process guidance for the laser processing application of nickel-based superalloys.

Titanium alloys are widely used in aerospace, automobile manufacturing and biomedical fields due to their excellent comprehensive performance. TC4 titanium alloy is a typical difficult-to-machine material due to its poor machinability and machining difficulty. During conventional laser processing of titanium alloys, the oxides generated in the machining area will affect the material removal effect. How to avoid the buildup of oxides is a key issue in the processing of TC4 titanium alloy. This paper investigated the effect of blowing assistance on the laser ablation characteristics of TC4 titanium alloy, and carried out the blowing assistance laser ablation tests. And the laser ablation threshold of TC4 titanium alloy was calculated using the equivalent diameter method. The effect of laser power and blowing assistance on the surface roughness of the edge of the ablated holes and the depth of the holes were explored. The results show that when the repetition frequency is 10kHz, the wavelength is 532nm, and the ablation time is 6s, the laser ablation threshold of TC4 titanium alloy is calculated to be 0.363J/cm², and the surface roughness and hole depth of the ablation hole edges increase with the increase of the laser power or the application of the blowing assistance. Combined with the characteristics of heat transfer and material vaporization in laser ablation, the pulsed laser could be equivalent to a continuous laser, on the basis of which a two-dimensional transient numerical model was established, and the evolution of the surface topography of the workpiece in laser ablation is simulated to predict the trend of the hole depth under different powers. The results show that the average error between the simulation and the experimental results under the three laser powers is 11%. The research work in this paper can provide a reference for the optimization of laser machining process parameters of TC4 titanium alloy.

Silicon carbide ceramics possess excellent properties such as high hardness, wear resistance, high temperature resistance, and corrosion resistance, making them widely used in the aerospace industry. However, due to their high hardness and brittleness, traditional processing methods such as grinding and milling tend to generate surface debris, cracks, and tool wear during the machining of silicon carbide ceramics. Laser processing, as a non-contact processing method, possesses technological advantages. This paper carried out the laser grooving process for silicon carbide ceramics based on ultrasonic vibration assisted rotating beam with nanosecond laser. The effects of single pulse energy and ultrasonic vibration on the depth and width of the micro-groove and the three-dimensional morphology of the deposited layer were investigated. The results show that when the single pulse energy is less than 700μJ, the depth and width of the micro-groove increase with the increase of the laser single pulse energy, and the depth and width of the micro-groove tend to stabilize when the single pulse energy reaches 700μJ. When the ultrasonic frequency is 20kHz, the width of the micro-groove becomes wider with the increase of the ultrasonic amplitude, and the depth of the micro-groove decreases with the increase of the ultrasonic amplitude, this is because the ultrasonic vibration direction is perpendicular to the scanning speed direction, which makes the laser beam interact with the material in a wider area, thus generating an energy dispersion effect. Comparing the conditions with and without ultrasonic assistance, it is found that the thickness of the deposited layer in the micro-groove with the use of ultrasonic vibration processing is smaller than that in the micro-groove without ultrasonic vibration processing, and the thickness of the deposited layer decreases with the increase of the ultrasonic amplitude. Line scanning of the processed area using EDS reveals that ultrasonic vibration can reduce the oxygen content on the micro-groove surface to some extent. This study provides a new process solution for efficient and high-quality laser processing of silicon carbide ceramics.

In a narrow-linewidth fiber laser, temporal stability of the seed is of great significance for suppressing nonlinear effects during the power amplification. Based on a 1050nm narrow linewidth fiber oscillator, spectral and temporal characteristics have been quantitatively analyzed with four different topological structures. Experimental results reveal that adding a ~20m passive fiber between the high reflection grating and gain fiber can significantly improve the temporal stability of the oscillator. At the same power level, the normalized standard deviation has been reduced by ~46.8% and the 3dB spectral linewidth is only broadened by 0.016nm. Further verification of the optimization measures will be conducted in a high-power amplifier in the future.

The excimer laser, with advantages of short wavelength, high energy, and tunable repetition rate, serves as an alternative device for inertial confinement fusion (ICF). However, the current bulky size of excimer lasers presents challenges for engineering implementation, leading to significant engineering difficulties. Modularization of diodes proves to be an effective approach for reducing device volume and engineering complexity. The goal of modularization is to achieve higher efficiency and reliability within a smaller footprint, where numerical calculations of electrostatic fields play a crucial role in realizing these objectives. This paper introduces the applications of electrostatic field numerical calculations in diode insulation structure design, suppression of cathode edge emission effects, and mitigation of electron beam scrapping effects, underscoring the scenarios where excimer laser diodes necessitate the utilization of electrostatic field calculations in their design. The research presented herein can serve as a reference for enhancing the efficiency and reliability of electron-beam-pumped excimer laser diodes.