To investigate the spectral properties of Laguerre-Gaussian ultrashort pulsed lasers transmission in a gradient refractive index fiber, the generalized Huygens-Fresnel principle was employed to deduce the analytical expression of the Laguerre-Gaussian ultrashort pulsed lasers transmission in a gradient refractive index fiber, and the reliance of the spectral modulation function on topological charge, radial index, and fiber transmission distance was analyzed. The research reveals that when the Laguerre-Gaussian ultrashort pulsed lasers is transmitted in a gradient refractive index fiber, the spatial distribution of the spectral modulation function and the spectral intensity undergoes periodic focusing and diffusion, yet the temporal-spatial coupling effect leads to their non-symmetrical distribution. For beams with different central wavelengths, the longer the wavelength, the higher the second peak of the spectrum after being modulated by the spectral modulation function. In addition, when the duration of the Laguerre-Gaussian ultrashort pulse laser is 3 fs and the transmission distance is certain, the spectrum splits into two peaks with equal peak heights at the off-axis position of 8.99 μm, and then the phenomenon of spectral switching can be observed, and the spectral shift rapidly jumps from the red-shift to the blueshift when the off-axis position crosses the point. This study offers theoretical support for the spectral variations of the Laguerre-Gaussian ultrashort pulsed lasers transmission in a gradient refractive index fiber and holds potential applications in information coding and transmission.

Direct writing with femtosecond lasers is the efficient and flexible 3-D precision material processing technology, which has been widely used in many fields. The optical waveguide is one of the basic configurations in an integrated photonic device, which can restrain the light field in a small channel for the diffraction-free propagation. In this paper, with the aid of the material modification and material ablation during the femtosecond laser processing, the directly-writting mechanism and the depletion of optical waveguides for different materials was summarized and analyzed. Researches utilized femtosecond lasers to realize the direct writing technology with low cost and high efficiency on materials such as glass, crystal, and polymers, ect. were reviewed. Finally, wthe prospect was made for the waveguides processed by femtosecond lasers in this review. It seems that the most critical factor during the laser manufacturing process of integrated micro-nano optical devices might be the low loss, high smoothness, high information fidelity, and 3-D fabrication of waveguides fabrication in the near future.

In order to study the detection ability of the laser shock detection method for “weak bonding” defects, carbon fiber reinforced plastic (CFRP) bonding specimens with different pollution levels were prepared. Tensile shear test was performed on the specimens first, and laser shock wave generation system was used to perform laser shock on them. The impact detection results were observed and compared with the results of tensile shear test. The results show that, the tensile shear strength of the contaminated specimens decreases by about 55% ~ 78% compared with that of normal bonding, and the failure mainly occurs at the bonding interface, which conforms to the characteristics of “weak bonding”. When the pulse width of the laser is 30 ns, the spot diameter is 4 mm, and the laser energy is 3.68 J, the normally bonded specimen begins to spalling, while the 2.76 J and 1.84 J laser energy shock can cause damage to the contaminated specimen without damaging the normally bonded specimen. The damage size is related to the bonding strength of the specimen, and the location of the damage is also consistent with the fracture location of the interface in the tensile shear test. The results indicate that laser shock detection can effectively identify weak bonding defects. This result is helpful to the development of weak bonding detection technology.

To investigate the machining characteristics of vector laser fields on silicon surfaces under water assistance, a nanosecond vector laser water-assisted surface machining system was developed. A Q-switched Nd:YAG pulsed laser was used to perform laser drilling experiments on 3 mm thick monocrystalline silicon. The effects of pulse number, beam polarization state, topological charge, and water flow rate on silicon surface machining were systematically studied under both static water and water-jet assistance. The results show that under water-assisted conditions, the heat-affected zone and recast layer are almost eliminated. Compared to linearly polarized light, vector beams produce larger hole diameters at high pulse numbers. Among generalized cylindrical vector beams, radial and azimuthal polarization, and higher topological charge vector beams, the latter results in smoother hole surfaces. Under water-jet assistance, when the water flow rate exceeds 0.8 L/min, the circular symmetry of the machined hole begins to degrade. However, compared to radial and azimuthal vector beams, generalized cylindrical vector beams better maintain hole symmetry. The combination of water assistance and vector laser technology enables more precise machining, demonstrating significant potential for industrial applications.

To examine the interference effects of a 532 nm nanosecond pulse laser on two representative image sensors, namely charge-couple device (CCD) and complementary metal-oxide semiconductor (CMOS), experimental studies were conducted in accordance with the testing methodology outlined in ISO-21254, under both atmospheric and vacuum conditions. The impact of varying pulse numbers within a 50 ms exposure duration was systematically compared and analyzed alongside the interference effects observed in different environments. The findings indicate that both CCD and CMOS are significantly influenced by the 532 nm nanosecond laser, resulting in optical saturation phenomena. Additionally, CCD demonstrates “reverse saturation” and “saturation crosstalk”. As the number of applied pulses increases, the quantity of saturated pixels exhibits a linear growth relative to laser energy density, with an accelerated growth rate corresponding to an increase in pulse count. Notably, CCD displays superior performance against interference effects in vacuum compared to atmospheric conditions; conversely, CMOS shows more pronounced interference effects when tested under atmospheric conditions but possesses greater resilience against 532 nm nanosecond pulse laser disturbances than its CCD counterpart. These research outcomes provide valuable insights for selecting detectors suitable for practical application environments.

In order to design a head-mounted display with a larger field of view, higher image quality, and a lightweight structure to meet the needs of high-end occasions, a two-chip head-mounted display was designed with a tiled aspheric and folded optical path system. Two lenses consist of a stitched aspherical surface, a planar surface, and two spherical surfaces were adopted, and the four surfaces were coated with a semi-transparent and semi-reflective coating, a phase delay film, a polarization reflective film, and an anti-reflection coating. Firstly, the initial structure was calculated by aberration theory, and then in order to further improve the imaging quality of the edge field of view, the stitched aspheric surface was introduced, and the tolerance analysis of the design results was carried out. The results show that the full field of view of the optical system reaches 100°, the modulation transfer function of the edge field of view is greater than 0.3 at the Nyquist frequency, the diameter of the exit pupil is 8 mm, the distance of the exit pupil is 14 mm, the total length of the system from the pupil to the image source is not more than 30 mm, and the total mass of the two lenses is only 21.0 g. The use of stitched aspheric and folded optical paths can significantly improve the performance of head-mounted displays, which can provide a reference for the research of high-imaging quality headband displays with large fields of view.

Laser internal modification processing technology, with its high efficiency, non-contact, and low loss advantages, is widely used in the field of semiconductor wafer cutting. To investigate the influence of laser focusing characteristics at different depths within the wafer on cutting quality, a spherical aberration correction was performed using the backward ray-tracing method. An experimental platform for laser internal modification cutting, based on spherical aberration correction via a liquid crystal spatial light modulator, was designed and constructed. Using a 1064 nm picosecond laser, experiments were conducted on a 350 μm thick silicon carbide wafer, resulting in an internal laser modification layer with a length reduction of 20%~30%. Furthermore, based on the energy loss of laser transmission within the material and the change in laser power density caused by spherical aberration correction, a method for regulating the focusing characteristics of laser internal modification cutting for silicon carbide wafers was proposed. The results indicated that by employing a variable power multi-pass scanning strategy, high-quality processing with a side surface roughness 819 nm and no edge or corner chipping was achieved using eight modification layers. This study provides a reference for optimizing the laser internal modification cutting process and enhancing the cutting quality of silicon carbide wafers.

To improve the processing efficiency of plasma spectra during laser welding/additive manufacturing processes, a professional software for automatically calculating characteristic parameters was developed, and a fitting goodness algorithm was used to quantify the matching degree between measured spectral data and fitted data. The accuracy and efficiency of the software calculation were verified based on the spectral data of AA6061 fiber laser-arc hybrid welding. The results show that the software can not only automatically select characteristic spectral lines and calculate characteristic parameters such as electron temperature and electron density in batches, but also provide accurate calculation results, with a maximum average deviation from the standard results of only 3.4%. Particularly noteworthy is the efficiency improvement in processing spectral data by over two orders of magnitude. Therefore, it can provide an efficient and accurate tool for processing plasma spectral information and is expected to offer a new approach for laser processing manufacturing and process monitoring.

Holographic lithography has garnered significant research attention in the production of 3-D micro/nano structures due to its high efficiency. To delve deeper into the morphological changes within these 3-D structures and evaluate the impact of exposure system design on production, a comprehensive exposure dose model within the photoresist was developed, rooted in holographic lithography principles. Additionally, a morphology evolution model for 3-D micro-nano structures was formulated. By utilizing these established models, theoretical analysis was conducted to investigated key variables influencing the contrast of the exposure field, including light source polarization, exposure substrate reflection, and incident light phase drift. Simulation results indicate that, within the classical reflective holographic lithography system, the transverse electric and transverse electric(TE-TE) polarized incident light exhibits superior contrast (above 0.95) across various incident angles, surpassing other polarization combinations significantly. Moreover, the reflectivity of the exposure substrate significantly influences contrast in the substrate’s normal direction, showing a positive correlation. Importantly, significant and low-frequency drifts in the incident light’s relative phase result in a notable decrease in exposure field contrast. Thus, actively mitigating environmental and internal disturbances is crucial for maintaining a high-contrast exposure field. This study provides a reference for the parameter optimization design of reflective holographic lithography systems.

In order to meet the application requirements of the frequency-stabilized lasers and make the laser frequency be freely locked in a certain range, a tunable laser stabilized to Fabry-Pérot (F-P) cavity using the Pound-Drever-Hall (PDH) technique was proposed. The laser frequency was locked on the F-P cavity by means of direct modulation of the laser current. The results show that, the fractional frequency instability turns out to be 5.3×10?12@1 s averaging time by analyzing the beat frequency from two identical lasers, which is three orders of magnitude better than free running. The linewidth of the stable laser is 381.68 kHz@10 μs and the 12 h power stability is 1.7×10?3. By controlling the F-P cavity length, the continuous tuning can be achieved over a range greater than 1.2 GHz and the tuning factor is 401.7 kHz/mV. The frequency-stabilized laser can reach the application target and its continuous tuning characteristics can effectively compensate for the limitation of the absorption cell as the frequency reference.

In order to solve the problem that the photoacoustic (PA) detection accuracy of dissolved methane (CH4) gas in oil is affected by water vapor, molecular relaxation analysis and experimental verification were adopted. The influence mechanism of molecular relaxation effects on PA gas detection was analyzed to explain the reason why environment humidity affects the CH4 detection accuracy. A distributed feedback (DFB) laser with the wavelength of 1650.9 nm was used to build CH4 gas detection systems based on a non-resonant PA cell with small volume. The synergistic effect of humidity and operation frequency of PA system on CH4 detection was verified by the experiments. A high-precision detection scheme was proposed to suppress the interference of water vapor changes on CH4 detection. PA signals of CH4 gas at different humidity and frequency were obtained. The experimental results show that the error of PA signal from low frequency to high frequency increases by 10% for dry methane gas. With the increase of humidity, the signal attenuation at high frequency drops from 13% to 2%. When the system works at 40 Hz with an integration time of 30 s, the detection limit of CH4 gas can reach 0.1×10?6. This work is of great significance to improve the online monitoring accuracy of dissolved gases in transformer oil.

In order to generate high birefringence in photonic crystal fiber (PCF), a special structure of PCF was designed, the core area was designed as diamond shape, and the cladding was arranged with hexagonal circular air holes. The transmission characteristics of the optical fiber, such as birefringence, confinement loss, dispersion, nonlinear coefficient and mode field area, were analyzed theoretically. The full-vector finite element method was used to calculate the birefringence as high as 0.0524 at the wavelength of 1.55 μm, and the confinement loss in the x-polarization direction was only 2.49×10?6 dB/m. The nonlinear coefficient can reach 52.512 W?1·km?1, and the mode field area is 2.4703 μm2. In the wavelength range of 0.95 μm ~1.85 μm, the dispersion in the x-polarization direction is (0.775±2.645) ×10?12 ps/(nm·km). This high birefringent photonic crystal fiber has a good application prospect in optical communication, optical sensing and other fields.

To improve the wear resistance of 45# steel surfaces and prolong their service life under different severe working conditions, different mass fractions of Fe/MoS2 coatings were prepared on 45# steel surfaces by laser cladding technology; scanning electron microscope and X-ray diffractomete were used to study the effect of MoS2 powder content on microstructure and phase composition of the coatings. Microhardness tester, friction and wear tester were used to conduct the related performance tests of a microhardness tester and friction and wear tester to analyze the correlation law of the coating hardness and friction and wear performance. The results show that the wear resistance of MoS2 coatings with different mass fractions is improved. The coatings are composed of cellular and columnar crystalline tissues and contain phases such as Fe, Cr0.5Mo0.5, Fe-Cr, etc. A small amount of face centered cubic phase is generated in the coatings with 15% and 20% MoS2 mass fraction. The coatings with a content of 15% MoS2 have a higher wear resistance; the hardness and wear resistance of the coatings with the addition of 15% MoS2 of the mass fraction are improved the most, and the hardness is 891.6 HV, the wear rate of the coating was 8.85 × 10?7 mm3/(N·m), and a coefficient of friction of 0.6523. Excessive addition of MoS2 resulted in a decrease in the hardness and wear resistance of the coatings. This study can provide a relevant research basis for improving the wear resistance of 45# steel surfaces.

In order to increase the number of orbital angular momentum(OAM) modes transmitted by a ring photonic crystal fiber and to optimize the mode dispersion and confinement loss during fiber transmission, a dual-conducting-mode ring photonic crystal fiber with near-zero flat dispersion and low confinement loss was designed in this paper. The fiber consisted of a six-layer refractive index ring auxiliary structure to isolate the inner and outer mode-conducting regions, and the outer cladding region was provided with three layers of air holes with gradually increasing radii. The finite element method was used to analyze the mode dispersion and confinement loss of the fiber by varying the refractive index and thickness of the high refractive index rings, the spacing of the air holes, and the radius of the air holes to determine the optimal structure. The results show that under the optical structure, in 1.5 μm~1.7 μm the dual-conducting-mode ring photonic crystal fiber can transmit 286+126 OAM modes, and the effective refractive index differences are all greater than 2.81×10?4 in both the inner and outer guiding-mode regions, the mode dispersion is in ?3 ps/(nm·km)~3 ps/(nm·km), and the mode confinement loss is in 2×10?9 dB/m~8×10?8 dB/m. This study provides a theoretical reference for enhancing the communication capacity and communication efficiency of photonic crystal fiber.

In optical systems, wavefront distortion caused by misalignment of optical components and atmospheric turbulence is the main source of wavefront aberration. The presence of wavefront aberrations affects the imaging quality of optical systems and has a significant impact on coupling efficiency, especially in optical devices and optical communication systems that require high precision. Based on the Zernike polynomial, the influence of specific single aberration modes in optical systems, i.e., circular-symmetric aberrations, tilt-coma aberrations, astigmatism aberrations, and wavefront distortion under the influence of atmospheric turbulence, on the coupling efficiency, and prospects for their development was reviewed.

In order to optimize the processing quality of microholes on the gas diffusion layer, the numerical model and experimental research method of laser ring-scanning hole making were used for theoretical analysis and experimental verification. The results indicate that the laser power has the greatest influence on the diameter of microholes, followed by the repetition frequency and scanning speed, while the depth of microholes is mainly affected by the repetition frequency. Theoretical and experimental results show that the influence of laser power on the diameter tends to decrease and then increase, while the repetition frequency continues to decrease. The optimal parameters for blind holes are 3 W, 1100 kHz, 900 mm/s, 20 μm spacing, and 10 ps pulse width at low processing times, respectively, and for through holes are 3 W, 600 kHz, 900 mm/s, 20 μm spacing, and 10 ps pulse width at high processing times, which is of practical significance for the processing of gaseous diffusion layer microvias.

In order to optimize the application of laser underwater cutting technology in nuclear facilities and ships and improve the cutting quality of Q235 steel plates, a method combining single factor and orthogonal experiments was adopted, while gas pressure, laser power and cutting speed were used as the main variables. And the experiment was carried out. The results show that gas pressure significantly affects the roughness of the cutting surface, and laser power has the greatest impact on the amount of slag. The optimal parameters are gas pressure 0.8 MPa, laser power 4 kW, and cutting speed 3.5 mm/s, respectively. At the same time, the cutting effect is best. Macroscopic and microscopic analysis also revealed that there is a layering phenomenon during the cutting process, which mainly includes the upper layer, the middle layer, the lower layer and the slag layer. This result will help further optimize laser cutting parameters and improve the accuracy and efficiency of underwater cutting of Q235 steel plates.

In order to analyze the interaction between ultrafast pulsed laser and 4H-SiC at atomic scale, the picosecond laser ablation process of 4H-SiC was simulated by molecular dynamics method of the two-temperature model, and the melting temperature, temperature field, atomic trajectory and ablation region of 4H-SiC were analyzed by different laser energy intensities. The results show that the interaction between picosecond laser and 4H-SiC is mainly thermal ablation, and the ablation process will be intense only after the end of the laser pulse, and the ablation process is more intense and the ablation region is more irregular with the laser energy intensity. The melting temperature of 4H-SiC crystal lattice is related to the system pressure. When the system pressure is 6.1 GPa, the melting temperature of the crystal lattice is 3230 K, which is about 400 K higher than the melting temperature of 2827 K under normal pressure, and the higher the system pressure, the higher the temperature required for the crystal lattice melting. This result provides a theoretical reference for picosecond laser for stealth dicing of 4H-SiC.

In order to meet the detection requirements of the orientation of the incoming laser beam in the laser alarm scenario, a surface mask coding laser angle detection component based on Gray code was designed. A new coding mode of 10 bit coding was adopted, in which 7 bits, 1 bits and 2 bits were used as angle coding, positive and negative coding and reference bits respectively. A new 2-D surface mask plate was designed. The detection field of view angle was ±30°, the resolution was 1°, and the appropriate irradiation intensity threshold was selected to accurately distinguish the code “0” and “1”. Through simulation software, the optical trace and irradiation intensity of the detector target surface under different angles of view were obtained, and the irradiation intensity values were normalized. The results show that the coding results identified by the light trace are basically consistent with the designed coding table. Using 47.5% of the average irradiation intensity of the reference bit sensor 10# as the threshold, the code “0” and “1” can be accurately distinguished. The detection component enables a more uniform beam intensity distribution, avoiding the edge effects and inhomogeneity that can occur with traditional flat masks. The design of high resolution angle detection module based on Gray code is feasible, and the research provides a reference for detection signal processing in laser alarm applications.

Laser welding has the advantages of high energy density, high welding efficiency, small welding deformation and high reliability of welding structure, which has a broad application prospect in rail vehicle manufacturing. Focusing on the requirements of rail vehicle for welding deformation control, welding efficiency improvement, reliability improvement of welding structure, lightweight design and manufacturing, the corresponding laser welding application scenarios were analyzed from the perspective of rail vehicle materials and structures, combined with application research cases, and the key advantages and potential challenges of laser welding in rail vehicle manufacturing were extracted. In view of the limitations of laser welding in engineering application, this paper expounds the methods of effectively carrying out laser welding process verification and realizing engineering application, and puts forward the key technologies that should be paid attention to and studied in the process of laser welding. This research can be used for reference to understand and develop the application of laser welding in rail vehicles.

The short-wave infrared band contains a variety of spectral information of the target and has good atmospheric transmission characteristics, which is one of the important bands for optoelectronic detection, laser communication and other applications. Silicon-based optoelectronic devices have the advantages of low power consumption and high bandwidth, but their spectral response range is limited to the visible band, making it difficult to directly carry out high-response photodetection in the short-wave infrared band. Therefore, the photoelectric integration of high short-wave infrared absorption ability of indium gallium arsenic (InGaAs) materials and silicon (Si) materials, and the development of a new type of high-sensitivity photodetector has become the hot direction of the current research. As the core technology of ultra-high-speed, low-power, miniaturized semiconductor optoelectronic devices, optoelectronic integration technology has strongly supported the leapfrog development of a new generation of information technology, such as big data, cloud computing, and the Internet of Things. By combing the domestic and international research and development history, current status, and future trends of optoelectronic integration technology, focusing on InGaAs-Si based photodetectors, the material epitaxial growth, flip chip integration, chip/wafer bonding, and other new optoelectronic integration processes were discussed. The characteristics, advantages, shortcomings, and usage scenarios of different optoelectronic integration technologies were analyzed, and the future development direction of optoelectronic integration technologies was envisioned.

In order to measure the stacked volume of filamentary material on the conveyor belt in real-time and accurately, a laser sensing technology was used to establish an online measurement method, combined with the smoothing algorithm of material surface contour point cloud data. Theoretical analysis and experimental verification were conducted to obtain the measurement accuracy and repeatability data of stacked volume after processed by three smoothing algorithms. The results show that, the height, width and cross-sectional area of the material accurately can be obtained, but the repetitiveness of volume is bad, whose variation coefficient is close to 5%. The smoothing effect of Moving algorithm is best. After the contour data is processed by Moving algorithm, the range and variation coefficient of volume decreased to 105.20 cm3 and 1.36% respectively, the single accuracy and multiple repetitiveness are both greatly improved. The results are helpful to improve the control stability and various indicators of process in cigarette production.