This PDF file contains the front matter associated with SPIE Proceedings Volume 12792, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In an effort to discuss the evolution process of high-energy electron radiation in circular-polarized intense laser pulse with time in detail, a model describing the interaction between a high-energy single electron and intense laser pulse is built on the basis of Lagrange equation and electron energy equation. It is clearly illustrated how electron radiation evolves over time in space, time and frequency domain. By modulating the interaction time between laser and electron and referring to the spatial distribution image of energy, the maximum value and direction of radiation energy per unit solid angle are obtained. Moreover, the impact of the action duration on the radiation power and frequency distribution in this radiation direction is also fully discussed. The findings indicate that the maximum radiation energy per unit solid angle is expected to occur when laser and electron interaction period reaches around 450 fs, and that the time spectrum and frequency spectrum won’t vary considerably after that. As a result, by modifying the duration of the electron-laser interaction, it is possible to more precisely produce the electron radiation with the desired characteristics for the experiment. This has a specific reference value for choosing parameters in practical application settings, which can significantly save costs and improve efficiency.

Abstract. Laser scanning devices are indispensable for material surface treatment, laser drilling, and laser marking; due to the limited scanning speed, the traditional galvanometer scanning system is increasingly unable to match the high repetition rate laser. The scanning speed of the polygon mirror scanner can reach 1000 m/s. Based on the FPGA (Field Programmable Gate Array) control system, the scanning speed of the polygon mirror scanner can be synchronized with the pulse repetition rate of the nanosecond laser so that after a single scan, there is only one laser pulse injection at each scanning position. This paper mainly studies the processing of titanium alloy templates by high-speed polygon mirror scanner and the influence of laser parameters and scanning parameters on the processing process. The processing depth will be changed by the reasonable adjustment of laser parameters. When the laser power reaches 500 W, the hole diameter can get 112 μm, the depth 156 μm, and the taper tends to be 0.325. There is a geometric relationship between scanning speed, laser pulse repetition rate, and scanning hole spacing, and different functions such as two-dimensional laser marking, laser drilling and laser scribing can be realized according to processing requirements. When the scanning speed of the polygon mirror scanner exceeds 800 m/s, the pulse repetition rate is 500 kHz, the spacing between holes is 1.6 mm, the spacing between lines is 1.6 mm, the overall scanning times are 30 times, and the surface processing of about 4000-hole positions takes only 1.5 seconds. At the end of this paper, a typical application case is presented. There are thousands or even tens of thousands of micro-holes on the surface of titanium alloy templates processed by a high-speed polygon mirror scanner. The template shows a good effect after the deposition of biological coating materials or related drugs and can be actively applied to the healing of traumatic bone tissue.

This paper mainly uses laser technology to study the back slotting of PERC (Passivated Emitter and Rear Cell) solar cells. The high-speed laser scanning device based on the polygon mirror can effectively improve the slotting efficiency of PERC solar cells in current industrial processing. The rotating speed of the polygon mirror is 11400 rpm. The focus lens adopts a long focal length of 420 mm, so the maximum scanning speed can be 1000 m/s, the laser power is 500 W, the pulse repetition rate is 500 kHz, the wavelength is 1064 nm, the pulse width is 120 ns, and the size is 100 mm × 100 mm solar cell is scanned and processed 12 times, the scanning speed is 500 m/s, the surface treatment is about 10201 micro-holes the hole depth is 130 nm, and it only takes 0.8 seconds. The theoretical and experimental research shows that this technology will significantly improve the industrial slotting efficiency of the solar cell. In addition, the passivation layer of PERC solar cells mainly adopt slotting and perforating in industry. The former technology is relatively mature but will lose much passivation film area to increase the carrier recombination rate, and the latter industrial processing efficiency is low. While sintering the back electrode, it is easy to produce a "hole" in the back electrode to increase the series resistance of the solar cell, thus affecting the conversion efficiency of the solar cell itself. In this paper, we use the polygon mirror laser scanning device to slot the back surface of the solar cell. At the same time, we also designed a "back dotted line" slotting of the solar cell. Compared with the straight-line slot, the dotted line slotting increases the solar cell's short circuit current and open circuit voltage. It ultimately improves the photoelectric conversion efficiency by 0.04%.

Using computer numerical simulation technology, we discuss in detail the influence of linearly polarized tightly focused laser intensity on the maximum radiation power and optimal position of electrons, and further study the dynamics and spatial radiation characteristics of electrons at the optimal position corresponding to different laser intensities.Our results demonstrate that the optimal position and maximum radiation power of the electron exhibit linear and exponential dependencies, respectively, on the laser amplitude.The initially stationary electron at the optimal position undergoes oscillatory motion,and then moves in a straight line after interacting with the laser, with an asymmetric trajectory. As the laser intensity increases, The azimuth angle of the maximum power radiation power remains 0°, while the polar angle decreases from 41° to 25°, indicating that it approaches the z-axis. The time when the maximum radiation power occurs is approximately 50.7 fs. Addictionally, We further discuss the evolution characteristics of the time spectra in the direction of maximum power radiation.

In order to explore the impact of different laser systems on the perforation capacity of aluminum alloy plates, a combination of numerical simulation and experimental methods is used under the same average power condition. The distributions of temperature field and molten pool of aluminum alloy plates irradiated by long pulse and continuous laser are obtained. The results show that under the irradiation of continuous laser, a stable temperature field will be formed on the surface of the target, and the perforation time will be longer; Under the irradiation of pulse laser, the surface temperature of the target rapidly increases, resulting in a shorter perforation time. Further analysis shows that under the action of continuous laser, the surface heat of targets has sufficient time to diffuse to the surrounding areas through thermal conduction and convective heat transfer, reducing the energy utilization.

To study the effect of laser intensity on the radiation of electron, a model of the interaction between a single electron and a laser is constructed based on Thomson scattering theory. The numerical simulation results show that the oscillatory motion of electron is more intense under the effect of more intense lasers. Meanwhile, the maximum radiated power of electron is increased dramatically, and the direction of maximum radiation is closer to the longitudinal direction. In the direction of maximum radiation, the unit angular radiated power shows an asymmetric bimodal structure in the time domain. When the laser intensity is increased, the symmetry of the bimodal structure is decreased significantly. The results in this paper contribute to the study of nonlinear radiation of electron in strong laser fields.

Piezoelectric ultrasonic transducers are difficult to meet the requirements of high sensitivity and small size for photoacoustic endoscopy imaging. Fabry-Pérot (F-P) resonator ultrasound sensors based optical fiber are not only small in size and high in sensitivity but also easy to integrate with photoacoustic endoscopy imaging systems. However, the typical F-P resonator lacks lateral confinement of the beam and is very sensitive to misalignment, resulting in a significant reduction in the quality factor (Q-factor). We propose a waveguide plane-concave F-P resonator, where the concave structure can provide lateral confinement and solve unaligned, and the waveguide can provide lateral confinement and relax curvature matching between the concave surface and the wavefront. Suitable waveguide length and concave curvature can yield high quality factors (> 10⁴) and Noise Equivalent Power (NEP) low as 29.4 𝑚𝑃𝑎√𝐻𝑧. The structure is directly fabricated on the fiber end face by two-photon polymerization 3D printing technology, the processing accuracy can low as 200 nm. It can accurately and quickly realize complicated 3D structure. And different materials with different characteristics can meet different ultrasonic detection bandwidth and sensitivity.

Nonlinear inverse Thomson scattering (NITS) has gained many applications as premium x-ray sources, and is of great research values. Based on the classical theory of NITS, the effects of laser’s initial phase on NITS radiation are analyzed through numerical simulation when the relativistic electron collides with a circularly polarized ultrashort intense laser pulse. When pulse width of the laser is very short, the initial phase has a significant impact on the symmetry of electron’ trajectory and spatial radiation power, and the electrons’ trajectories show a ‘triple symmetry’ property with respect to the initial phase. The angular distribution of NITS radiation energy is generally circular, but there is a prominent single peak, which shows the high collimation. The direction and energy of the radiation peak can be modulated by initial phase periodically. Furthermore, the symmetry of radiate spatial spectrum varies with the change of initial phase, but the distribution pattern of the spectrum remains unchanged. Broad-band x-rays with different wavelength widths can be obtained at different positions in space. The findings above show that it is feasible to use initial phase of the laser to modulate the symmetry of the x-rays generated by NITS, which also provides a numerical basis for obtaining x-rays with different wavelength widths in practical experiments.

Based on the classical Thomson scattering theory, we theoretically study the electron trajectory and spectrum generated during the frontal collision of electrons with a tightly focused circularly polarized laser pulse. The results show that there is a linear relationship between the initial z-axis coordinate z₀ of the electron and the collision center. The increase in the initial energy and the initial z-axis coordinate of the electron will cause the concentration of the longitudinal motion of the electron and the redshift of the spectrum. The difference between the two is that the higher the initial energy of the electron, the smaller the transverse motion of the electron, and the higher the maximum single harmonic energy of the spectrum, while the increase in the initial z-axis coordinate of the electron will cause the interference fringes of the spectrum to increase first and then decrease, and the maximum single harmonic energy will decrease overall, with a jump point at z₀ = 15λ₀.

Based on the classical Thomson scattering theory, a model of the interaction between a single electron and a periodic order linearly polarized Gaussian laser pulse is constructed and simulated by MATLAB. The effect of the initial phase on the distribution of space energy radiation is studied. The results show that the distribution characteristics of electron motion and energy radiation show spatial asymmetry with respect to the initial phase under the condition of non-tightly focused pulse. Specifically, the transverse motion and energy radiation distribution of electron are affected by the initial phase, resulting in a longitudinal drift. The spatial distribution of energy radiation shows obvious spatial asymmetry with respect to the initial phase, and its energy asymmetry coefficients are periodic symmetric with respect to the initial phase, and the reciprocal transformation relationship with π interval is presented. Then, we explored the influence of the laser pulse width and the initial phase on the asymmetry coefficient of the radiation energy and found that the distribution of the asymmetry coefficient on the initial phase of the radiation changes continuously clockwise with the increase of the laser pulse width.

Based on the single-electron model, the spatial, temporal and spectral emission characteristics of the radiation generated by the electron oscillation driven by a circularly polarized pulse of laser with a FWHM (Full Width at Half Maximum) of 20 femtoseconds and a light intensity at 10²⁰W/cm² are investigated by theoretical analysis and numerical studies. Electron moves in highly relativistic motion which make it generates an ultrashort radiation about 2.5 attosecond. The numerical results show that the spatial, temporal and spectral distributions in detail of the radiation are sensitively dependent on radiation directions which is neglected by Lee et al. We study a kind of spectral modulation process which has practical significance.

A triple-wavelength erbium-doped fiber laser based on seven-core fiber (SCF) interferometer is proposed and successfully implemented. In the structure of the laser, a special structure of single-seven-single core is used to realize laser interference, which is composed of a 6 cm SCF and ordinary fiber optic patch cables fused by convex cone. In the laser with simple structure, triple-wavelength output with central wavelengths of 1530 nm, 1544 nm and 1558 nm are obtained by adjusting the polarization controller, and the optical signal-to-noise ratio (OSNR) of the triple-wavelengths is approximately 60 dB. The laser has high stability in terms of both wavelength and power. In the stability test of 150 min, the frequency drift of three wavelengths is approximately 0.4 nm, and the output wavelength peak power jitter is approximately 1.6 dB. The laser has the characteristics of simple structure and high stability, and has broad application prospects in the fields of optical fiber sensing, wavelength division multiplexing (WDM) optical communication system and microwave photonics.

Traditional optical imaging techniques are limited in terms of information acquisition and processing methods, as they can only image targets within the line of sight. Non-Line-of-Sight Imaging (NLOS) aims to enable imaging beyond the line of sight. One important method in NLOS imaging is based on the measurement of photon time-of-flight. It involves analyzing the paths of light propagation before reaching the detector to reconstruct the surface of hidden objects. In non-line-of-sight scenarios, light from non-line-of-sight objects can be imaged after being reflected by visible objects in the scene. However, the multiple reflected light signals in traditional imaging are typically considered as noise due to their low intensity. In contrast, non-line-of-sight imaging captures the weak and scattered light signals that have undergone multiple reflections, and uses the time of photon arrival to infer the shape of objects hidden from the line of sight. This paper explores the relationship between the shape of hidden object surfaces and the sensed light signals under multiple bounces. A model is constructed to recover the three-dimensional shape from diffuse reflections and infer the shape of objects outside the line of sight. The reconstructed model and method are validated using a dataset collected from real-world scenarios.

Ultraviolet (UV)-mediated inactivation has been widely used in various fields. The doses needed for inactivation of various pathogenic bacteria were compared, and the bacterial survival state after sterilization was determined. The effective sterilization methods and effect of UV irradiation on DNA structure were explored. In the experiment, a UV-C lamp device with multi irradiance and regular irradiation was designed and assembled for irradiation of bacteria. A variety of bacteria were used under unified culture environment and irradiation conditions, and the sterilization rate was calculated through the proliferation of bacteria after UV irradiation. The irradiation dose and dose curve of each strain to achieve the bactericidal rate were determined. The penetration of UV radiation into bacteria was evaluated through the killing effect of UV radiation on colonies. The differences among bacteria and UV energy amounts is discussed herein, and the influence of irradiance on the inactivation effect was demonstrated. Irradiance and irradiation dose play a decisive role in the efficacy of UV sterilization. The UV dose was positively correlated with the bactericidal rate; the bactericidal rate increased with increasing dose. High-dose UV irradiation could kill multilayer bacteria. Detection of bacterial damage showed that the UV energy in the experiment did not break the DNA fragments to yield small-molecular bands. The ultramicrostructure diagram showed that UV irradiation caused condensation of the linear DNA, and the abnormal DNA structure could not replicate or be inherited. The application of UV sterilization requires a suitable energy range.

In this paper, the Thomson scattering interacting with periodic magnitude laser pulse is studied numerically and theoretically based on classical radiant theory. By using MATLAB simulation, we find that radiant energy spectrum of electron proves that relativistic electron colliding with the periodic magnitude pulse of laser can obtain the narrow second ray pulse. The implications of original carrier envelope phase of incident periodic scale pulse of laser on spatial radiant characteristics, temporal spectral characteristics and spectral characteristics of Thomson scattering radiant of electrons under periodic scale pulse of laser are investigated. Results prove that radiant accumulates in an area of the cone centered in backward radiant direction and that each radiant power is optimal in backward direction. It is also found that single-period pulse of laser scattering with a fixed original carrier envelope phase shift can produce a single oblique second pulse. As incident pulse of laser is close to a single period pulse, the emission spectra of electrons indicate a radiant pulse duration of oblique seconds of x-rays. In addition, implication of original carrier envelope phase on radiant spectrum is equally significant for the high and low frequencies of spectrum, has no implication on central part of spectrum. From the above conclusions, we can conclude that implication of original carrier envelope phase on energy spectrum makes radiant very relevant for characterizing pulse of laser of periodic magnitude or for determining degree of synchronization between electrons and pulse of laser.

Using the single electron model, the effects of pulse width on the relativistic motion and radiation characteristics of electronic oscillation generated by linearly polarized intense femtosecond laser pulses are studied theoretically and numerically. For short period laser pulses, the electron trajectory exhibits an asymmetric serrated pattern, while for multi period laser pulses, it is not similar to a doubly symmetric serrated pattern. It is found that for a short pulse width, the full space distribution mode of electron emission is banana shaped, while for a long pulse width laser pulse, the Radiant flux per unit Solid angle is rabbit ear shaped, pointing to the propagation direction of the laser pulse, with narrow divergence.

In this paper, we derive analytical formulas for the coherence length of a spherical wave propagating in oceanic turbulence based on the theory of second moments and power spectrum of homogeneous isotropic oceanic water. By equating the spherical wave coherence length solutions in oceanic and atmospheric turbulence, we express oceanic turbulence parameters using an equivalent structure constant employed in turbulent atmosphere. Our results provide a convenient analytical and numerical tool for analyzing beam propagation problems in oceanic turbulence and improve the theoretical basis for applications.

Based on the classical Thomson scattering theory, a model for the interaction of a single electron with a linearly polarized laser pulse is constructed and numerically simulated to investigate the relativistic motion as well as the full-space characteristics of the electron radiation, which is driven by a linearly polarized femtosecond laser pulse theoretically and numerically. In the process of the study, it is found that the radiation’s full spatial distribution indicates different characteristics at different intensities. At low laser intensities, the radiation spatial spectrum is the same as that of a dipole antenna. As the laser intensity increases, the spatial spectrum changes from fourfold rotational symmetry to twofold rotational symmetry, and the radiation direction becomes more and more inclined to the Z-axis, i.e., the collimation becomes better. These phenomena are mainly influenced by the electron dynamics and the nature of the linearly polarized femtosecond laser pulses. In addition, as the laser pulse intensity increases, the maximum radiation angle decreases and the maximum radiation power increases. The above-mentioned laws allow us to measure the intensity of the experimentally linearly polarized laser pulses in reverse, based on the observed radiation properties.

We demonstrate an ultra-fine fiber optic hydrophone array for acoustic detection. It is consisted of Weak Reflection Fiber Bragg Grating (WFBG), including four layers: optical fiber layer, coating layer, tensile layer, and sealing layer. Moreover, an hydroacoustic detection system which based on matched interference is established. The responses of underwater acoustic signals, generated by vibration liquid column, in the areas of amplitude, phase and frequency were demodulated simultaneously using the combining algorithm of digital arc tangent and PGC algorithm. A relative flatness response of 3dB was achieved in the frequency range from 200 to 2000 Hz. And the experiments showed that acoustic pressure sensitivity is about -147.96 dB (re 1rad/μPa).

As a high reflectivity mirror high refractive index contrast grating has been applicated on many traditional devices in recent years. Instead of the repetition of hundreds alternately stacked high and low refractive index materials, high contrast grating based reflect mirror can achieve near 100% reflectivity only use 1-3 dielectric materials with relatively large refractive index difference. By varying the grating thickness, period or duty circle the reflectivity characteristics of high refractive index contrast gratings can be adjusted. This article discussed the influence of high refractive index contrast gratings on the design of high power vertical external cavity surface emitting lasers. By comparing the effects of grating thickness, period, and duty cycle of the GaAs grating under different polarization conditions, more than 95% reflectivity of both TE and TM polarization can be achieved near emitting wavelength of 1064nm. The heat dissipation of the vertical external cavity surface emitting laser using multi-layer distributed Bragg reflector and high refractive index contrast grating are also analyzed using finite element method. The feasibility of using high refractive index contrast grating in vertical external cavity surface emitting lasers is theoretically analyzed in this article.

The propagation properties of Helical Ince-Gaussian (HIG) beams in oceanic turbulence are analyzed using the random phase screen method. A comparative analysis of the spot centroid wander and the scintillation indices of different order HIG modes as a function of propagation distance has been performed. A comparative analysis of the spot centroid wander and the scintillation indices of different order HIG modes as a function of propagation distance has been performed. The results indicate that compared to the LG_0,1 mode, the HIG mode with order p=m⪆1 has a smaller standard deviation of spot centroid wander and scintillation index during propagation. Especially, the standard deviation of the spot centroid wander decreases with the increase of the HIG mode’s order, while the scintillation indices of odd-order HIG_m,m beams are generally higher than those of even-order HIG_m,m modes. In addition, the scintillation index of the odd-order HIG_m,m beam decreases with the increase of the ellipticity parameter, while that of the even-order HIG_m,m beam increases. Finally, we conclude that under the influence of oceanic turbulence, the HIG mode has a lower scintillation index than the IG mode at the same propagation distance. The results have significant implications for the oceanic applications of the HIG modes.

To achieve efficient optical communication and optical interconnection, it is necessary to develop and prepare detectors with high gain, low noise, high bandwidth and strong anti-electromagnetic interference. Because III-V materials cannot be integrated with CMOS process line, therefore, avalanche photodiodes (APDs) based on germanium silicon substrates are considered as detectors with large scale integration. Waveguide integrated structure can solve the contradiction between response and bandwidth in surface illuminated structure. Moreover, with germanium as the absorption region, a SACM (separate absorption charge multiplication) structure with silicon as a multiplication region has become a widely used device structure. In this work, a new vertical structure waveguide integrated structure of silicon-based germanium APD is designed with the charge layer on both sides of the germanium absorption layer, and the influence of the thickness of the multiplication layer on the dark current is simulated and tested. It shows that when the width of the multiplication layer increases, the breakdown voltage of the device increases, indicating that the electric field level of the multiplication region is similar to that of different devices at the breakdown voltage, furthermore, the simulation and experimental results are basically consistent. Under the input power of -16.8 dBm for 1310 nm incident light, the bandwidth of the designed vertical structure SACM silicon-based germanium APD can reach 25.7 GHz at 15.7 V bias. The primary responsivity of the device is up to 0.68 A/Wand the gain bandwidth product is up to 247 GHz, showing the great potential of the present Ge/Si APD for the application in future high-speed data transmission systems.

Metasurface plays an increasing crucial role in photonics applications due to its powerful control of optical fields, multifunctionality, as well as miniaturization. Metasurface holography, as one promising approach of holographic display, has broad prospects in the fields of color display, 3D imaging, Augmented Reality (AR), and Virtual Reality (VR). However, the reported metasurfaces still suffer from problems such as low transmission efficiency and poor imaging quality in the visible wavelengths, giving rise to extremely challenging to further enhance the efficiency of color holographic imaging. To overcome the low efficiency of reported metasurface holograms, we proposed a metasurface unit structure with high polarization conversion efficiency based on reverse design algorithm, and applied it to color holography. By using the particle swarm optimization algorithm and three-dimensional Finite- Difference Time-Domain (FDTD) method, the structural parameters of a single periodic unit on the metasurface were optimized to achieve effective separation of cross-polarized and co-polarized reflected beams in space, resulting in highly efficient, broadband, and stable polarization conversion. The results indicate that, the average efficiency of circular polarization conversion can reach 93% in a wide wavelength range of 480 to approximately 622 nm when the average reflectance of the cross-polarized component circularly polarized exceeds 80%. On this basis, we further demonstrated the application of the metasurface designed by reverse design algorithm to efficient color holographic imaging. We expect that this broadband and efficient metasurface will accelerate the development of metasurfaces for AR and VR.

Based on the classical Thomson scattering theory, a model of the interaction between a single electron and a circularly polarized Gaussian laser pulse is constructed and simulated by MATLAB. We simulated the trajectory of electron motion - longitudinal velocity of electron motion - radiation space state - radiation spectrum map. The results of the study show that the trajectory of electron motion, the position of the collision center and the distribution characteristics of energy radiation are influenced by the change of pulse width. Specifically, an increase in pulse width leads to a leftward shift in the position of the collision center and a gradual decrease in the maximum amplitude of electron motion. In contrast, the maximum radiation energy increases with the pulse width, in which the red-shift phenomenon gradually weakens with the pulse width, and the originally shifted peak of the strongest radiation energy gradually returns to the θ=180° direction, which means that the collimation of radiation is strengthened. We also studied the radiation state and found that the spatial state of the radiation gradually changes from open black hole-like to needle-like as the pulse width increases, a phenomenon that also indicates that the collimation of the radiation becomes better.

When extended target related Hartmann high-precision wavefront detection is applied to near-ground target imaging, short-range laser transmission and other fields, affected by skylight background, atmospheric turbulence intensity, detector noise and other factors, the subaperture image of correlated Hartmann wavefront sensor is often partially missing, resulting in reduced detection accuracy. In order to analyze the problem of precision degradation, a simulation model of extended target wavefront detection based on correlation Hartman is established in this paper. The model is based on Fresnel diffraction, the working principle of Shake-Hartmann wavefront sensor and the Zernike wavefront reconstruction method. The effects of missing sub-aperture images at different positions and different missing degrees on the accuracy of wavefront reconstruction are analyzed. The relationship curves of RMS and PV values of wavefront reconstruction residuals with image deletion of sub-aperture at different positions and different deletion degrees are obtained by simulation. The results show that different position subapertures and different degree of loss will affect the expansion degree of target in the Hartman subaperture. When the correlation algorithm restructures the wavefront, the impact of the loss of the center subaperture on the wavefront reconstruction accuracy is greater than that of the edge subaperture, and the greater the loss degree, the lower the wavefront reconstruction accuracy.

SiC ceramics have excellent physical and chemical properties, and have been extensively researched and used in electronics, optics, semiconductor and other fields. However, due to its high strength, high hardness and other characteristics, the conventional processing of SiC ceramics faces a series of challenges. Laser processing has become an effective processing technology due to its unique advantages. In this paper, the single pulse ablation tests of SiC ceramic with different powers were performed by using infrared femtosecond laser. The single pulse ablation threshold of SiC ceramic was calculated by using equivalent diameter method and equivalent area method, and the influence of laser power on the depth of the ablation hole was discussed. The results show that when the repetition frequency is 25kHz and the wavelength is 1035nm, the laser ablation values calculated by the equivalent diameter method and the equivalent area method are 0.3454 J/cm2 and 0.3268 J/cm2, respectively. Within a certain laser power range or reaching a certain ablation hole depth, the ablation hole depth augments with the increment of laser power. Beyond a specified laser power range, the hole depth decreases with the increment of laser power due to the effect of plasma shielding and recasting layer.

Micro/nano-structured amorphous carbon promises functional prospects in energy-saving, water purification, nonlinear optics, catalysis, sensors, and the internet of things, but there exist many challenges, especially in rapid synthesized nanostructured carbon materials towards performance improvement. Thereby, a transfer-free digital photochemical synthesis method is studied here via scalable single-step nanosecond laser processing. Controllable photon energy from a 1064nm wavelength nanosecond laser drives different degrees of carbonization on paper surfaces. The blended cellulose-lignin network is converted into a series of micro/nano-stacked porous carbon materials during fabrication. High-resolution transmission electron microscope showcases that lattice characteristics of synthesized carbon shift according to optical parameters. A comparison of material morphologies formed at different conditions can be found here. Nanosecond laser processing opens a new avenue for the rapid preparation of carbon nanomaterials on paper substrates with special textures and special microstructures, promising more carbon-based multifunctional devices.

We have developed a high-power, high-reliability single-mode 980nm semiconductor laser pump module for all-optical networks in the optical communication industry, including terrestrial long-distance optical fiber communication, submarine optical cables, and satellite communication. This module serves as the core key component of Erbium-Doped Fiber Amplifiers (EDFA). To achieve an 80% coupling efficiency, we utilized the 14-pin butterfly device packaging process, coupling our self-developed single-mode 980nm semiconductor laser chip with a specially designed wedge lens fiber. Fiber Bragg grating, and thermal management technology were employed to ensure stable lock wave performance within a temperature range of -40 to 75°C, and a working current of 900 to 1800 mA. The spectral width is <0.5nm, the side-mode rejection ratio exceeds 25 dB, and the in-band power ratio surpasses 95%. The module delivers a single-mode output power exceeding 1.3 W and exhibits a low power stability of no more than 3.5% at a low power of 30 mW. The module features high single-mode output power, low power stability, narrow spectral width, and high edge-mode rejection ratio. After 2000 hours of high-current aging test and reliability verification, all module samples still maintain stable output power, and passed the verification of Telcordia GR-468-CORE. The successful development of this product fills the gap in the field of high-power single-mode 980nm semiconductor laser pump modules in China. It is expected to play an important role in the fields of optical communication systems, laser sensing and scientific research applications.

Structured Illumination Microscopy (SIM) has been widely applied in the biomedical field due to its high imaging resolution and low phototoxicity. However, SIM often requires the acquisition of 9 raw images for reconstruction, which sacrifices temporal resolution. With the emergence of Compressed Sensing (CS) technology, data compression during the sampling process has accelerated imaging speed. By combining SIM and CS techniques, it is possible to further enhance the imaging speed of SIM. In this paper, we propose an algorithm based on the aforementioned concept: utilizing the physical model of CS-SIM, we simulate the generation of a pre-training dataset. Subsequently, we train a deep learning network, namely Nonlinear Activation Free Network (NAFNet), to perform ultrafast and super-resolution reconstruction. This end-to-end approach reduces the complexity of imaging, improves imaging efficiency, and significantly enhances the quality of the reconstructed images. Now, we have achieved a compression ratio of 9:1. Furthermore, the simulated data we utilized in the training process has been generalized. Despite the limited availability of biological samples, we are still able to achieve super-resolution reconstruction of biological tissues.

Silicon carbide fiber reinforced silicon carbide ceramic matrix composites (CMC-SiC_f/SiC) have been widely used in aerospace and other fields due to their excellent properties such as high hardness, oxidation resistance and high temperature resistance. Different from the traditional machining methods, laser processing technology has great application prospects in CMC-SiC_f/SiC. In this paper, the single-pulse ablation test and multi-pulse cumulative ablation test of CMC-SiC_f/SiC were carried out by femtosecond laser at different powers with a wavelength of 1035 nm. A series of experiments were designed to process the ablation pits on the material surface. The diameter of the ablation pits was observed by laser confocal microscope. The variations of the ablation threshold of CMC-SiC_f/SiC surface under different pulse energies and pulse numbers were studied. The results show that the multi-pulse ablation threshold of CMC-SiC_f/SiC decreases with the increase of pulse number, and there is a significant cumulative effect. The multi-pulse ablation threshold of CMC-SiC_f/SiC is mainly related to the number of pulses, which is determined by two parameters: accumulation factor and single-pulse ablation threshold. The single-pulse ablation threshold of CMC-SiC_f/SiC is 1.1914 J/cm², and the accumulation factor is 0.6245. In femtosecond laser processing, the pulse accumulation effect has a significant influence on the ablation of hard and brittle material CMC-SiC_f/SiC. This study can provide technical guidance for process optimization.

Vortex optical field is widely used in optical communication, particle control, quantum information and other fields due to its special physical structure. Coherence is an important inherent property of the beam, with unique advantages in resistance to speckle noise and atmospheric turbulence disturbance. In this paper, taking the cosine-Gaussian correlation function as an typical example, a mathematical model of the cosine-Gaussian-correlated Schell model vortex (CGCSMV) source is established. Using the extended Huygens-Fresnel integral, and the generalized anisotropic turbulence spectral model, we derive an analytical expression for the far-field cross spectral density function of a CGCSMV beam propagating in anisotropic turbulence. Lastly, we perform numerical simulations of the behaviors of the far-field spectrum of our beam. The results of this paper have some practical reference value for the new optical field regulation, optical communication and lidar system.

With the development of biomedicine, biomedical metal materials have been widely concerned because of their good toughness and reliability. AISI 316L As the main stainless steel implant material, it is widely used in fracture fixation and joint replacement objects. However, the surface of 316L has low hardness and poor wear resistance. Electrical assisted laser shock reinforcement can first power the material, and then laser shock reinforcement, which produces electric effect, joule thermal effect can improve the material performance and improve the surface hardness. In this article, pre-impact (Laser Shock Processing After Applying Electro-pulsing, LSP-AAE) with single impact reinforcement (Laser Shock Processing, LSP) of 316L stainless steel, and studying the micro-hardness, surface morphology and friction and wear characteristics after treatment, it is found that the micro-hardness improvement effect of the electro-assisted laser shock enhancement 316L is better than the single laser impact enhancement, The LSP samples and the LSP-AAE samples increased by 25.2% and 30.2%, respectively, when compared with the original samples. Using GF-I high temperature reciprocating friction wear test machine on the original sample, LSP sample and LSP-AAE sample for friction wear experiments, analyze the difference of friction coefficient and wear rate of the three samples, it is found that under the same frictional conditions, the mean friction coefficient of the original, LSP, and LSP-AAE samples were 0.48, 0.40, and 0.36, respectively. The wear rates were 5.18×10^-6, 4.76×10^-6, 4.25×10^-6 mm³s^-1 N-1. Both the reduced friction coefficient and the wear rate, LSP-AAE treatment improves 316L stainless steel wear resistance more than a single laser impact reinforcement.

Perfect vortex beam is a light field whose radial profile is independent of Orbital Angular Momentum (OAM). This new kind of optical vortex beams has unique advantages not only in the field of fiber coupling, optical trapping and tweezing but also in free space optical communication. This work provides a simulation method to analyze the mode purity evolution of perfect vortex beams in turbulent media, aiming to present an insight to the influence on the superposition types of multimode light fields. It is found that the anti-disturbance ability of multimode perfect vortex is better than that of single mode under certain conditions. Incoherent superposition leads to a stronger turbulence resistance and a more stable output compared to those of coherent superposition. The results of this paper can be useful in the fields of free space optical communication.

Pressure monitoring has an important significance in fields such as petrochemical, energy, and power engineering. Compared to electronic pressure sensors, fiber optic grating pressure sensors have the advantages of small size, simple structure, and anti-electromagnetic interference. This paper proposes a polymer encapsulated fiber Bragg grating (FBG) dynamic pressure sensor and uses a semiconductor optical amplifier (SOA) - fiber ring laser (FRL) and an array waveguide grating (AWG) demodulator to form a fiber Bragg grating dynamic pressure sensing demodulation system. The experimental results show that the laser output of the SOA-FRL system is stable; in the fiber Bragg grating pressure test, the pressure sensitivity of the dynamic pressure sensor based on SOA-FRL can reach -33.17 pm/MPa at two pressure environments of 1~ 20 MPa and 0.1~0.8 MPa. The temperature dependence test shows that the sensitivity of the dynamic pressure sensor is 8.14 pm/℃ in the temperature range of 23 ~ 60℃. The temperature sensitivity of the dynamic pressure sensor is slightly lower than that of the reference FBG sensor (9.79 pm/℃). In addition, the effects of different sensitizing materials on the sensitivity of the pressure sensor are compared. The results show that the sensitivity of polymer materials is higher than that of metal materials. Because the proposed dynamic pressure sensor system based on fiber ring laser and array waveguide grating demodulator has the characteristics of high sensitivity, simple structure, and the demodulation of dynamic signals, it has a promising application prospect in oil exploitation, transportation, structural monitoring and other fields.

Bidirectional Oscillating-Amplifying Integrated Fiber Lasers (B-OAIFL) combine the advantages of Oscillating-Amplifying Integrated Fiber Lasers (OAIFL) and bidirectional output fiber lasers, including high efficiency, simple control logic, good anti-back reflection, low cost, and small volume. In this work, we introduced the (2+1)×1 Side Pump Signal Combiner (SPSC) between the Output Coupler Fiber Bragg Grating (OC-FBG) and the amplifying sections to address the temporal instability of the laser at low power levels under the counter pumping. Two groups of wavelength-stabilized 976 nm Laser Diodes (LDs) were directly coupled into the oscillating section to increase the laser power within the cavity, and then, a 60 W-level time-stabilized threshold signed as photodetector-detected no-pulse characteristics was achieved. We compared the output characteristics with two different fiber-coiling structures in the oscillating section (STR1, STR2). STR1 was coiled in a single-track-shaped fiber groove with a diameter ranging from 8.0 cm to 10.7 cm, while the coiling diameters of the two output ports were different. For STR2, an '8'-shaped coiling was adopted with gradually varying diameters from 8.0 cm to 9.5 cm and the same coiling diameter of 8.0 cm at both ports. The Transverse Mode Instability (TMI) threshold under the unidirectional pumping at end A and end B were 2271 W and 2530 W, respectively, with Structure one. With Structure two, the thresholds at end A and end B were 2735 W and 2508 W, respectively. Based on STR2 under the bidirectional pumping with a total pump power of 6997 W, we finally achieved a laser output of 2655 W at the end A and 2491 W at the end B, with a total power of 5146 W and a good beam quality of M² to approximately 1.32 at end A and M² to approximately 1.45 at end B, respectively. The Stimulated Raman Scattering (SRS) suppression ratio exceeded 40 dB for both end A and end B.

Laser metal deposition (LMD) is an additive manufacturing technique that utilizes powder as its material. The powder is transported through the nozzle coaxially, where it converges with the laser beam onto the surface of the substrate. With the assistance of auxiliary gas, the powder melts upon laser irradiation and is deposited layer by layer onto the substrate, forming the desired component. Real-time monitoring of the deposition height plays a crucial role in enhancing the precision of LMD, reducing defects such as edge collapse and surface unevenness. It represents one of the fundamental aspects in achieving high-quality metal additive manufacturing. In this study, a laser metal deposition height prediction method based on a multi-modal neural network was proposed. The network architecture consisted of a convolutional neural network (CNN) and a fully connected network (FCN). The CNN extracted and analyzed the characteristics of the molten pool, generating a feature vector. This feature vector, along with the molten pool temperature, was fused as input into the FCN, ultimately predicting the deposited height. Compared with the predicted results of support vector regression (SVR), multi-modal neural networks can quickly predict the deposited height and track their changing trends. The model achieves a remarkable prediction accuracy of 95% and exhibits robustness in handling outlier values. The proposed network framework holds considerable potential in facilitating real-time control and fine-tuning of the laser metal deposition process.

Refractory metal tungsten (W) has a very high melting point (3420℃) and excellent high temperature mechanical properties, and has great prospects for application in aerospace, nuclear industry and other defense fields. Due to the high melting point and high thermal conductivity of pure tungsten, high power is required to melt it, while tungsten has a high ductile-brittle transition temperature (DBTT) and a low room temperature brittleness. These two aspects make it impossible to avoid porosity or cracking during machining, limiting its further application. So more effective tools are needed. The ultrafast laser can reach high peak power due to its extremely short pulse width. Adjusting the frequency can achieve heat accumulation in the heated region. These two effects make it possible to process materials with high melting points without having to increase the power all the time. The ultra-fast laser excessively high peak power can lead to cold processing of the material for removal, so figuring out the right process parameters is especially important. Femtosecond laser additive manufacturing of pure tungsten has been previously documented and compared with parts made using different pulse widths and CW lasers, showing that fully dense tungsten parts with finer grain size and increased hardness were obtained. By further reducing the pulse width at 200 fs, we achieved printing of pure tungsten at higher densities. Hardness tests demonstrated the superior performance of the printed samples compared to those made by conventional casting, continuous wave laser and 800 fs laser-selective melting, and this study is expected to promote the wide application of narrow pulse width lasers in laser additive manufacturing.

There have been many studies on the forming process of CoCrFeNi high-entropy alloy by laser additive manufacturing, but there is a lack of systematic research on the numerical simulation of the forming process. This paper establishes a three-dimensional transient model of laser additive manufacturing high-entropy alloy by combining numerical simulation with experiment. The temperature field distribution of laser additive manufacturing CoCrFeNi high-entropy alloy on 316L substrate is simulated. The temperature distribution cloud diagram is obtained under different laser process parameters and the temperature change curve at the same node. The mechanism of surface spheroidization, pore, and metallurgical defect formation is revealed, and the experimental verification is realized. Finally, the forming process of laser cladding CoCrFeNi high entropy alloy block was explored. The results show that the maximum temperature of the cladding layer can reach more than 5000 °C during the cladding process. When other conditions remain unchanged, when the laser power increases from 1000 W to 1400 W, the temperature at the junction increases from 1588.63 °C to 2238.64 °C. At the same time, due to the insufficient melting of metal powder and the impact of powder on the molten pool, the surface of the additive is powdered and spheroidized. In addition, low laser power and low scanning speed will cause metallurgical defects between the cladding and the substrate.

A tunable multi-wavelength Brillouin–erbium random fiber laser with a half-open cavity is proposed and experimentally demonstrated. In this simple laser device, stabilized 15-order Stokes lines and 3-order anti-Stokes lines can be obtained by adjusting the pumping power. By adjusting the wavelength of Brillouin pump, the random laser wavelength tuning is realized, which can be tuned to 1550.5 nm-1565.5 nm. In addition, the laser has high wavelength and power stability. The wavelength fluctuation range of 1–10 orders Stokes light is less than 0.01 nm, and the corresponding peak power fluctuation is less than 1.8 dB. The results show that the laser has the advantages of simple structure, many spectral line orders, wide tunable wavelength range and high stability, which makes it have broad application prospects in many fields, such as fiber sensing, microwave photonics, optical imaging, optical communication systems, precision metrology and so on.

Low-time jitter optical pulses are widely used in precision ranging, photonic microwave generation, optical frequency comb generation, and photonic sampling. In order to obtain highly stable optical pulses at 1560 nm with an ultra-high pulse frequency of approximately 10GHz, a self-regeneratively ultrafast mode-locked laser with a polarization-maintaining fiber cavity is demonstrated in this paper. The laser adopts a section of polarization-maintaining erbium-doped fiber as the gain medium, a lithium niobate phase modulator as the active modulation device, and the rest of the resonant cavity are composed of passive polarization-maintaining fibers. This results in a total ring cavity length of about 10.7 m. The ring cavity can stimulate multiple longitudinal modes under free running conditions. One of these longitudinal mode frequencies is selected through using a self-built clock extraction and recovery module to generate RF signal with a frequency of 10 GHz. The amplified RF signal at 10 GHz drives the phase modulator and modulates the optical field in the cavity, which results in a stable self-regeneratively mode-locked pulse in the entire laser loop. It quickly achieves a stable ultrafast mode-locked state with a low timing jitter without any external RF reference. A pulse frequency of 10.0076 GHz and a pulse width of 3.14 ps were obtained, together with a side-mode suppression ratio of more than 80 dB and a phase noise of about -110 dBc/Hz@10 kHz. The characteristics of this laser, such as long-time stability, repetition rate, and spectral stability, are investigated in detail. Besides, some typical lasing states in experiments are compared and analyzed.

This work studies the nonlinear Thomson scattering and its radiation properties when electrons interact with linear polarization lasers using a single electron model. By theoretical derivation and program simulation, electron motion trajectories at different initial phases are mirror symmetrical at 180◦ intervals. The influence of the initial phase of linear polarization laser pulse on the spectrum of high energy electron radiation is analyzed. Simulation results reveal that the radiation spectrum of high energy electrons at different phases has periodic symmetry, and the frequency of the peak of the spectrum decreases with the increase of the initial phase in one period. The peak value and the oscillation amplitude of the two-dimensional spectrum decrease with the increase of the initial phase and the energy distribution of the spectrum moves to the high frequency region with the increase of the initial phase. In addition, the electron radiation characteristics undergo a mutation when the initial phase changes in the range from 135◦ to 150◦. Based on the above simulation results, it provides theoretical guidance for further numerical simulation and study of high-energy electron radiation under linear polarization laser.

High power supercontinuum (SC) pumped by noise-like pulse (NLP) has become an attractive research topic. In this work, we experimentally demonstrate a high power all-fiber short wavelength infrared SC pumped by amplified 2 μm NLP. The mode-locked structure of NLP seed is based on nonlinear amplifying loop mirror (NALM) with repetition frequency of 6.3 MHz, pulse width of 5.491 ns and maximum output power of 187.2 mW. After amplification of two-stage thulium-doped fiber amplifiers (TDFAs), the obtained SC has spectrum ranging from ~1926 nm to ~2372 nm and the maximum output power of 90 W. As far as we know, this works achieves the highest SC power seeded by 2 μm NLP, demonstrating that the NLP pump has advantages of relatively simple structure and high power in generating SC.

In this work, we employed gain-managed nonlinear amplification (GMNA) technology to achieve a pulse characterized by a smooth spectral profile and an exceptionally wide spectral bandwidth. Then this pulse was injected into a chirped pulse amplification (CPA) system for amplification, and a high energy, narrow pulse duration fiber laser system was successfully built. The initial seed source for system was a self-made mode-locked fiber oscillator that utilized a nonlinear amplifying loop mirror (NALM). This oscillator produced ultrashort pulses with a pulse duration of 10.96 ps at a repetition rate of 11.52 MHz. The spectral width of the mode-locked oscillator was significantly broadened from 5.83 nm to 63.97 nm using GMNA technology. Furthermore, the spectral profile, which initially exhibited severe oscillation structures, was reshaped into a smooth profile through the application of GMNA. Subsequently, the pulse energy was increased through CPA amplification. Finally, in the case of a central wavelength of 1064 nm and a repetition rate of 500 kHz, a pulse with an average power of 20.02 W, a single pulse energy of 40 μJ, a pulse duration of 179 fs, and a peak power of 224 MW was obtained. This fiber laser system has great prospect of application in clinical medicine and precision manufacturing due to its high energy and ultra-short pulse duration.

We have demonstrated an end-pumped mode-locked femtosecond Yb:KGW laser which assisted by a semiconductor saturable absorber mirror (SESAM). By using a 2.5% output coupler, the oscillator generated average output power of 2.5 W which pulses duration was 192 fs at a repetition rate of 69.5 MHz, corresponding to a pulse energy of 36 nJ and peak power of 187 kW.

In this paper, we prepared side-polished optical fiber surface plasmon resonance (SPR) sensors, which are embedded in V-groove in quartz glass and are spattered with ~5 nm Cr and ~50 nm Au. The response performance of 50 μm SPR optical fiber sensor to the refractive index matching fluid was tested experimentally. When the refractive index range is 1.335 ~ 1.345, the full width at half maximum (FWHM) of resonant dip is 68 nm, and the sensitivity is 1370 nm/RIU. The surface plasmon wave (SPW) is excited by a broadband light source and a fixed wavelength laser source, and the corresponding detection methods are respectively maximum absorption wavelength detection, and fixed wavelength power absorption detection. The maximum absorption wavelength detection sensitivity is 2000 nm/RIU, and the resolution is 5 × 10^-6 RIU. The power absorption ratio detection method can realize resolution 3.5 × 10^-4 RIU.

An innovative black silicon (Si) with enhanced photoelectric performance was directly processed by femtosecond (fs) laser irradiation in ambient air. Followed by decorated with Au nanoparticles, this processed Si is shown to enhance the light absorption from the surface in a wide wave band, especially in the near-infrared range of 1.1 ~2.5μm, where the absorption of Au decorated black Si (B-Si-Au) nearly reaches to 70%, and displaying double magnitude higher than the bare black Si (B-Si). A systematic investigation of synergy effect between the hierarchical texture and Au NP-induced localized surface plasmon resonance (LSPR) is crucial to upgrade B-Si-Au absorption enhancement. On one hand, the processed microstructures on the Si surface may effectively extend the incident light path and thus provide more chance for the photon perennate into the Si and thus reducing reflection; on the other hand, strong scattered fields in the vicinity of Au nanoparticles generate extremely high intensity hot spots, which in turn lead further enhancement of absorption.

Glass fiber reinforced composite material (GFRP) is a functional material made of glass fiber as reinforcing material and synthetic resin as matrix material. GFRP has the advantages of high strength, fatigue resistance, corrosion resistance, etc., and is widely used in various industrial fields. However, the surface of GFRP is hydrophilic and easily wetted by water, which sometimes limits the practical application of GFRP. In this paper, we propose a method to prepare superhydrophobic GFRP surfaces using femtosecond laser direct writing combined with fluorosilane modification. By optimizing the laser parameters, the prepared superhydrophobic GFRP surface shows groove structures with a period of 25 μm and a depth of 40 μm. The surface possesses good superhydrophobicity and anisotropy wettability. In the vertical groove direction the contact angle is 158.7° and the sliding angle is 7.3° . In the parallel groove direction, the contact angle is 160.4° and the sliding angle is 5.0°.

An optically transparent metamaterial structure with broadband microwave absorptivity is proposed. A specifically designed optically transparent metasurfaces was designed to control the microwave absorption though properly modifying the impedance and resonance peaks of the meta-atom. Within a wide incident angle of ±60^o, the proposed structure displays high absorptivity greater than 90% in the region of 33.7-44.7GHz for TE polarization. For TM polarization, the absorptivity in the region of 11.8-37.2GHz is greater than 90%. The perfect consistency between experimental results and simulation results demonstrates that the proposal has practical application of multispectral stealth technology.

We report a passively Er3⁺-doped mode-locked fiber laser based on repetition rate multiplication, in which a three-stage Mach Zehnder interference structure is employed as a repetition rate multiplier. The initial soliton pulses are generated from a ring cavity with a fundamental repetition rate of 102.70 MHz, which is a seed laser. When the intrinsic frequency of repetition rate multiplier is almost aligned with a variable optical delay line, the initial repetition rate output from a seed laser, is lifted from 100.20 MHz to 801.03 MHz. This result demonstrates a method to achieve high repetition rate (> 500 MHz) pulse lasers, which avoids the limitation of cavity length on the repetition rate.

Microholes are the key structure of core components in aerospace, precision instruments, and other fields. Both the machining accuracy and surface quality play a key role in the performance of the components. Titanium alloy has good high specific strength, excellent corrosion resistance, and super fracture toughness and fatigue properties, but its poor thermal conductivity, toughness, and large friction coefficient, result in the processing of titanium alloy deep small holes being more difficult. This paper proposes Laser and Shaped Tube Electrochemical Machining (Laser-STEM), which utilizes the total internal reflection to guide the laser to the machining zone. In Laser-STEM, the laser-induced local temperature rise of the electrolyte and direct processing could benefit the removal process of electrochemical machining of titanium alloy. Experiments were carried out using a liquid-core fiber-optic tube electrode with an electrolyte of 12.5% sodium nitrate solution while processing micro holes on Ti-6Al-4V titanium alloy. The effect of pulse voltage, laser power, and feeding rate on the machining accuracy of deep small-hole in titanium alloy was experimentally studied. With the increase in laser power, the machining gap increased by 34.74% and the side gap decreased by 24.13%. The experimental results show that the laser can improve the electrochemical machining accuracy. The experimental results showed that a deep hole without a recast layer of 1.5 mm in diameter and 50 mm in depth could be obtained in the Ti-6Al-4V workpiece at a processing voltage of 20 V, a laser power of 5 W and a feed rate of 1.2 mm/min. This paper verified the feasibility of processing deep and small holes in titanium alloy by combining laser and electrochemical machining, and provided a new solution for the high-efficiency processing of deep small holes and surface structures of titanium alloy.

Recently, 2D materials have attracted considerable research attention in nanophotonic and integrated optoelectronic devices due to their intriguing thermal, mechanical, exciton and nonlinear optical response. Despite extensive efforts on various 2D materials (graphene, transition metal dichalcogenides, h-BN, etc.), however, a candidate material with large nonlinear optical (NLO) properties, ultrafast response speed, broadband response window and good thermal stability remains elusive. Black Phosphorus (BP) is a representative 2D semiconductors, which has huge potential for photodetectors, photo-catalysis, thin-film transistors and photodynamic therapy. In this study, we investigated the ultrafast NLO response of black phosphorus quantum dots (BP QDs)/water dispersions via Z-scan measurements with both femtosecond and picosecond laser pulses. We found a sign change of nonlinear refractive index n₂ of BP QDs from femtosecond to picosecond timescale. The dynamic response mechanism of BP QDs/water dispersions was studied by using femtosecond transient absorption spectroscopy under 355 nm excitation. A broadband absorption signal was observed ~0.5 ps after pump excitation, and the decay lifetime of this signal was rather slow (several nanoseconds). Our results indicate that BP QDs is a promising NLO material for ultrafast all-optical signal processing applications.

In order to study the influence of the laser intensity of linearly polarized laser on the radiation characteristics of single electron, a collision model between single electron and laser was constructed by formula derivation. MATLAB was used to write simulation program for numerical simulation and theoretical analysis, and the trajectory of electron was obtained. Then the radiation characteristics of single electron in three and two dimensions of linearly polarized laser with different laser intensities are studied. The results show that with the increase of laser intensity from 1 to 9, the maximum radial deviation of electron trajectory is further enhanced with the increase of laser intensity, and the axis position of the peak does not change. At the same time, the transverse amplitude and interference fringe number of the electron increase with the increase of laser intensity, and the spectral line broadening effect will appear more obvious, and the amplitude is not completely positively correlated with the emission power, and the peak value is reached at 6 and then decreases. However, the higher the laser intensity, the less monochromatic the spectrum is. The results provide more theoretical and numerical basis for the study of single-electron radiation characteristics, and provide reference for the further exploration of the parameters of ultra-strong laser.

The bound state in the continuum (BIC) is widely used in optical field confinement because of its potential in radiation suppression, providing an energy confinement method different from traditional microcavities. However, the size compression of BIC cavities still remains challenging. In this paper, we report an ultra-small size, high-Q BIC microcavity on silicon on insulator (SOI) platfom. We used the integer topological charges carried by the BICs to suppress the vertical radiation loss, while photonic crystal hetero-structures were utilized to reduce the transverse energy leakage. We designed and fabricated photonic crystal microcavity with optical confinement region as tiny as 5×5 period. The measured Q is greater than 170 thousand with the peak wavelength at 1550.39 nm. This work shows the potential of BIC microcavities in size compression. The study has positive effects on integrated optics, information optics, biooptics, topological optics and nonlinear optics.

Recently, narrow linewidth fiber lasers are widely applied in coherent detection and wavelength beam combining. In high-power linearly polarized narrow linewidth fiber lasers, the effect of mode instability (TMI) is one of the main factors limiting its power increase. In this paper, the influence of TMI effect on the output power of high-power linearly polarized narrow-linewidth fiber laser is analyzed, and the suppression method of TMI effect is proposed. Long-wave pumping technologies are used in this article. A single frequency laser with an output power of 100mW is used as the seed source. And the phase modulator broadens the linewidth of the seed source to 23GHz. After three stage amplification, the linewidth of 23GHz, power of 2.2kW, and center wavelength of 1064nm are finally realized. Linearly polarized narrow linewidth fiber laser output with extinction ratio of 98% is achieved. Beam quality is M²_x=1.2 and M²_y=1.21. The influence of the pump wavelength on the TMI effect is analyzed. Due to the small core diameter of the fiber (20μm), a high absorption coefficient of the gain fiber for the pump light (1.8dB/m@976nm), the core temperature is high. And the heat introduced by the pump photo quantum defect, causes the refractive index of the fiber core to change. Finally, the TMI effect occurs at lower power. When the pump wavelength is shifted to the long wavelength, the quantum defect of the pump light and the pump absorption coefficient are both reduced. The heat distribution on the entire length of the fiber or on the unit length is reduced. The TMI threshold is increased. And the output power of the linearly polarized narrow linewidth fiber laser is improved.

In order to achieve accurate superposition of array lasers in the far field and ensure the quality of the array laser synthetic beam, it is required that the array laser sub-beams point in the same direction, i.e., there is no tilt aberration between the sub-beams. To this end, a composite sensing-based array laser tilt detection and correction method is proposed, which combines single-lens detection with microlens array detection and can achieve large dynamic range, high accuracy and high bandwidth correction to a certain extent. The basic principle of the method is: for the large dynamic range of the array laser first use microlens detection and stochastic parallel gradient descent algorithm (SPGD) for coarse correction, when the array laser sub-beam into the microlens array range, use microlens detection and PI control combined to achieve fast and high precision correction of the array laser tilt aberration. The tilt correction effect of the composite sensing-based array laser tilt correction method is compared with that of the SPGD control algorithm alone and the PI control algorithm alone, and the results show that the iteration efficiency of this method is 3.5 times higher than that of the SPGD algorithm alone for the same tilt correction results, and the synthetic beam quality is significantly improved after the tilt correction. The composite sensing-based array laser tilt aberration correction solves the contradiction between large dynamic range and high accuracy and high bandwidth to a certain extent without significantly increasing the system complexity, and effectively improves the anti-jamming ability and environmental adaptability of the array laser, which has great potential and promising application.

Waterjet guided laser processing demonstrates effective reduction of the heat-affected zone and defects, including micro-cracks, recast layers, and burrs compared with long-pulse laser processing. Moreover, it surpasses ultrashort pulse laser processing in terms of processing efficiency. In this study, we meticulously investigated the impact of various parameters, namely feed speed, cutting time, parallel paths distance, and the number of parallel paths, on the cutting efficiency and quality of 1mm thick TA1 titanium plates. Through meticulous analysis using a laser confocal microscope, we evaluated both the upper surface morphology and three-dimensional characteristics of the cuts. The results are as follows: (1) The cutting efficiency gradually declines with increasing cutting speed and reaches its peak at a cutting speed of 1 mm/s and a material removal rate of 12.14 m/s. (2) In the case of single path cutting, the processing efficiency gradually diminishes with time, and the depth ended up at 900μm. (3) The cutting efficiency experiences an initial increase followed by a subsequent decrease with the augmentation of the distance between parallel paths and the number of parallel paths. (4) By adopting a feed speed of 1 mm/s, parallel paths distance of 50μm, and employing 5 parallel paths, we achieved a remarkable 183% increase in the material removal rate in cutting titanium compared with before the optimization, moreover, the cutting time is reduced by 65%. The average surface roughness before and after optimization are 2.93μm and 2.94μm respectively. Our research provides a theoretical basis for the study of waterjet guided laser cutting of TA1 titanium.

Ultra-stable laser with PDH (Pound-Drever-Hall) frequency stabilization technology is an indispensable tool in optical atomic clocks, gravitational wave detection, and optical fiber optical frequency transfer. As the demand for space and transportable science missions rises, the ultra-stable laser is required to have an auto-lock function. During auto-lock, the PZT is scanned in pre-set steps to find the resonance point with the optical reference cavity. To determine steps for the first lock automatically and update steps when pre-set steps are changed by long-term drift, the Grid Search algorithm with priori knowledge is utilized. To verify the reliability of the algorithm, the system out of lock is simulated 904 times. The relock with the parameters determined by the Grid Search algorithm is achieved with a success rate of 100% and a mean relock time of about 0.9s. The Grid Search algorithm with priori knowledge proposed in this paper can optimize the hyperparameters in auto-lock.

In this paper, the tunable narrow spectral semiconductor laser technology based on on-chip DBR gratings is investigated. The surface DBR grating structure and electro-thermal tuning structure were designed, determined key parameters of grating structural, and the problem of multi-peak suppression was studied. Developed manufacturing technology for surface DBR gratings and tunable technology based on micro-electrode heaters and applied them to tapered MOPA laser chips, achieving output laser spectral locking while maintaining the high brightness of tapered semiconductor lasers. The tapered MOPA laser has achieved a narrow spectral width of 40 pm and a side mode suppression ratio of 35 dB under a continuous-wave power of 10.3 W. At a microelectrode heater current of 0.22 A, the wavelength can be continuously tuned over a range of 4.3 nm, with a maximum spectral width not exceeding 60 pm.

Passively mode-locked fiber laser based on two-dimensional material MnPS_xSe_y saturable absorber is studyed. By changing the doping ratio of S and Se, three magnetic materials, MnPS_2.9Se_0.1, MnPS_2.8Se_0.2 and MnPS_2.7Se_0.3, are obtained. The three materials were fabricated into sandwich absorbers, and stable mode-locked pulse was obtained in ytterbium-doped fiber lasers. The total length of the fiber laser is 88 m, and the corresponding repetition rate is 2.27 MHz. The signal-to-noise ratio of the three materials is all above 60 dB, indicating the stability of the mode-locking pulse. The experimental results show that MnPS_xSe_y has good nonlinear optical modulation characteristics and optical switching ability, which has potential application value.

The 1.3 μm laser source has a wide range of applications in the fields of sodium beacons, optical communication, image display and laser medicine. In the paper, we demonstrate a laser with an LD end-pumped Nd:YAG slab crystal hybrid cavity Innoslab structure. When the pump power is high, the thermal effect of the laser during oscillation has an impact on the stability of the resonant cavity and the quality of the beam. We demonstrate a finite element model of an Nd:YAG crystal by means of heat conduction theory and analyse the effect of the temperature distribution at the crystal end face and the pump spot width on the thermal effect of the crystal. Calculations show that the finer the pump spot, the more pronounced the thermal effect of the crystal. In the experiment, the Nd:YAG slab crystal was doped at a concentration of 1at%, and a mixing cavity is constructed with a concave spherical mirror of R₁ = 1000 mm and a convex cylindrical mirror of R₂ = 900 mm; the length of the cavity is 55 mm; a negative cylindrical lens of Rc = -100 mm is inserted in the cavity as a compensating mirror. Finally, the maximum output power in the resonant cavity without the compensating mirror was 46.9 W; with the addition of the compensating mirror the maximum output power was 40.5 W; the vertical beam quality was increased from 2.98 to 1.28.

Optical vortices have captured considerable attention in the past several decades. The generation of a flexibly modulated vortex beam with super-high topological charge is always attractive for practical applications. Here, we combine random fiber laser (RFL) with digital micromirror device (DMD) based superpixel wavefront shaping, realizing the perfect vortex beam (PVB) generation with topological charge as high as 130 order. The resulting ultra-high topological charge PVBs inherit the advantages of low noise and none longitudinal mode oscillation from RFL, high fidelity and flexibility from superpixel wavefront shaping. It is anticipated that the proposed high-charge PVB can serve as a seed beam for the development of advanced structured light, which has great potential in the fields of optical manipulation, optical communication, and biphotonic.

The pharmaceutical industry extensively employs glass vials for the packaging of sterile preparations. Air invasion resulted from vial leakage leads to preparation quality deterioration. Tunable Diode Laser Absorption Spectroscopy (TDLAS) has been established as an effective non-contact method for assessing seal quality by detecting residual oxygen concentration in vial headspace. However, definitely unlike that the scheme of cavity-enhanced absorption spectroscopy (CEAS) has a sufficiently long optical path, headspace oxygen detection should be realized within the short inner diameter length of vials, while the external optical path is longer and with rich oxygen in the open production environment. Innovatively, we attempt to make full use of the cavity-like geometric nature of the glass vial to increase the inner absorption optical path length, by coating a high-reflectance silver ring film on the outer wall of vials. This novel scheme enables the incident laser to achieve Axial Section Multiple Reflection (ASMR) within space-limited vials (using ‘n-ASMR’ denotes the mode with ‘n’ times of reflections), extending the absorption path effectively without equipping any additional absorption cavity, we name it Cavity-Like Enhanced Absorption Spectroscopy (CLEAS), which breakthroughs the limitations of the conventional Direct Transmission (DT) method only along the diameter direction. In the Allan variance analysis tests, compare with the detection limit 0.226% with an integration time 33.8s of the DT method, our 2/4/6/8-ASMR methods achieve the detection limits 0.058%, 0.054%, 0.058% and 0.046% with integration time 28.9s, 14.6s, 4.76s and 5.60s, respectively, which indicate a brand-new roadmap has been discovered by the CLEAS scheme to extend absorption path in space-limited glass vial without increasing any hardware facilities.

With the development of ultrafast laser technology, the peak energy of ultrashort pulses continues to increase. In addition to the demand for energy enhancement, many frontier physical experiments also put forward more stringent requirements for signal-to-noise ratio (SNR) of lasers. When the petawatt-level laser interacts with the target for physical experiments, the pre-pulses interact with the target in advance, affecting the density scale length of the pre-plasma and changing the spectral distribution of the generated electrons. In order to meet the requirements of pre-pulse control schem, we developed a SNR active control module based on isolated pre-pulses, which generates an isolated pre-pulse with adjustable time delay and relative intensity. The time delay of the isolated pre-pulse can be continuously adjusted in the range of -1300 ps to 0 ps. At the same time, by controlling the number of attenuators in the pre-pulse optical path, the relative intensity of the pre-pulse can be adjusted in the range of 10^-8 to 10^-3. We placed the module in front of the main amplification chain of the ShenguangⅡ ninth picosecond petawatt laser, adjusted the time delay and relative intensity of the pre-pulse, and measured the SNR at the terminal. The results verified the feasibility of the SNR active control scheme based on isolated pre-pulse.

Publisher's Note: This paper, originally published on 16 October 2023, was replaced with a corrected/revised version on 29 November 2023. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.