This PDF file contains the front matter associated with SPIE Proceedings Volume 12060, including the Title Page, Copyright information, and Table of Contents.

In recent years, ultrafast laser processing metal film has attracted widespread attention for its possible application prospects in the fields of electronic information and biomedicine etc. Among them, nano-bump on metal film induced by single pulse laser has significant value in industry of new energy and biosensors etc. Experiments are carried out to explore the bump deformation induced by ultrafast laser in this study. The deformation and ablation crater of gold film induced by single ultrafast laser pulse are observed by Scanning Electron Microscope (SEM) and measured by Atomic Force Microscope (AFM). When laser fluence is lower than 0.35 J/cm², there is no change on gold film exposed to ultrafast laser irradiation. Bump deformation happens when laser fluence exceeds 0.36 J/cm², with some cracks appearing. The height of bump is increasing by the increase of laser fluence and the number of cracks is also increasing. Ultimately, some crack is extremely damaged and the hole is formed on the top of bump

Aluminum alloy is widely used to make building panels, doors and windows, curtain walls, automobile decorative parts and aircraft skin due to its corrosion, surface treatment, beauty and durability. There is usually a dense oxide film on the surface of aluminum alloy. The oxide film has many pores, and the pore size becomes larger from the inside to the outside. It has good adsorption capacity and strong adhesion with the substrate. Therefore, it is necessary to pretreat and clean the oxide film of aluminum alloy. Compared with the traditional cleaning method, laser cleaning is an advanced environmental protection cleaning technology. Laser cleaning method has the characteristics of less environmental pollution, no contact, less wear on the substrate, high flexibility and stability, which can realize automatic cleaning, wide application range and good cleaning effect. But the key problem of cleaning is to determine the laser cleaning threshold and damage threshold. Firstly, the experiment of laser cleaning aluminum alloy oxide film was simply carried out, and the cleaning threshold and damage threshold were roughly determined by the morphology characteristics. In the theoretical part, the cleaning threshold is obtained by heat conduction model and numerical calculation analysis. Finally, it is found that the theoretical calculation results are consistent with the experimental results.

All-solid photonic bandgap fiber (AS-PBGF) has been an unrivalled platform for the effective mode area (EMA) scaling of large-mode-area fiber and the selective spectral filtering. Super-large EMA scheme assisted by the multiple resonance mechanism is also achievable while maintaining the robust single-mode (RSM) operation. In the current work, we have proposed aother modified multi-resonant AS-PBGF with some high-index nodes are replaced by the background material. By extending the multi-resonant coupling concept, a specially designed microstructural cladding, with multiresonant cores in the inner layers and leakage channels in the outermost layer, is employed to generate broadband resonance and modal dissipation of high-order-modes (HOMs) under bent configuration. Sufficient confinements on the modal distribution of fundamental mode (FM) are retained by adjusting the arrangement of Ge-doped rods in the microstructure cladding precisely, and the rotational symmetry of the proposed AS-PBGF makes it insensitive to bending direction. The missing Ge-doped rods in each layer are properly designed to stress differential bending loss between FM and HOMs with high loss ratio. Bending loss of FM less than 0.05 dB/m and high loss ratio over 200 times are always available and independent of bending direction. An EMA greater than 900 μm² and a loss ratio up to ~ 495 can be obtained under the bending radius of 45 cm.

A hybrid double cladding EYDFA with SMS structure is proposed and theoretically analyzed. The hybrid gain fiber with SMS structure is composed of two kinds of EYDFs with different core diameter. The output power performance and output spectra of the amplifier with hybrid gain fiber are numerical analyzed, and are compared with that of the amplifier with uniform gain fiber. The simulation results demonstrate that this fiber amplifier with SMS structure gain fiber can suppress the Yb-ASE by over 10 dB without output power reduction. It provides a monolithic structure for EYDFA to overcome pump bottleneck effect and achieve high efficiency and high power output.

Air-to-air missile is the main source of air confrontation, which plays an important role in air confrontation. The attack ability of air-to-air missile is one of the key factors of air combat. Establishing the models of motion and seeker tracking and introducing the greedy algorithm to improve the tracking ability, while regarding the third flight as attack target and establishing the model of motion and radiation. Simulating the infrared radiation characteristic of the target, calculating the attack region of missile and the optimization performance of algorithm It’s concluded that attack region of the simulation matches the reality and the greedy algorithm can usefully improve the recognition efficiency of seeker.

We demonstrate a common diode-pumped Q-switched Tm/Ho composite laser with a developed compact hybrid cavity, where the lasing wavelengths were changeable between Ho laser and Tm laser via modulating the cavity losses by changing transmittances of the crystalline Cr:ZnSe saturable absorbers (SAs) or using the output couplers between broad band coating and narrow band coating. Using a common 808 nm diode laser as the pump source, maximum Q-switched Ho laser power of 707 mW at 2091 nm, with pulse energy of 50.7 μJ and peak power of 99 W at 13.4 KHz was obtained among using the NCs. Among the BCs, maximum Q-switched Tm laser power of 413 mW at 2011 nm, with pulse energy of 35 μJ and peak power of 104 W at 11.7 kHz was obtained. Combing both advantages of Tm laser and Ho laser, a wide scope of applications including detection, commutation, and medical treatments are expected from the proposed laser source due to its accessibility, multifunction and miniaturization.

Aperture truncated Airy beam has unique properties such as non-diffracting, self-healing and free acceleration, and has wide application in optical micromanipulation, light bullets, filamentation, optical routing, and optical communication etc. Based on Huygens-Fresnel diffraction integral, propagation and evolution characteristics of several aperture truncated Airy beams such as exponential decaying, spatial domain truncated, frequency domain truncated and constant amplitude Airy beams are compared and analyzed. Effects of transverse scaling factor on non-diffracting propagation distance and transverse acceleration are discussed. Results show that the non-diffracting propagation distance and transverse acceleration offset increase with the increase of transverse scaling factor when the aperture truncated width is fixed. If the aperture truncated width and transverse scaling factor are the same, the non-diffracting propagation distance of frequency domain truncated Airy beam is the shortest, that of the exponential decaying Airy beam and the spatial domain truncated Airy beam are longer, and that of the constant amplitude Airy beam is the longest.

In this paper, we report two types of dual-wavelength pulse superposition states, i.e., heterogeneous and homogeneous pulse patterns, in a ring fiber laser mode-locked by nonlinear polarization rotation (NPR) with a Fabry–Perót (F–P) minicavity. The heterogeneous pulse pattern is characterized by the coexistence of the triangular spectrum and soliton-like spectrum with central wavelengths of 1558.3nm and 1565.4 nm, respectively. Meanwhile, the homogeneous pulse is formed by the superposition of two solitons whose central wavelengths are 1558.7 nm and 1565.6 nm, respectively. The switching between heterogeneous and homogeneous pulse patterns is realized through adjusting polarization controllers and the pump power. Theoretical analysis shows that the two-type pulse superposition state generation is due to two independent filtering effects in the fiber laser, which originate from NPR and F–P filtering effects, respectively. Our results will provide a new method to produce abundant dual-wavelength pulse patterns.

In recent years, 1.3 μm lasers have been widely used in laser medical treatment, optical fiber communication and optoelectronic countermeasures, etc. In this paper, the unstable cavity structure with double pump cavity connected in series and the method to optimize the thermal lens effect are used to obtain a maximum 41 W average power of continuous-wave laser. Meanwhile, the pulsed laser is realized through an acousto-optic Q switch and the repetition rate can be adjusted in the range of 1~10 kHz. The maximum single pulse energy can reach 8.44 mJ with the repetition frequency of 1 kHz, corresponding to 65 kW peak power. In the future, the output power will be further improved by optimizing the laser, which will be beneficial to expand the applications in related fields.

An all-fiber system based on the principle of optical waveguide self-imaging for coherent beam combination (CBC) system is designed. A square fiber is used as the beam combination device for all-fiber CBC system. The self-imaging characteristics of the square fiber are studied. The self-imaging effect of the square fiber is verified by theoretical simulation and experiment. The square fiber has good self-imaging characteristics and is suitable for CBC using its self-imaging characteristics.

High speed railway vehicle bogie is welded together with steel plate and tube. Butt joint is one of the main types joint traditionally welded with gas metal arc welding (GMAW) method. Hybrid laser-arc welding method, as an efficient welding method, has many advantages comparing with traditional GMAW, such as deeper penetration depth, smaller heat-affected zone (HAZ) and so on. In high power laser-arc hybrid welding, the stability of keyhole is related to the welding quality of back. In this paper, the butt joint root pass by hybrid laser-arc welding of S355, which is the commonly material of bogie, was studied. Welds back formation were analyzed by orthogonal test. Three parameters were designed as orthogonal factors, which were laser power, root gap and Distance between laser and arc (DLA). Three typical defect modes and the relationship between welds back formation and parameters were summarized. The evaluation scores were obtained from the appearance of test welds. Experiments show that the root gap width has the greatest influence on the back welds formation, followed by laser power and DLA. The Optimum parameters for the root pass of hybrid laser-arc welding process was concluded, which are laser power of 7.3kW, the root gap of 0.4mm and DLA of 3.5mm

We mainly study the conversion efficiency of Erbium/Ytterbium (Er/Yb) co-doped silicate glass fiber (Nufern PM-EYDF-12/130-HE) under different pump wavelengths, pump methods, gain fiber length and input signal power. Through a series of experimental studies, it is found that the hybrid pump mode of multi-mode pump diodes at 976 nm and 915 nm/940 nm are more efficient than that of single-wavelength pumping. When the input signal power is 85 mW, the fiber length is 3.9 m, the hybrid pump power of 976 nm and 940 nm is 10 W respectively, the output optical power can reach 6.41 W, and the optical-to-optical conversion efficiency is 33.7 %, and the signal-to-noise ratio (SNR) is more than 45 dB. When the hybrid pump power of 976 nm and 915 nm is 10 W respectively, the output power can reach 6.31 W, and the PPCE is 33 %. Under the condition of 20 W reverse pump power, the optical-to-optical efficiency of 976 nm, 915 nm and 940 nm single-wavelength pump is 30.7 %, 25.2 % and 21.7 % respectively.

Bronze cultural relics are an important part of Chinese traditional historical and cultural heritage. With the rapid development of ultrafast lasers in recent years, picosecond lasers have gradually been used in laser precision processing due to their controllability, reliability and low cost. With the increase of laser power, the laser ablation effect will occur[1].The contaminant on the surface of bronze cultural relics are thinner compared to that on other type of cultural heritage and need more accurate cleaning method needs to be used for removing contaminants without damaging the substrate of bronze relics. In 2013, Zhang Xiaotong et al. used wet laser cleaning technology to perform laser cleaning on the gilt bronze statues provided by Hebei Cultural Protection Center. They changed the power density, conducted preliminary trials of bronze cleaning [2]. In 2018, Shen Yijia et al. used agar gel and laser combined method to protect the bronze cultural relics from laser damage[3].

The laser guided missile has the advantages of strong anti-jamming ability and high accuracy of hit, which plays an important role in the past war. Compared with the active laser system, the semi-active laser system has the advantages of concealment, which makes the missile structure more simple and compact and the volume can be effectively reduced. The four quadrant detector is an important component of the seeker. Servo control system receives signal deviation to achieve target acquisition and tracking. The performance of the detector and control system of the semi-active laser servo platform directly determines the performance and strike capability of the whole missile system. This paper analyzes the algorithm and performance of the four quadrant detector in angle measurement, summarizes the types and action mechanism of laser interference, put forward the classification of active interference and passive interference. The characteristics of the semi-active laser detection system control system are analyzed, and the improved design is carried out on the basis of the traditional PID control system model. By introducing the disturbance compensation method and the method of adding the state observer based on speed and acceleration, the tracking speed and precision of the control system are improved. Finally, the effectiveness of the method is verified by simulation.

By using the extended Huygens-Fresnel principle and the definition of Wigner distribution function, influence of turbulent biological tissues on the propagation quality of VPCHG beam is studied by the derived analytical expressions. The numerical simulation results show that the effective radius of curvature of a VPCHG beam is smaller with decreasing beam width, decreasing the coherence width or decreasing beam order in turbulent biological tissues, and effect of the beam wavelength on the ERC of a VPCHG beam is slight. Besides, the normalized M²-factor of a VPCHG beam with smaller beam width or coherence width spreads slower than that of those with lager numbers, which implies that a VPCHG beam is less affected by the turbulent biological tissues. Additionally, the normalized M²-factor of a VPCHG beam is more smaller with the larger beam orders or larger beam wavelength. The propagation quality of a VPCHG beam would be controlled in turbulent biological tissues optical communications

A tunable passively mode-locked fiber laser with cylindrical vector beams (CVB) generation in a linear cavity was presented. The mode-locking mechanism is based on the nonlinear multimode interference effect of the graded-index multimode fiber (GIMF). The Sagnac loop mirror works as a filter. An ultra-broadband long-period fiber grating (UBLPFG) with a high conversion efficiency < 90% from 1004 nm to 1068 nm is used to covert fundamental mode to higher-order modes. The laser can achieve a continuously tunable wavelength range from 1032.344 nm to 1042.556 nm by changing the reflection spectrum of the Sagnac loop mirror thermally. When the laser operates at the central wavelength of 1042.556 nm, the output pulse trains have a period of 92.08 ns with pulse duration of 1.15 ns. The slope efficiency of the laser is about 4.73% with the mode-locking threshold of 167.7 mW. The purity of the radially and azimuthally polarized beams is measured to be higher than 93.8%.

In this paper, an automated edge detection model is developed for large irregular circular using a laser scanning approach. Some key influencing factors, just like surface quality, surface orientation and scan depth, have been respectively considered in this model. By consider of the limited of field of view and corresponding optical constraints, only a small part of key region is effectively captured by laser scanner at a specific posture. In term of specified view angles of laser scanner, the position of laser scanner approximate to the stand-off distance with respect to edge area can be determined and then high-quality point clouds of large irregular circular edge feature can be effectively obtained. Finally, a series of experiments are performed on workpieces with different large irregular circular features. The experimental result shows our method features high automation and high efficiency. Those results are most promising for on-machine applications in dimensional measurement of large-scale workpiece.

We report the cascaded generation of mid-infrared Raman solitons in an Erbium-doped fiber laser (EDFL) with a tunable Fabry-Perót filter. The first- and second-order Raman solitons were experimentally achieved at 1856 nm and 2029.6 nm, respectively, under pumping by a 1530-nm continuous wave (CW) laser with a 3-dB bandwidth of 0.1 nm generated from the EDFL. Their 3-dB bandwidths were 13.4 nm and 2.4 nm, respectively. It was found that the balance of Raman gain induced by nonlinear effects broadening the laser spectrum and Fabry-Perót filtering narrowing the laser spectrum in the EDFL resulted in the cascaded generation of Raman solitons within the wavelength band from 1800 to 2100 nm. It is the first time for a mode-locked EDFL operating at the wavelength band of 2.0 μm. Our work has great potential application as a novel optical source from near- to mid-infrared regimes.

We demonstrate a power combining pulse laser system with 1 kW average power output based on spectrum filtering of four subset pulse amplifiers. The output spectrum with and without spectrum filtering are compared. The result shows that, without spectrum filtering, nonlinear spectrum component from subset amplifier will accumulate along the QBH fiber and leads to serious spectrum broadening as well as stimulated Raman scattering (SRS) effect. By spectrum filtering with a band pass filter (BPF) inside the subset amplifier, nonlinear spectrum component is successfully mitigated and high purity spectrum pulse laser output is also achieved at the output power of 1kW.

The laser pulse broadening and delay caused by cloud and aerosol can degrade the data transmission rate. The pulse broadening and the time delay induced by atmosphere channel are analyzed. Then the corresponding performance of communication rate for DSOC system which based on PPM scheme are investigated.In this paper, both the pulse broadening caused by cloud, aerosol and atmospheric turbulence and the time delay induced by turbulence are analyzed. Then the corresponding performance of communication rate for DSOC system which based on PPM scheme are investigated. Numerical results indicate that the cloud physical thickness and aerosol particle optical thickness can affect the communication rate severely. But, the rate can be improved by choosing lower modulation order and initial pulse width under clear atmosphere condition. The results enable us to determine suitable parameters in practical applications for better communication rate.

Generation of noise-like pulses in a nonlinear Yb-doped fiber amplification system is investigated in three pump configurations: forward pump, backward pump, and bidirectional pump, respectively. Noise like pulse with a pedestal width as short as 2.99 ps is obtained. The average powers, pulse spectra and auto-correlation traces are measured. The characteristics of noise-like pulses generated in different pump powers and pump configurations are discussed.

In this work, we propose, to the best of our knowledge, the first demonstration of a ~3.5 μm dual-wavelength pumping (DWP) Er³⁺-doped ZBLAN fiber laser gain switched by 976 nm pulses. The DWP scheme is composed of a pulsed 976 nm laser system and a home-made continuous-wave 1973 nm laser. Stable pulses were obtained with repetition rates ranging between 5.2 kHz and 10 kHz. The maximum output power energy of 50.4 μJ was achieved at 10 kHz with a wavelength of 3445.9 nm. The temporal profile of the pulse trains was characterized by stable relaxation spike pulses containing a series of sub-pulses. The pulse characteristics with respect to the pump energy and the underlying mechanism are discussed. This work makes an effort to better understand the dynamics and theory of the cascade pumping system, and provides a new perspective for the realization of high-power pulses beyond 3 μm.

We use the full vector beams propagation method (VFE-BPM) to simulate the nonlinear propagation process of the cylindrical vector beams (CVBs). We have shown that the CVBs have poor transverse stability which causes which causes the breakup due to the ring-shaped beam field. Then, we use the approximate analytic theory to qualitative analyze the variations of the numerically calculated instability growth rates, which shows excellent agreement with the simulated results.

We propose and experimentally demonstrate a Yb-doped random fiber laser with a controllable oscillating mode based on injection locking technology. An external signal light is used to realize the locking of the transverse mode. By simply adjusting the injected signal light power, random fiber laser can directly oscillate at the LP₀₁ mode, hybrid mode, and LP₁₁ mode, respectively. Besides, random lasing with a low threshold and high slope efficiency can be obtained.

The near-infrared picosecond laser ablation characteristics (threshold, heat-affected zone (HAZ) and morphology) for graphitized carbon fiber-reinforced cyanate ester resin (M55/BS-4), a mesoscopically heterogeneous composite, were studied. The ablation threshold and its incubation effect for the composite were measured based on the diameter-regression method, with the single-pulse threshold derived from the incubation model. The influence of incident laser fluence (0.6-26J/cm²) and beam scanning speed (0.8-5m/s) on the ablation quality were analyzed. It was show that the ablation threshold, morphology and thickness of HAZ can be controlled by processing parameters for the composite. Well-defined groove with clear edge and minor HAZ, probably an indication of mesoscopically uniform removal for the material’s heterogeneous structure, was obtained by using a proper combination of scanning speed and incident fluence. A satellite-used carbon-fiber skin as large as 1m² based on laser cutting was demonstrated by using further optimized processing parameters.

The influence of the flow state on the performance of the ejector is always a hot and difficult problem in the design of the ejector. Aiming at an integrated low-pressure cavity and ejector structure, this paper uses numerical simulation method to analyze the flow field characteristics of the ejector under the conditions of zero injection, secondary flow injection and secondary exothermic reaction flow injection. The relationship between the position of the first oblique shock and the outlet back pressure is given. The flow field structure and start-up process of the system in the cold secondary flow state are analyzed. Then, considering the exothermic reaction flow, the influence of the residual exothermic reaction in the ejector on the start-up performance of the system is analyzed. The results show that the reverse pressure gradient caused by residual exothermic reaction is the main factor affecting the start-up performance of the system.

Efficient cleaning of pollutants on the optical lens surface is a very important and urgent research topic in the field of laser processing. Therefore, based on the free jet theory of fluid dynamics, the flow field characteristics of the optical system lens are theoretically analyzed and numerically simulated, and the flow field distribution of the lens surface and far field is given. And then, combined with the existing solid particle pollutants adhesion type, influence law and calculation model, the adhesion force of solid particles with different diameters is calculated quantitatively. According to the gas dynamic pressure distribution on the surface of optical elements, the effectiveness of solid particle blowing on the surface of optical elements is analyzed and evaluated. Finally, according to the secondary dust phenomenon of mirror free jet purging, the jet outlet size, downstream collection port size and jet velocity that affect the flow field distribution characteristics of the lens surface are optimized. Finally, a self-priming mirror jet purging structure without backflow is given, which effectively eliminates the secondary dust phenomenon caused by mirror purging.

In order to solve the physical field quantity that characterizes the laser irradiation effect by the transient temperature， using the finite element-finite difference numerical hybrid algorithm, the absorption coefficient, specific heat capacity, thermal conductivity, density and other dynamic target characteristic parameters that change with temperature are introduced. Based on the melting process of continuous laser action target obtained by equivalent specific heat capacity method, the simulation model of the temperature of the target irradiation process with the laser characteristics such as power and action time is established. For a silicon-based CCD target with a composite structure, a two-dimensional model is established during the calculation of the silicon-based CCD, and the thin-layer grid of the composite structure is encrypted. The maximum temperature of the upper surface center point of the aluminum layer of the silicon-based CCD with the action time under the continuous laser characteristic power is simulated. The maximum temperature of the center point on the upper surface of the silicon-based CCD varies with the power under different continuous laser characteristics. And the relationship between the temperature of the upper surface of the silicon-based CCD and the power under the fixed continuous laser characteristic time is simulated.

All-fiber wavelength-tunable fiber laser is a desirable light source architecture in many fields owing to their low cost, compactness and easy integration. However, most of them have independent filter elements and saturated absorption elements, which will undoubtedly increase the redundancy of laser. In this paper, we realize an all-fiber wavelength-tunable Ytterbium (Yb)-doped laser with the tunable central wavelength from 1023 nm to 1076 nm based on fiber loop mirror (FLM). The fiber loop (FLM) fused with two segments of polarization-maintaining fibers (PMF) acts as both a comb filter and a saturable absorber (SA). We believe that lasers with a simple structure and wide wavelength tuning range will have potential applications in sensing, communication, spectroscopy, and medicine.

All-polarization-maintaining (PM) fiber oscillator based on nonlinear amplifying loop mirror (NALM) modelocking has important applications for chirped pulse amplification systems. In this paper, we report an all-PM-fiberintegrated femtosecond chirped pulse amplification (CPA) system operating at 1030 nm, which consists of a NALM oscillator, an ytterbium-doped amplifier and a chirped volume Bragg grating (CVBG) compressor. The laser produces linearly polarized, linearly chirped pulses that can be recompressed down to 711 fs, corresponding to 95% compression efficiency. All-PM NALM fiber oscillator combined with CVBG compressor is a promising method for CPA system due to its extremely compact and robust architecture.

In this paper, we propose a non-contact real-time centroid measurement method for non-cooperative targets, which calculates the coordinates of the centroid point of the motion model in real time at a frequency of 30 Hz. The TOF (Time of flight) camera configuration, working principle and point cloud preprocessing technology including point cloud fusion of the measurement system are presented. Through the XYZ coordinates of the point cloud data, we calculate the centroid point position of the model. Experiments show that the measured centroid point XYZ three-axis accuracy is about 0.1mm.

Green-red (500nm-660nm) laser is widely used in laser projection, laser color display, lithography and laser communication. It is a relatively simple and effective method to obtain the green, orange and red laser from Pr3+:YLF crystal pumped by blue laser diode (LD). In this paper, the influence of output mirror with different transmittance and different curvature radius on the output power of green laser is analyzed. The green laser is achieved with the maximum output power of 960mW at 522nm, when the full pumping current is 2.269A, the absorption power of a-cut Pr³+:YLF crystal is 7.44W.

In this paper, temperature change and removal depth of continuous laser removal of various coatings (alkyd paint, epoxy varnish, epoxy primer) were analyzed by finite element simulation software. The simulation results show that under the condition of continuous laser irradiation for 1 s, the optimal cleaning threshold of double-layer structure target composed of epoxy primer and epoxy varnish is 200 W/mm², and the optimal cleaning threshold of three-layer structure target composed of epoxy primer, epoxy varnish and alkyd paint is 150 W/mm². The reason for this phenomenon is explained by the different material properties of each layer of coating. At the same time, it is concluded that the temperature when the laser directly acts on the double-layer target is lower than that when the laser acts on the three-layer target, which is conducted by alkyd coating. The results achieved in this paper can provide a feasible process parameter for related industries.

Deep ultraviolet laser (wavelength less than 200nm) has a wide range of applications in laser medical, material microprocessing, laser lithography, and other cutting-edge laser technology. The nonlinear optical crystal can transform the frequency of the common band laser and produce deep ultraviolet light, which is the focus of the current laser technology research. However, the growth of crystals is time-consuming and labor-consuming. Even if some crystals are grown, their properties may not be satisfactory. In the past decade, thanks to the development of high-performance computers, the computational research scheme based on the first-principles simulation has been developed, which promotes the development of deep UV NLO crystals and guides the follow-up and further experimental exploration. At present, some mature nonlinear crystals such as BBO, CLBO, and LBO can generate deep UV lasers by nonlinear frequency conversion, but their performance is not as good as KBBF. In this paper, the band gap, band structure, and optical properties of CaB₅O₇F₃ in the KBBF family are calculated by the first-principles theory.

A single-polarization single-frequency (SPSF) 1030 nm distributed feedback (DFB) fiber laser with mode switchable output is achieved. The DFB fiber laser is realized based on a 5 cm long π-phase shifted fiber Bragg grating (PS-FBG). A maximum output power of 84 mW with single-polarization operation is achieved. The polarization extinction ratio (PER) is around 17 dB and the linewidth is 18 kHz. The slope efficiency is 13% and the spectrum at the highest power shows an excellent optical signal to noise ratio of about 75 dB. Moreover, LP₁₁ mode single-frequency lasing is achieved by adopting an acoustically-induced fiber grating (AIFG). The mode purity is estimated to be higher than 96%. These results, to the best of our knowledge, show the highest output power among the reports that achieve single-frequency 1030 nm DFB laser output with single-polarization operation. Furthermore, it is the first time to realize transverse mode switchable single-frequency fiber laser based on an AIFG. The high order mode single-frequency 1030 nm fiber laser has much potential to find applications in multiplexing system.

With the development of the information age, the transmission rate and transmission capacity of information continue to increase. As a wireless communication method to achieve high bit rate communication, space laser communication plays an increasingly obvious role in global communications. In the current space laser communication system, the optical communication terminal uses a detector to detect the position of the received optical signal, and then the servo mechanism on it performs facula tracking. However, when a four-quadrant detector (4QD) is used to detect optical signal, the received optical signal generally contains three main types of noise, which are background radiation noise, shot noise and thermal noise. These three kinds of noise can be equivalent to Gaussian white noise. In this paper, a single-frequency cosine signal is used to modulate the intensity of the optical signal received by the 4QD, and then the modulated optical signal is detected by a spectrum analysis method based on the cross-correlation algorithm. This method reduces the relative error of the spectral line amplitude when the SNR is -5dB from 2.23% to 0.88%, and reduces the relative error of the spectral line amplitude when the SNR is -20dB from 17.6% to 5.49%. Therefore, this method can well suppress Gaussian white noise and improve the detection accuracy of modulated optical signal under extremely low SNR conditions.

An absolute distance measurement system based on LFSI with an auxiliary interferometer for nonlinearity correction is established. The tunable wavelength range of the laser source is between 1528nm and1568nm. The experimental results shows that the error is within 13μm in the measuring range of 1-10mm. It is found that the distance varies over time with the speed up to 15nm in one scan cycle of laser source, which has not been mentioned in the previous research. In order to solve this problem, the drift of the distance is analyzed, which can guide us to improve the precision of Laser Frequency scanning interferometry method.

Silicon is one of the most important semiconductor materials and the basic material in the field of modern microelectronics, and it has been widely used in microelectronics and photovoltaic industries which are closely related to our daily life. Because the traditional silicon wafer cutting technology has some serious problems such as insufficient cutting accuracy, low efficiency, and serious pollution, the laser processing has been paid more and more attention in silicon wafer cutting applications in about recent fifteen years. Therefore, it is extremely important to develop the laser silicon wafer cutting procedure for the improvement of the laser silicon wafer processing technology. An algorithm named as constrained interpolation profile has been invented in computational fluid dynamics. It is actually a semi-Lagrangian method to solve hyperbolic partial differential equations, and has the advantages of the stable results, compact process, and low dissipation, etc. Focused Gaussian laser beams with the same energy of 200 μJ and pulse widths of 100 fs, 20 ps, and 0.5 ns, respectively, were irradiated on the surface of a silicon wafer. The physical properties of density, temperature, and pressure in both time and space domains were obtained by means of the algorithm of constrained interpolation profile in the laser processing simulation. The mechanisms of laser silicon wafer processing were studied in detail by analyzing the changes in physical properties of silicon material. The conclusions of this paper might be useful in the optimization of a silicon wafer cutting process by the use of a pulsed laser.

This paper reports a no-water-cooling side-pump rod amplifier and has more detailed simulation calculations. Study on the pump light distribution in the rod medium and thermal stress, a nearly flat-top gain distribution and low thermal effect are obtained through design and simulation. The size of rod medium is Φ18×150mm, pump distance is 5mm, there are 15 diode lasers on the side of the rod medium in a spiral staircase arrangement, and the misalignment angle of each laser diode is 24°. This paper provides many references for the no-water-cooling laser system and broadens the application of large-module laser amplifiers.

We introduce a new class of partially coherent beams with non-uniform correlation structure called radially polarized rectangular Hermite non-uniformly correlated (RPRHNUC) beams and study the propagation properties of this kind of beams in free space and atmospheric turbulence. How the mode orders and coherence lengths affect the resistance of such beams to turbulence is also investigated. RPRHNUC beams possess the self-focusing properties. This kind of beams will prove useful in free-space optical communications and other fields.

Aiming at the images of relevant monitored objects in the process of laser cladding, a super resolution algorithm technology was proposed to optimize and enhance the key details of the images, and the enhanced image content was segmented, extracted and counted. First, construct a training of a sub-resolution convolutional neural network (SRCNN) model; the original low resolution is predicted by the weight after training, the image quality evaluation results: peak signal-to-noise ratio (PSNR) is 30.198212, structural similarity (SSIM) is 0.969966; the most based on the maximum entropy dual threshold split algorithm combined with image processing, extracting and statistics on the powder object in the segmentation result image, the number of effective powders and proportion of the original wandering map and the predicted output delay image is [112, 33.6%] and [240, 40.6%]. The research results show that the cladding image output from the original image after the super resolution model has been significantly improved in terms of clarity and quality as well as the optimization and enhancement of the details of the monitored object.

A time-series prediction method for the geometric characteristics (length, length, area) of the molten pool in the laser cladding process is studied. This method uses the historical data of the change of the geometric characteristics of the molten pool to predict the geometric characteristics of the molten pool at the next moment, so as to promote the application in the control of the shape of the molten pool and the estimation of the state of the molten pool. In view of the time correlation shown by the time series of the geometric characteristics of the molten pool, a time series prediction method for the geometric characteristics of the molten pool was developed based on the Autoregressive Integrated Moving Average (ARIMA) model, and the dynamic stability index of the molten pool was proposed. The results show that the area of the molten pool has the best prediction accuracy, and the Mean Absolute Percentage Error (MAPE) is only 3.105, while the predicted MAPE of the width of the molten pool is 3.464 and the length of the predicted MAPE is 4.048. The dynamic stability index proposed can reflect the fluctuation of the molten pool.

In this paper, we established a two-dimensional spatial axisymmetric finite element model to simulate the laser-supported absorption wave (LSAW) induced millisecond-nanosecond (ms-ns) combined-pulse laser (CPL) on silicon, made theoretical investigation. And the finite element analysis software, COMSOL Multiphysics, was utilized in the research. we simulated the propagation procedure of LSAW based on hydrodynamic theory. All the important physical process were considered in the model which were inverse bremsstrahlung, thermal radiation, heat conduction and thermal convection. We simulated silicon irradiated by ms-ns CPL in the case of different pulse delay and ms laser energies, the pulse delay is 1ms, the ns laser energy is 0.1J, the ms laser energy was 3J, 4J, 5J, 6J, respectively. We first obtain the simulation result of velocity fields of LSAW, the results showed that the velocity of LSAW induced by ms-ns CPL decreases with the increasing of ms laser energy. Aiming at obtaining the relationship between the velocity of LSAW, ms laser energies and pulse delay. We keep the ns laser energy density unchanged, the pulse delay was 0, 0.2ms, 0.4ms, 0.6ms, 0.8ms, 1ms, 2ms, 3ms, respectively; the results showed that when the pulse delay is 0.8ms, the ms laser energy is 3J, the velocity of LSAW induced by ms-ns CPL increases obviously. It may be due to the plasma induced by ms laser provides initial electrons for the ns laser ionizing the silicon to produce plasma. The results of the study can be applied in the laser propulsion and laser enhancement technology, etc.

Edge extraction of weld pool image is the key to realize on-line detection and control of laser cladding during the process of industrial laser manufacturing,and the accuracy of on-line control of cladding layer quality is largely determined by the accuracy of extracted weld pool edge.In this paper, a laser cladding pool image detection system based on machine vision is built to collect the molten pool image in the process of laser cladding. According to the characteristics of laser cladding pool image, the image is preprocessed. In this paper, an improved multi-structure, multi-scale and multi-directional morphological operator is proposed to process the molten pool image, and the accuracy and anti-noise ability of different edge detection methods are compared and analyzed. the improved mathematical morphology edge detection method can not only suppress noise but also extract the edge of laser cladding pool image more accurately.

In the laser cladding process, there are a large number of interference factors such as arc light, metal droplets, powder splash, etc., which makes it difficult to extract the edge of the melt pool. Aiming at the problem that it is difficult to extract the edge of melt pool accurately, a method of edge detection of melt pool based on mathematical morphology and Chan-Vese active contour model is proposed in this paper. After median filtering, the binary image of the melt pool is obtained by threshold segmentation. The initial contour of the melt pool is obtained by mathematical morphology connected domain labeling algorithm. On this basis, the connected region contour is taken as the initial contour, and the Chan Vese active contour model is used to extract the edge of the melt pool. The experimental results show that this method can achieve accurate extraction of melt pool edge, and has good anti-interference performance, which provides a good foundation for subsequent melt pool feature extraction and target recognition.

The liquid crystal spatial light modulator is an effective method to change the quality of the laser beam light field distribution, and the phase hologram is the key to the function of the pure phase liquid crystal spatial light modulator. An improved iterative algorithm for beam shaping is proposed, which is improved on the basis of the traditional G-S algorithm. The improved algorithm is more universal, has better rapid convergence and design flexibility. By proposing an optimization factor ζ, the original uneven light intensity distribution in the light field is compensated, and the advantages of the G-S algorithm that the light field is reshaped by the clear boundary are retained and the uniformity of the light field distribution is improved. The experimental results show that the liquid crystal spatial light modulator can improve the nearfield beam quality very well, the energy utilization rate of the shaped output beam is 97%, and its top unevenness is 25.6% .

During the on-orbit operation of space spacecraft, it is easy to be affected by the small vibration from the satellite platform, especially the key sensitive loads carried by the spacecraft. The traditional method is to install a passive damping vibration isolation system between the platform and the sensitive loads. However, the passive vibration isolation system only has a good suppression effect on the high-frequency and large amplitude vibration, and can suppress the low-frequency and large amplitude vibration below 10Hz，the vibration isolation effect in the resonance section is poor. Therefore, in order to solve this problem, an active vibration isolation system of 6-DOF Stewart platform driven by piezoelectric actuator is proposed in this paper. Firstly, the characteristics of Stewart platform are analyzed and modeled, and on this basis, the deformation and displacement of each leg are obtained through decoupling calculation, and each leg is servo controlled with high precision; Secondly, the inherent hysteresis nonlinearity of piezoelectric ceramics has a serious impact on the positioning accuracy. By analyzing the hysteresis mechanism of piezoelectric actuator, a phenomenal hysteresis mathematical model based on Maxwell-Slip operator is established. Finally, the feedforward inverse compensation and feedback linearization methods are proposed, and the system verification test is established. The test results show that, the active and passive vibration isolation system designed in this paper greatly improves the positioning accuracy of piezoelectric actuator and the active vibration isolation performance of the platform.

The research on optical-mechanical system based on additive manufacturing is based on additive manufacturing, diamond turning, high-precision magnetorheological polishing, surface modification technology, internal lattice structure topology optimization and so on. It can overcome the problems of adhesive use and material matching in the traditional structure design, greatly reduce the difficulty of assembly and thermal control, and realize the lightweight design of internal structure that can not be realized by traditional processing methods. In addition, because the mirror body and its supporting structure are made of same metal materials and integrated, the strength and stiffness are greatly improved compared with the traditional design method. This paper summarizes the development status and technical parameters of additive manufacturing opto-mechanical system at home and abroad. The research progress of surface modification technology by domestic and foreign scholars was focused and the post-processing process and core technologies of the optical-mechanical system were described.

In this paper, discuss about thermal damage of Kevlar composites in laser processing.Kevlar fiber is a unique aramid fiber with excellent physical properties unique to aramid fiber, such as high wear resistance and high tear resistance. It is precisely because of these excellent physical properties that common traditional mechanical tool processing methods are not effective, such as tool wear, fiber breakage, and material plate chipping. In the corresponding research at home and abroad, laser processing is considered to be a more excellent processing technology, which can overcome various processing difficulties caused by physical strength, but due to the thermal effect of laser processing, it will cause the heated area of the cut part Produce combustion, increase brittleness, and affect processing results. Therefore, studying the temperature and stress effects of lasers on Kevlar composites under different powers is the key to improving processing technology. This paper mainly studies the damage of Kevlar composites with the same thickness during laser irradiation, monitors the irradiation temperature, and uses an automatic three-dimensional surface measuring instrument to obtain photomicrographs of the damaged parts. In the experiment, a suitable experimental device was established to use a 1064nm laser to output a continuous laser to irradiate the Kevlar composite target material and monitor the real-time temperature at the same time

The photoelectric detector is a very significance part in laser and its application system, but when photoelectric detector irradiated by high energy laser, the laser may cause thermal damage to the photoelectric detector, when the temperature more than its melting point and vaporization point ,there will be a permanent damage in PIN photodetector, leading to the failure of photoelectric detector. In order to study the photodiode damage mechanism by 1064nm CW laser irradiation, a set of experimental system has been built, choosing appropriate laser power parameters to irradiate silicon-based PIN photodiode and monitoring the surface temperature in the process of irradiation, until the PIN photodiode complete failure. The measurement results of real-time temperature, dark current change and damage morphology were analyzed to conclude the failure reason of the PIN photodiode. The results show that with the increase of laser power, the surface temperature of PIN photodiode also increases, and the damage area increases gradually. Before laser irradiation, the initial dark current of PIN photodiode is the same.

With the rapid development of the times, traditional communication methods such as microwave communication have been difficult to meet the needs of high-speed and high-capacity communication. People begin to look for new communication technologies to replace the existing communication methods. Laser communication has the advantages of high bandwidth, small terminal volume and good security. In the process of space laser communication, the coupling of space light to single-mode fiber is one of the difficulties. In the process of practical application, external jitter (atmospheric turbulence, platform vibration, etc.) makes the focus spot offset from the end face of the optical fiber, greatly reduces the energy coupled into the single-mode optical fiber, and seriously affects the communication quality. Applying the mature optical fiber communication technology to space laser communication can not only improve the transmission rate of the link, but also improve the communication quality and simplify the system composition. Based on laser nutation, aiming at the problem of space optical coupling into single-mode fiber in space laser communication, this paper analyzes the influence of alignment error on coupling efficiency. The lateral deviation has the greatest influence. In this paper, a laser nutation coupling system model based on the fast mirror is built. The model is based on the principle of mode field matching. The nutation signal of the nutation fast mirror is used as the modulation signal, and the optical power output by the photodetector is used as the feedback for calculation. The fast mirror is controlled in real time to compensate the transverse deviation. The algorithm flow of laser nutation is described, the simulation model is built, and the feasibility of the algorithm is verified. Based on different algorithm parameters such as nutation radius and convergence step, the relationship between parameter value and algorithm performance is obtained.

Potassium dihydrogen phosphate crystal has many advantages, such as higher linear photoelectric coefficient, lower half-wave voltage, wider transmittance band, excellent optical uniformity and the ability to grow into large size crystal, so it is the only nonlinear crystal material that can be used in inertial confinement fusion engineering. However, in practical application, the actual damage threshold of such optical components is far lower than the theoretical damage threshold, and the damage is serious when the ultraviolet laser is irradiated, components.An in-depth study of the characteristics of microdefects and their changes in physical structure and chemical properties under irradiation environment is helpful to understand the mechanism of crystal irradiation damage and improve the damage characteristics of KDP crystal. Considering that different growth processes of KDP crystals lead to different internal defects, the types of defects that determine the damage threshold may also be different. Therefore, this in the present work, based on HSE06 and PBE0 functional, the Sr²⁺，Fe³⁺ at the domestic application of KDP crystal materials, and studies the evolution characteristics of material body defects under high-energy particle irradiation by acquiring the basic characteristics of radiation damage. The research results will provide reference for the development and application of high-power laser devices. First principles calculation method was used to study the defects of Sr²⁺ metal impurity in KDP crystal and its effect on crystal light absorption performance. Considering the influence of electron exchange correlation potential on the crystal structure and the accuracy of electronic properties, the cell parameters and electronic properties of KDP crystal were calculated by using HSE06 and PBE0 functional respectively.

Femtosecond laser has the characteristics of short pulse width and high peak power and is widely used in laser micromachining，optical communication, medical applications and other fields. Compared with infrared lasers, ultraviolet lasers have shorter wavelength and higher single-photon energy, which makes the processing heat affected area smaller and can perform precise processing on special materials. With the advancement of science and technology, people are demanding higher precision in laser processing, then ultrashort pulse lasers in the ultraviolet spectrum have gradually came into people's sight. At present, there have been many reports on femtosecond solid-state ultraviolet lasers domestic and overseas. However, solid-state lasers are bulky and difficult to dissipate heat. In contrast, the fiber femtosecond laser has a stable and compact structure and is more suitable for industrial processing. However, it is understood that there are very few domestic studies on femtosecond fiber lasers in the ultraviolet band. In recent years, fiber laser technology has been greatly developed. Femtosecond fiber lasers have good beam quality and high laser directivity, besides it can provide high-power, high-repetition output in the near-infrared spectrum. In this experiment, we propose an ultraviolet femtosecond laser system based on β-BaB₂O₄ crystal. The fundamental frequency laser passes through two BBO crystals to generate second harmonic generation and third harmonic generation. At the same time, we adjust the angle at which each beam of laser passes through each crystal to meet the conditions of phase matching and obtain the maximum conversion efficiency. It’s worth mentioning that the system has a compact structure, low cost, and high conversion efficiency. Besides, it has broad application prospects.

We demonstrate and compare the absorption spectra, laser performance and thermal lens effect of a-, b-, and c-cut 15 at% Er:YAP crystal in detail. The Er:YAP crystal along a-axis possesses larger absorption coefficient, but the b- axis Er:YAP crystal exhibits better laser performance. A maximum output power of 916 mW is achieved in the b-axis Er:YAP crystal with slope efficiency of 16.0%. As the important factors that affecting the laser performance of solid-state laser, the thermal lens effect of Er:YAP crystal is studied by simulate the temperature distributions and the thermally induced focal lengths. The result indicates that the b-cut Er:YAP crystal has a weaker thermal lens effect due to its high thermal conductivity and low temperature refractive index coefficient. All the result indicate that the b-cut Er:YAP crystal shows a better laser performance, which is a promising candidate for high performance CW mid-infrared laser.

This paper introduces a simulation system for laser remote ranging. The device provides a simulation range of more than 300km, which can realize multiple echo pulses and conduct the test of the verification period maximum range of the remote ranging algorithm. The device accuracy simulates the distance up to 150m, error of 0.9m. The width of the echo pulse can vary depending on the transmission distance and the target characteristics. Considering the simulated distance measurement of the dynamic target, the change of the echo pulse return moment corresponds to the target movement speed, the ranging algorithm of the dynamic target can be verified.

In this paper, several test methods provided in this standard are analyzed, and the influence of the attenuation amount introduced in the test process on the test results of laser divergence angle is analyzed. Considering the test error introduced by attenuation, a method to eliminate this error is proposed, which provides the basis for accurate measurement of divergence angle.

Laser processing is a technique based on the interaction between a laser and the substance for cutting, drilling, cleaning, welding, and other operations on metallic or non-metallic materials. It is widely used in some important fields of the national economy such as automobiles, microelectronics, electrical appliances, aviation, metallurgy, medical treatment, and machinery manufacturing. In the process of high-powered laser processing, a large amount of plasma will be generated and there will be the obvious inverse Bremsstrahlung absorption (IBA) near the plasma plume. The effect of laser processing will be significantly deteriorated due to the absorption of laser photons and changes in light intensity distribution. Besides, laser-induced plasma is produced during the interaction between a high-powered laser and materials. Also, it has the very important value in the research of analyzing the high-powered laser processing. To fully understand the laserinduced plasma, this paper uses the Hilbert procedure to numerically investigate the plasma generated in the laser processing. The method firstly acquires the images corresponding to the fringes of a Mach–Zehnder interferometer by using the detection after a probe laser beam passing through the plasma plume. Then, a series of operations such as the spectrum shift, unwrap, and Abel inverse transformation are performed after a fast Fourier transform (FFT). Finally, the density distribution of plasma can be calculated. This methodology provides a new algorithm for the research of laserinduced plasma, and it also valuable for the understanding the high-powered laser processing process.

In this paper, a simulation model is established to study the temperature rises of the rust layer surface and the metal substrate surface when the continuous laser and nanosecond laser act on the rust layer surface, and draw the temperature charts of the rust layer surface and the metal substrate surface, so as to analyze the temperature rising process of laser cleaning rusty steel plate. The temperature rising process of the rust layer surface and the metal substrate was studied. The simulation results show that: when the continuous laser power is 239W, the peak temperature of the rust layer surface is 1772.1K. At this time, the temperature of the rust layer surface is close to the melting point, but the temperature of the substrate surface has no significant rise. When the power of nanosecond pulse is 5135kW, the peak temperature of the rust layer surface is 1772.8K. At this time, the surface temperature of the rust layer is close to the melting point, but the substrate surface temperature has no significant rise. The results of this paper not only provide a theoretical basis for laser cleaning of rusty steel plate, but also provide a theoretical support for the application of laser cleaning technology.

Ideally, lasers follow Beer-Lambert's law when travel through the atmosphere. Beer-Lambert’s law is premised on single scattering. However, in the actual atmospheric environment a variety of circumstances will cause the deviation of Beer-Lambert’s law. In this study, a simulation model of laser atmospheric transmission is established based on the Monte Carlo method. The established simulation model is from the perspective of each photon. The random motion of photons is simulated, that is to say, the radiation transport equation is not involved. In simulation model, migration direction and migration distance of photons are determined by the sampling theory of Monte Carlo on the probability distribution of photons scattering angle and free path. Migration direction is determined by the scattering phase function. Migration distance is related with the extinction coefficient. The energy change caused by scattering is determined by the single scattering albedo(abs). For a photon, if its energy is absorbed to zero before it reaches at the detector, calculation of this photon transmission process would be end up. Whether a photon is received by the detector can be judged by observing whether the motion track of the photon intersects with the detection region. Thus, by tracking motion track of each photon of the laser beam, the transmission of the laser can be obtained. In this study, several key factors of laser transmittance in the atmosphere such as extinction coefficient, ratio of scattered light, and absorption are carefully studied by the established simulation model.

Herein, we report a one-step laser writing method to form porous graphene on polyimide (PI), which is capable of broadband-spectral detection. By controlling different parameters of laser processed patterns, various samples were obtained. The comparative photoresponsivity and photocurrent curves of each porous graphene sample were obtained by conducting photoelectric testing at wavelength of 625 nm. The highest photoresponsivity obtained is 5.6´10^-4 A/W, and the corresponding response and recovery times are 27 and 30 s. The method provides a new route to the fabrication of graphene photodetectors and promotes the development of future applications of optoelectronic devices in wearable and flexible electronics.

We propose a thin-disk multi-pass amplifier based on a pair of conjugated parabolic mirrors. Pumped with 940nm laser diode and seeded with 1030nm ps regenerative amplifier, this novel amplifier scheme exhibits relatively high efficiency and insensitivity to the thermal lensing of the thin-disk caused by high pump power density. Parameters of the output beam have been measured. The beam quality of the seed laser was found to be deteriorated after propagating through the amplifier, with the M2 factor changed from 1.3 to 18.4. In order to acquire a further comprehension on the origins of the deterioration of beam quality, simulations and experiments were carried out.

A functional flexible photonics-assisted frequency measurement (PFM) based on polarization multiplexing and coarse/accurate (C/A) compensation is proposed. Under the same system configuration, it can support fast frequency measuring with moderate accuracy (<0.2 GHz) and wideband range (1 GHz-31 GHz) for radar warning receiver (RWR) using a Mach-Zehnder interferometer (MZI). Moreover, based on the coarse measurement result, a more accurate frequency measurement can be given for electronic countermeasures receiver (ECMR). It is implemented by stimulated Brillouin scattering and improves the accuracy to 20 MHz. Especially, the electro-optic (E/O) modulation section is performed with the assistance of polarization multiplexing, which improves the stability and simplifies the system.

In order to study the damage area and morphology of silicon-based APD under different power density and different action time laser irradiation, based on two-dimensional microscopic measurement technology, the damage area and morphology of silicon-based APD were measured with laser power density and action time. The change. The results show that the damage area gradually increases with the increase of laser power density; with the increase of power density, APD produces surface peeling, wrinkles, cracks, pits and other damage effects.

Recently, it has been reported, through using an in-situ laser exposure, nano holed structures can be created on the GaAs surface that is pre-capped by a thin InAs wetting layer and such nano holes were further proven to well serve as the preferential nucleation sites of InAs quantum dots (QDs). In this paper, we presented a study of how to further modify the morphology of the nano holes. First homo-deposition of 500nm GaAs buffer layer on GaAs (100) substrate and after capping of 0.5ML InAs, the as-prepared surface was in-situ exposed by a laser shot with energy of 20mJ. Then four different samples (A-D) were prepared, respectively corresponding to directly finishing the growth for sample A, for sample B repeating one cycle of “0.3ML InAs wetting layer capping + in situ laser exposure” before finishing the whole growth, two cycles for sample C and three cycles for sample D. It is found the density of nano holes on sample A is merely 5.5×10⁸/cm² with relatively small size possessing an average depth and width at 0.9nm and 36.6nm. After one cycle of “0.3ML InAs wetting layer capping + in situ laser exposure”, the density of nano holes on sample B increases by nearly one order of magnitude to 4.33×10⁹/cm² and the average depth and width become 1.0nm and 44.6nm. Further after two and three cycles, the resulting density would rise to 8.53 × 10⁹/cm² (sample C) and 1.12 × 10¹⁰/cm² (sample D), correspondingly, the average depth/width are magnified to 1.1nm/54.2nm and 1.3nm/59.7nm. Hence, we have demonstrated an effective approach to modify the in-situ laser nano-holed patterning of GaAs surface which is supposed to have promising applications in controlled growth of QDs.

The laser transceiver contains a lot of complex optical refractors. The laser signal is emitted from the laser, transmitted through the optical fiber and the transceiver, and entered into the air after multiple splitting, reflection and expansion, so as to exchange information with the outside world. The direction of the laser axis changes with the motion of the two-dimensional turntable. In the process of coupling between the laser fiber and the transceiver, the parallel light generated by the receiving and transmitting collimator should be meet the requirements of consistent divergence angel, parallelism and coincidence at the light outlet of the device. In this paper, the method optical axis consistency detection and adjustment in the process of laser coupling and turntable integration is studied, the device for determining the optical axis reference is designed. By means of precise adjustment, the optical axis and the reference device coincide precisely, and the detection and debugging of optical axis paralleling and coincidence are realized.

In this article, the finite element simulation software is used to analyze the temperature change and the removal depth of the nanosecond continuous laser to remove rubber tracks from the airport runway. The simulation results show that as the continuous laser output energy in nanoseconds increases, the removal depth gradually increases and the temperature of the laser action point gradually increases, so that the glue layer peels off. of the base surface without damaging the base. is removed when nanosecond power is 200W and 150W. Depth is best. In terms of laser glue removal simulation research, the distribution of the temperature field of the glue layer under the action of a pulsed Gaussian heat source is simulated to obtain a better vaporization temperature. Among combined lasers, continuous lasers have better thermal conduction and surface heating effects, but the depth of withdrawal is worse than nanosecond lasers. The nanosecond laser has a better effect of removing mechanical vibration, the central idea of the proposed combined laser is to use high-power short-pulse lasers to quickly increase the target surface temperature, and then according to the positive correlation between material absorption rate and temperature, it can change the material surface to follow. The continuous laser energy absorption characteristics improve the coupling efficiency of the material to laser energy and achieve the expected elimination goal.

In this paper, aiming at high-end stainless steel subway products, a new product of stainless steel rail vehicles manufactured by using thin plate lap laser welding instead of resistance spot welding was first developed in China, which made the stainless steel car body structure more optimized, and the welding quality and manufacturing process of its car body steel structure were significantly improved, and advanced stainless steel vehicles entered the high-end vehicle market. Therefore, this paper develops the laser welding process of stainless steel car body, optimizes the process parameters, defines the weld quality standard and develops the weld quality monitoring device, builds the laser welding manufacturing system, and realizes the batch application of the new laser welding technology in high-end stainless steel rail vehicle products. At present, it has formed the world's leading batch production capacity of high-end stainless steel vehicle products and improved the competitiveness of the company at home and abroad.