This PDF file contains the front matter associated with SPIE Proceedings Volume 12501, including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

Concerning future ultra wideband (UWB) real-time measurement of electromagnetic spectrum demand in electromagnetic battlefield, this paper proposes a frequency-time mapping measurement method based on microwave photonics. Frequency-time mapping, or real-time Fourier transform, maps the input ultra-wideband electromagnetic spectrum information to the output time-domain waveform. The electromagnetic spectrum signal is modulated to light by CS-SSB modulation, and frequency-time mapping is formed by using electrically modulated micro-ring. Through simulation verification, the method can achieve frequency measurement of panoramic bandwidth signal from100MHz to 30GHz.The frequency resolution can reach 80 MHZ, whose scanning time is less than 20us. The method can achieve ultra-high speed, high-precision, broadband measurement of wideband complex electromagnetic spectrum situation, providing technical support for future electromagnetic spectrum operations.

In this study, the visible light spectroscopy was used to achieve the sweetness quantitative measurement of apple. In the experiments, the absorption spectra of apple samples in total of 100 groups were obtained in the waveband from 400-800nm with interval of 5nm by using the visible light spectroscopy. At the same time, the real sweetness values of all apples were measured by using a commercial fruit sugar meter. To achieve the sweetness quantitative spectral measurement, the back propagation (BP) neural network was used to supervised train the absorption spectral for 80 groups of training samples, and 20 groups of apples were utilized as the test samples. The effects of neuron numbers in the hidden layer, learning rate factor and the training times on the root-mean-square error (RMSE) of sweetness were investigated. Under the optimal parameters of BP neural network, the RMSE of sweetness for the test apple samples can reach 0.12218%, which is superior to that of the commercial fruit sugar meter (0.2%). Compared with the correlation coefficients for the training samples and test samples based on the partial least square (PLS) algorithm, it can be demonstrated that the visible light spectroscopy combined with BP neural network has the potential superiority and application value in the sweetness quantitative spectral measurement of fruit.

A novel insertable monolithic ring laser based on a Nd:YAG-YAG bonded crystal was proposed for high output power single-frequency operation. In a proof-of-principle experiment, the unidirectional resonator pumped by an 808 nm diode laser was constructed with a half-wave plate and a TGG etalon, thus achieving both structural stability and functional tunability. A single-frequency laser with the output power of 4.1 W is obtained at 1064 nm, corresponding to the slope efficiency of 17.7 % and an optical-to-optical efficiency of 11.8 %. The power fluctuation is measured to be within ±1% over 20 min. The average beam quality factor M2 is measured to be 2.07.

The problem of insignificant image features and poor image quality in the acquisition of terahertz spectral images of unsound wheat. Therefore, this study proposed the FFDNet-VGG terahertz image enhancement algorithm based on the FFDNet denoising algorithm and VGG feature extraction algorithm. The experimental results showed that this algorithm could effectively improve the image quality compared with the traditional algorithms such as BM3D and WNNM, and the PSNR and SSIM of the enhanced images were 39.10 dB and 0.93, respectively. The wheat unsound grain images processed by FFDNet, VGG and FFDNet-VGG algorithms were verified by CNN classification network with the classification accuracy of 93.1% and 93.7%, respectively. FFDNet-VGG effectively enhances the wheat unsound grain terahertz spectral images.

With the increasing application of titanium alloys (Ti-6Al-4V) in aero engineering, great challenges have been posed to improve the surface quality and machining accuracy of titanium alloy. Titanium alloy is difficult to be processed. The existing processes suffer from thermal damage or low-efficiency. In this paper, laser and shaped tube electrochemical machining (Laser-STEM) has been employ to process titanium alloy, in which both the laser beam and electrolyte jet are guided to the machining zone through the inner hole of a specially designed tubular electrode. The processing characteristics of TC4 titanium under different processing voltages, laser power, and feeding rates were experimentally studied, while using sodium nitrate as the electrolyte. Influences of key process parameters on the machining profile size and surface roughness was explored. Results showed that the deep and narrow grooves with a good surface profile can be obtained under the voltage of about 20 V, laser power of 3 W, and electrode feeding rate of 1.8 mm/min. Finally, the rectangular wave slot with an average width of 1.6 mm and depth of 0.759 mm was machined by a layer-by-layer laser and electrochemical machining method. The feasibility of laser and shaped tube electrochemical hybrid machining of TC4 titanium alloy with high precision and efficiency has been verified, which laid a foundation for the application of this process in aerospace manufacturing.

The analytical equations of the polychromatic stochastic electromagnetic multi-Gaussian Schell-model vortex (EMGSMV) beam through oceanic turbulence are obtained in theory. The influences of source parameters and turbulence on changes in spectral shifts and polarization of a polychromatic EMGSMV beam are numerically analyzed. It is seen that the relative spectral shift of such beam with larger N , smaller l and smaller δ₀ will evolve from red shift to blue shift on propagation, and the polarization can become poor when a polychromatic EMGSMV beam propagates in stronger oceanic turbulence.

Due to the characteristics of high hardness, wear resistance, corrosion resistance, excellent thermal shock resistance, and low thermal expansion coefficient, Si₃N₄ ceramics are widely used in aerospace, national defense, electronic and electrical, mechanical, chemical, and other fields. In this paper, the grooving experiments of Si₃N₄ ceramics were carried out by using a novel dual-beam coupled nanosecond pulse laser, and the influence of laser power and scanning speed on the surface morphology and geometric size of grooves were studied. The results show that the laser power has a significant effect on the surface morphology and geometric size of grooves. With the increase of laser power, the laser power density augments, and the width and depth of grooves increase. The groove width and groove depth first increase and then decrease with the increase of scanning speed, and both the groove width and depth reach the maximum value at scanning speed of 800 mm/min.

Nickel-based superalloy (DZ411) is widely used in the manufacture of high-temperature components in the aerospace field due to its excellent physical and mechanical properties, such as high-temperature resistance, oxidation resistance, and corrosion resistance. Laser polishing can improve the surface quality and service performance of nickel-based superalloy materials. In this paper, a new type of multi-beam coupling laser based conventional laser is used to process the nickelbased superalloy materials. The processing experiments of nickel-based superalloy were carried out by changing laser power, scanning speed, and scanning pitch. Then the polished surfaces were observed and detected by laser confocal microscope. The results show that the surface of nickel-based superalloy materials has certain regularity with the variations of process parameters. Under these experimental parameters, surface roughness (Ra) decreases first and then increases with the increase of laser power, scanning speed, and scanning pitch. The minimum Ra of the polished surface is 1.06 μm under the process parameter combinations of laser power of 1W, scanning speed of 400 mm/s, and scanning pitch of 20 μm. The maximum valley depth (Rv) and the maximum height (Rz) of profile first decrease and then increase with the increase of laser power or scanning speed. However, Rv and Rz had a little rate of fluctuation with the increase of scanning pitch. The laser polishing process involves the dynamic time-varying absorption mechanism of the coupled laser energy by polymorphic materials, and it is accompanied by complex physical processes such as material melting, gasification, and re-condensation. When Ra is relatively low, a clear corrugated structure appears on the machined surface. This research work can provide process data support for optimizing the polishing process parameters of nickel-based superalloys and expand the laser processing types.

With the rapid development of advanced manufacturing technology, the market demand for high-precision functional curved surface parts is increasing. The traditional processing technology has shortcomings in the precision forming of curved parts, especially in the processing of functional and fine structures. Laser processing has the characteristics of non-contact, high precision, and controllable energy, which makes it have special advantages in machining highperformance surfaces. This paper analyzed the application requirements of high-precision complex surface processing and the differences between traditional surface processing methods and curved surface laser processing. A five-axis CNC laser processing technology for curved surfaces was proposed. At the same time, the digital modeling and laser machining simulation verification of a typical curved surface part were carried out by using this processing technology. The result proves the effectiveness of the digital processing flow of curved surface laser machining and provides a digital solution for laser machining of high-precision and complex curved surfaces.

Computational holography is one of the most potential 3D display technologies. In recent years, with the continuous iterative evolution of holographic optical theory and the continuous maturity of computer software and hardware technologies, related technologies have developed rapidly. Correlation optimization algorithm is a research hotspot at present. This paper studies and analyzes several pure phase hologram generation and optimization algorithms commonly used in this field in recent years, and points out that the above algorithms have the limitation that the quality of reconstructed images cannot be further effectively improved; for this problem, we propose a new optimization idea based on high-dimensional space is to find the reconstructed image with similar pixel distribution to the target image in the highdimensional space. At the same time, we propose a more practical pixel correction method, which considers the reconstruction of the image from the high-dimensional space. Optimization can further effectively reduce interference such as speckle noise and improve the quality of reconstructed images. Through experimental calculation, we obtained the peak signal-to-noise ratio and structural similarity of the reconstructed image before and after the correction of the common algorithm and the original image and compared them. It can be verified through experiments that the numerical improvement of the above two indicators obtained by our proposed method is obvious. The quality of the reconstructed images has also been better improved.

Laser and shaped tube electrochemical machining (Laser-STEM) has been proposed to process small holes with high efficiency and surface quality. In Laser-STEM the laser energy is transmitted to the machining zone with high efficiency by total internal reflection confined in the inner hole of the tool electrode. Coupling between the laser and the tool electrode is of importance to guarantee the stability and accuracy of the Laser-STEM process. The previous studied focuses the laser beam to the entrance of the tool electrode utilizing a focusing lens. However, the method was easily affected by the focal length, spot size, and installation error, which would influence laser coupling stability and transmission efficiency. This paper focuses on the research of a novel laser coupling method based on the conical optical guide to improve the coupling robustness. Mathematical model of the laser propagation through the conical guide has been derived. The maximum coupling angle of the conical guide with different sizes was obtained. The effect of laserliquid- core fiber tool electrode coupling error on laser energy coupling efficiency is investigated by optical simulation, and the feasibility of conical light-guiding devices for efficient conduction of laser energy was verified experimentally. Results showed that the conical optical guide could improve the laser axial incidence range by about 3 times, the radial range by 2 times, and the angular coupling range by 1.9 times, with the laser coupling efficiency of 90%. The introduction of the conical guide remarkably improved the coupling efficiency and stability of the laser and tool electrode, which is of great significance for improving the stability of Laser-STEM.

We propose and demonstrate a simple method to generate an all-fiber high-order transverse-mode switchable laser using a few-mode Bragg fiber grating (FM-FBG). The switchable output of the LP₀₂ mode, LP₁₁ mode, and LP₀₁ modes is precisely realized by adjusting the operating wavelength in the cavity, which breaks through the limitation of only two low-order modes in most reports about all-fiber transverse-mode switchable lasers. The slope efficiencies for the three modes are 2.5%, 5.9%, and 9.3%, respectively. The central wavelengths of the lasers are 1530.2 nm, 1531.3 nm, and 1532.1 nm, respectively, and the corresponding side mode suppression ratios are -61 dB, -67 dB, and -65 dB, which ensures the purity of the modes. This work has huge potential applications in sensing, mode division multiplexing, optical communication, laser processing, and surface plasmon excitation.

TC4 (Ti-6Al-4V) is a comprehensive metal material with excellent ductility, low density, high specific strength, and a series of advantages such as excellent toughness and weldability, so it is widely used in the aerospace industry. Due to defects such as porosity in the welding process and exposure to alternating loads, welded components of titanium alloys in the aerospace industry become the most vulnerable parts and are extremely susceptible to failure and fracture. In this paper, a single-sided sequential laser impact strengthening process is used to treating the laser welds of TC4 titanium alloy cold rolled parts to investigating the tensile properties of the laser welded welds before and after the process. By observing the tensile fracture by SEM, measuring the microhardness by Vickers hardness tester, and measuring the physical phase by XRD diffractometer, the results of these data were combined to analyze the strengthening mechanism of this laser shock peening process on the laser welds of TC4 titanium alloy. The experimental results show that after the surface strengthening process, the tensile strength and surface hardness of TC4 laser welds are improved compared with those before ¹the treatment. The analysis shows that the high residual compressive stress layer and grain refinement caused by laser shock peening are the reasons for the improvement of mechanical properties of materials.

We propose and demonstrate a method to generate and detect high-order Poincaré sphere beams. By adjusting the input homogeneous polarization states, arbitrary high-order Poincaré sphere beams are obtained. A one-to-one correspondence between the traditional Poincaré sphere beams and high-order Poincaré sphere beams is represented. The generation and detection of the high-order Poincaré sphere beams are realized simultaneously. Our research is helpful to deepen the understanding of the polarization states of light beams and provide useful ideas for the handling of optical experiments.

Monocrystal sapphire have excellent properties such as high strength, hard and brittle, high temperature resistance, chemical corrosion resistance, wear resistance and good infrared transmittance, which are widely used in semiconductor, defense, aerospace and other frontier fields. As a typical hard and brittle material, sapphire has become an obstacle to the development of its application for ultra-precision machining with high efficiency and low damage. Therefore, a suitable method is needed to achieve ultra-precision processing of monocrystal sapphire. Different from traditional machining, laser polishing technology has the characteristics of non-contact processing and no mechanical processing stress, while femtosecond laser processing technology has the advantages of cold processing and no selectivity to the material, so it is suitable for surface polishing of sapphire. In this article, the influence of the femtosecond laser with the center wavelength of 515 nm on the surface polishing of sapphire under different processing modes, scanning interval and scanning speed was studied. By adjusting the laser parameters, the surface roughness of single crystal sapphire was reduced from 1.58 μm to less than 0.3 μm by femtosecond laser polishing.

The spectral range of the optical frequency comb (OFC) generated by electro-optic modulators (EOMs) is limited by the modulation depth. In this paper, an on-chip system based on a Si₃N₄ waveguide is built to broaden a 12.5 GHz electrooptic comb (EO-comb). A numerical simulation is carried out to demonstrate the nonlinearities of self-phase modulation (SPM), Raman soliton self-frequency shift, and dispersive wave generation dominating the spectral broadening of the EO-comb in the waveguide.

As a high-precision detection technique of surface topography based on the interference theory of light, Phase-Shifting Interferometric is susceptible to vibration from the surrounding environment, which reduces the detection accuracy. In order to reduce the influence of vibration errors and improve the phase demodulation accuracy of measured wavefront, an anti-vibration phase demodulation method applied to Phase-Shifting Interferometric is proposed in this paper. This method first acquires two sequences of interference images with phase shifts of 0 and 𝜋𝜋/2 respectively, uses a digital image stabilization algorithm to suppress the vibration error of each frame in the sequence, and synthesizes two frames of interference images with phase shifts of 0 and 𝜋𝜋/2, respectively. Then, based on these two frames of synthesized images with determined phase shifts, the gradient algorithm and the Schmidt Orthogonal Transform are used for wavefront phase demodulation. The experimental results show that the percentage of pixels demodulated effectively at the truncated interface is more than 90%. Compared with the traditional demodulation method, the number of pixels demodulated effectively (demodulation accuracy) is improved.

In this paper, a phase denoised digital speckle pattern interferometry (DSPI) method based on improved variational mode decomposition (IVMD) is proposed to reduce the noise interference in DSPI phase maps. The first step is to decompose the DSPI phase map using the IVMD method and obtain the optimal mode components. Then, an adaptively mode threshold method is proposed for processing the mode components based on the characteristics of the mode components. To obtain the denoised DSPI phase map, the denoised mode components are reconstructed. The results demonstrate that the proposed method is effective in filtering out noise interference and the peak signal-to-noise ratio (PSNR) is higher than that of other denoised methods.

High borosilicate glass has the advantages of high light transmittance, good mechanical performance, chemical stability and thermal stability. It is widely used in daily use, chemistry, architecture, electronics, instruments and other fields. There is a large number of identification requirements in the application. In this paper, based on the 532nm wavelength laser, the marking process of high borosilicate glass is studied. The influence rule and mechanism of duty ratio, repetition frequency, marking speed and defocus amount on the marking effect are explored by single factor control variable method. The research results show that the four process parameters have an important impact on the integrity of the identification profile. Through the optimization of the process parameters, the process window of 532nm wavelength laser identification of high borosilicate glass is obtained, which realizes the good identification effect of the identification morphology and provides a reference for the green light identification of high borosilicate glass.

As a pump source for Ti: Sapphire solid-state lasers, the fiber-coupled green diode laser module is critical. However, existing study findings are insufficient to meet the demands of high brightness diode laser pump sources. In this paper, a high brightness green diode laser fiber-coupled system based on TO-can diode lasers is designed. The FACs are installed within the TO-can diode lasers. The optical step as the spatial beam combining system is made up of the HR mirror and the optical wedge. We discussed the relationship between the reflected beam deflection angle and the optical wedge surface inclination angle under the condition of different HR mirror inclination angles. After that, a strategy with appropriate heat dissipation effect is obtained through thermal simulation. Finally, the simulation results verify that couple 18 TO-can single emitters into a 50μm core diameter and 0.22 numerical aperture optical fiber with an output power of 16.9W, the fiber coupling efficiency is 98%. The brightness is 5.66 MW/(cm²·Sr) and the module dimension is L 220mm×W 80mm×H 45mm.

In order to improve the surface friction properties of 7075 aluminum alloy, micro textures with different morphology and spacing were processed on the surface of 7075 aluminum alloy by femtosecond laser. The size and morphology of laser processing texture were tested by laser confocal microscope, and the parameters of laser processing micro texture were optimized. The results show that due to the different characteristics of oxide layer and internal material on the surface of aluminum alloy, micro texture morphology cannot be processed on the surface when the single pulse energy is too small; When the single pulse energy is too large, the texture depth is too large, which will affect the lubrication and drag reduction performance. The GF-I reciprocating friction and wear tester was used for friction and wear test to explore the area ratio of the optimal drag reduction performance of each micro texture under the load of 0.07m/s and 40n. The experimental results show that the friction coefficient is the smallest when the area ratio of each micro texture morphology is about 8%. In the regular hexagon, the micro texture spacing is 400 μm has the best drag reduction effect, and the drag reduction rate is 36.76% compared with the non textured surface.

An analogue of electromagnetically induced transparency (EIT) in terahertz range with an all-dielectric metasurface is investigated numerically. The unit cell of the silicon-based metasurface is composed of a ring and a rectangular bar. It is found that due to the interaction between the dark mode and the bright mode supported by the ring and the bar, respectively, EIT-like resonance can be realized in this structure. By choosing proper geometrical parameters, the sharp EIT-like transmission peak can be always observed with transmittance higher than 99% and highest Q-factor about 1890. With this high quality EIT resonance, the figure-of-merit for the refractive index sensing of this metasurface is about 260, which is larger the previous reported metal-based metasurfaces. The transmittance property of the EIT-like resonance can be manipulated by changing the structure parameters. This high quality EIT metasurface has great applications in the design of slow-light low-loss equipment, optical modulations, and optical sensing.

Integrating active distributed feedback reflector monolithically to replace HR coating may help reduce the cost of chip fabrication. We present the design and fabrication of a SOA integrated electro-absorption DFB laser based on identical epitaxial layer with HR coating replaced by ADR. The optimized laser structure has a 100-μm ADR, a 160-μm DFB, a 100-μm EAM and a 250-μm SOA. The fabricated device has a threshold current around 40 mA with good single mode stability. With injection current from 40 mA to 100 mA in DFB region, the SMSR is all over 50 dB. The extinction ratio is over -20 dB at the maximum EA bias voltage of 4V. The 10Gb/s eye diagrams for BTB configuration achieve a dynamic extinction over 10 dB and SNR over 7 dB.

In this paper, the preparation and spectral properties of large mode field double-clad (LMA) fiber two-dimensional fiber gratings are studied. Firstly, a new compact grating analysis model for writing fiber gratings with different periods in different regions of the fiber core is theoretically proposed, and the spectral characteristics of the gratings written in different regions of the fiber core are studied based on the transfer matrix method. A three-wavelength two-dimensional fiber grating with a designed wavelength interval of 1.57 nm was successfully fabricated using a 248 nm excimer laser in a large mode field double-clad fiber laser. The research results show that the spectral characteristics of the two-dimensional fiber grating can be changed flexibly by changing the masking parameters, and the structure is compact. The experimentally obtained two-dimensional fiber grating spectrum is consistent with the theoretical analysis. The research results provide a theoretical reference for the design, fabrication and application of two-dimensional fiber gratings.

We reported a mid-infrared intra-cavity ZnGeP₂ optical parametric oscillator (ZGP OPO) pumped by an acousto-optic (AO) Q-switched Ho:YAG oscillator. The 1908nm laser with an output power of 20W was used as the pump source of the Ho:YAG AO Q-switched oscillator. ZGP OPO was placed inside the Ho:YAG oscillator. Under the Q-switched repetition frequency of 5kHz, the maximum output power of the mid-infrared laser was 1.5W. The optical-optical conversion efficiency of the 1908nm laser to the mid-infrared laser was 7.5%, and the slope efficiency was 15%. The two central wavelengths of mid-infrared laser were located at 3.9~4.05μm and 4.35~4.5μm respectively. The pulse width was 29.9ns and the single-pulse energy was 0.3mJ.

Conventional laser processing of metals will form serious heat affected zone, micro cracks, burrs and recast layer, resulting in rough machined surface and serious slag accumulation. As a new type of laser-waterjet composite processing method, waterjet guided laser can reduce or even eliminate heat affected zone, thermal crack, recast layer and burr. It has the advantages of high surface quality, strong depth ability and large depth-to-diameter ratio structure. Nickel-based single crystal superalloy is widely used in advanced aero-engine turbine blades for their excellent overall performance. With waterjet guided laser processing technology, this paper study the influence of process parameters on the grooving morphology and quality of DD6 nickel-based single crystal superalloy. A multi-factor study on the influence of laser power, laser repetition frequency, waterjet velocity and feeding speed on grooving was carried out with a self-developed waterjet guided laser processing device. The depth-to-width ratio and sidewall taper of the machined groove were measured and analyzed by using a three-dimensional confocal laser scanning microscope. The experimental results show that the grooves taper can be decreased with reducing the laser repetition frequency and increasing the laser power. The grooves large depth processing is improved by reducing the feeding speed, increasing the laser power, reducing the laser repetition frequency and increasing the waterjet velocity. The cutting experiment of 1 mm DD6 nickel-based single crystal superalloy was achieved with better processing process parameters, and it was found that the upper and lower surface roughness of the cutting surface was inconsistent, providing a theoretical basis for the study of high quality processing of nickel-based single-crystal superalloy by waterjet guided laser.

Laser shock peening without protective coating leads to mechanical and thermal loads of materials, resulting in surface melting and re-solidification. In this paper, the effect of laser shock peening (LSP) with and without protective coating on the surface behavior of AZ31B magnesium alloy was studied. Study on surface mechanical property of magnesium alloy by different LSP process parameters. The effects of different LSP parameters on the surface properties of the sample were studied by microhardness test, phase analysis, et al. The results show that the increase of laser power density, the surface hardness of the sample increases. Compared with the LSP with protective coating, the LSP without protective coating increases the surface roughness. And resulting microstructure and residual stress state were studied, After LSP treatment, diffraction peaks shift to high angle direction, resulting in residual compressive stress on the surface of the material.

The noise floor performance of optical frequency transfer system is mainly affected by the change of optical length of the Interferometry and refractive index induced by ambient temperature variations and mechanical vibration effects. At present, the universal installation is connected by fiber components for optical frequency transmission over fiber link. However, for signal detection at the local site, due to the welding technology of fiber, the length between the fiber units is limited to a certain length, which makes it difficult to achieve high-symmetry detection at the local site, and the asymmetric part are susceptible to environmental disturbance. Therefore, in order to minimize the influence of noise base on transmission system, this paper investigates a compact and integrated optical path module based on free space. The spatial optical module integrates beam prism, half wave plate, quarter wave plate, fiber collimator, 0 degree mirror and Faraday mirror in the size of 5 cm×6 cm, which can reduce the connection distance of local devices from 10 cm to 3 cm. At the same time, the local reference light transmission in air medium is more stable than in the fiber medium, which can reduce the noise level of the reference end and improve the stability of the system. In the experiment, the local end based on the spatial optical path and that based on the fiber path is compared and tested in a non-temperature-controlled environment. The experimental results show that the spatial optical path has obvious advantages in both short-term stability and long-term stability. It can decrease the noise floor level of the optical interferometry used for phase noise cancellation in a optical frequency transmission system via fiber, and provide a potential optimization space for long-distance transmission.

With the development of high power fiber oscillators, it is urgent to fabricate fiber Bragg gratings (FBGs) on large core fibers. Here, a pair of FBGs in fibers with core diameter of 30 μm are fabricated based on femtosecond laser phase mask scanning method. The reflectivity of high-reflectivity FBG (HR-FBG) is more than 99% with the central wavelength of 1080 nm and the 3dB bandwidth of 3.6 nm. The reflectivity of output coupler FBG (OC-FBG) is about 10% with the central wavelength of 1079.8 nm and the 3dB bandwidth of 2 nm. Furthermore, an all-fiber oscillator is built based on the fs-written FBGs, and the maximum output power of 6.4 kW is realized with the optical-optical conversion efficiency of 74%. The temperatures of HR-FBG and LR-FBG are 90 and 49℃, respectively. This work demonstrates that the large core diameter FBG written by femtosecond laser has excellent performance, which is of great significance for the development of high power fiber oscillators.

This paper proposes a multi-stage cooling system based on TEC (Thermo Electric Cooler), vapor chamber, heat sink and fan for the high power compact laser diode in the high temperature and mobility environment. Using Flow Simulation and ANSYS software, the temperature field and thermal stress of the multi-stage cooling system under steady state are discussed respectively, and the multi-stage cooling system model is optimized according to the two simulation results and the physical test is carried out. The results show that the designed cooling system can achieve a continuous and stable output of more than 70W from the laser at both room temperature of 20°C and high temperature of 55°C.

Aiming at the issues of low machining efficiency and difficulty in keeping consistency of machining accuracy of micro array holes with high surface quality. This paper proposed a laser and in-situ electrolytic machining technology for processing array holes, which utilized the advantages of high laser machining efficiency and good surface quality electrochemical machining (ECM). Firstly, laser was used to perform high-efficiency drilling of prefabricated micro array holes on workpieces that was covered with insulating layer, and then the recast layer and taper of prefabricated holes were removed by ECM. To verify the feasibility of the proposed method, laser prefabricated of the array holes with the diameter of 0.8 mm and the in-situ electrolytic recast layer removal were carried out on the Inconel 718 workpiece. Influences of laser scanning speed, defocusing distance, scanning times and insulating plate thickness on the taper of prefabricated hole were investigated experimentally. The optimized laser processing parameters were as follows: scanning speed 60 mm/s, defocusing distance 1.5 mm, scanning times 50, and insulating plate thickness 0.4mm. Results of in-situ ECM showed that the recast layer on the surface of the laser processed holes could be removed, indicating that the laser and in-situ ECM could achieve high efficiency and high precision machining of micro array holes without recast layer.

Backward light by stimulated Brillouin scattering (SBS) induces the final transport mirror laser damage, which has been considered a bottleneck problem in developing high-power and high-energy laser facilities. In this work, an improved continuous phase plate (CPP) model and a backward SBS model were established based on the G-S algorithm and the Fresnel diffraction transmission algorithm to simulate the backward SBS to the final transport mirror. This study discussed the propagation characteristics of backward SBS. The research results showed that the distribution of the backward SBS transmitted to the final transport mirror was determined by the phase structure of the continuous phase plate attached to the back-transmission process. By optimizing the CPP design, reducing the transmission distance, reducing the intensity modulation, and controlling the phase of the incident beam, the modulation of backward SBS can be suppressed, which has great significance in improving the laser-induced damage threshold to the final transport mirror.

Coupled resonant optical waveguide (CROW) gyroscope is an important type of integrated optical gyroscope based on Sagnac effect. However, the traditional CROW design method relying on empirical adjustment of parameters is deficient in achieving its best capability and the poor Sagnac effect of micro-scale devices leads to unsatisfactory performance of integrated devices. Therefore, the present study proposes a new approach to design CROW gyroscope by applying intelligent optimization algorithm (PSO: particle swarm algorithm) to design CROW gyroscope. Three aspects of work will be explored: Firstly, a new evaluation index is proposed to evaluate the efficiency of integrated optical gyroscope area utilization (EGA). Secondly, The performance limits for different losses and the accuracy limits and related parameters that can be achieved by increasing the resonator area at different losses are also explored. Finally, we designed theoretical performance (The angle random walk) up to 29.1𝑑𝑒𝑔/√ℎ and only 1mm × 1mm in size.

An 885nm LD end-pumped burst-mode laser with high repetition frequency and low thermal effect is introduced in this paper. The laser can solve the problem of high repetition frequency and high energy in the traditional continuous pulse output mode, and can meet the requirements of light source of airborne lidar well. The laser adopts the main oscillating power amplification (MOPA) structure. The oscillating stage uses 885nmLD pulse pumped Nd:YAG crystal, which can reduce the thermal power consumption of the laser. The electro-optic Q-switch is used for intra-cavity modulation, and the output pulse train with a repetition frequency of 4Hz, each pulse train contains 60 sub-pulses with a repetition frequency of 1kHz.Finally, the fundamental frequency light with central wavelength of 1064nm, sub-pulse repetition frequency of 1kHz, single pulse energy of 6.1mJ and beam quality is obtained. In the amplification stage, 885nm end-pumped Nd: YAG crystal was used. After one-way amplification, the laser output with sub-pulse energy of 15.7mJ, pulse width of 12ns and beam quality was obtained.

Laser cleaning of manmade contaminants from stone samples have been performed experimentally using picosecond (ps) and nanosecond (ns) laser pulses. Regarding the surface roughness after laser cleaning, optimal cleaning parameters using ps laser have been obtained. Discoloration effect induced by ns laser cleaning of stone sample is improved with the usage of ps laser. The comparison on the roughness and elemental analysis of the cleaned area in the experiment also demonstrates the advantages and effectiveness of ps laser cleaning of stone samples.

In this paper, an integrated semiconductor disc laser is designed with the integrated design of the laser source, optical system and heat sink system. The 808 nm VCSEL array is used as the pump source and the Nd:YVO₄ crystal is used as the gain medium. The pump source and the gain medium are placed on the same substrate, and both of them share a common cooling system. The collimating optical system of the VCSEL array and the reflective focusing optical system are designed using ZEMAX software, and the focusing spot radius is 1.3 mm, which matches with the theoretical calculation of the crystal pump spot size. The feasibility of integrating the pump source and gain medium in a same cooling system is analyzed using Flow Simulation and ANSYS software, and an air-cooled thermal system is designed by comparing the thermal simulation results of the water-cooling method for verification. Realization of opticalmechanical thermal integration design.

A frequency converter is usually used in high-power laser facilities to triple the frequency of the incident laser. It consists of a KDP crystal and a KD*P crystal in series. The measurement of the detuning angles of the frequency converter is essential for improving the frequency conversion efficiency. In this paper, we propose a measurement method that uses a diverging beam to illuminate the frequency converter and get the detuning angles by analyzing the light intensity distribution of the third harmonic laser. The simulated results show that there is a strict linear relationship between the characteristic parameters and the detuning angles of frequency converter, verifying the feasibility of this method. Compared with existing measurement methods, its optical path is simple, and the single measurement time can be shortened to a few minutes from a few hours.

Water jet-guided laser technology is an efficient processing technology that offers the advantages of a small heat-affected zone and strong depth capability when processing a variety of difficult-to-process materials. However, the surface of the laminar water column can form irregular disturbances due to nozzle damage and other factors, ultimately leading to an uneven distribution of laser light intensity, causing a loss of laser power. In this paper, the relationship between the quality, morphology and coupling alignment errors of the water column on the optical transmission efficiency of water-guided lasers is investigated in depth with ray tracing method. Besides, the water column surface variable-angle prismatic disturbance model is established, considering the characteristics of the real water column to research the impact of the real situation relationship. The results show that the loss of laser energy is more severe as the complexity of the surface morphology of the water column increases. In addition, laser coupling alignment errors are studied. The results show that a circular distribution is formed in the water column when the alignment deviation occurs. Finally, the reasons affecting the laminar flow conditions are analyzed to provide theoretical support for efficient laminar coupled light transmission.

Due to the advantages of ultra-broad bandwidth absorption and easy fabrication, passively mode-locked ultrashort lasers using two-dimensional (2D) materials as saturable absorbers (SA) have attracted extensive attention in recent years. In this experiment, the structure and light absorption properties of 2D nickel-cobalt layered double metal hydroxide (NiCo-LDH) nanosheets are characterized. The nonlinear absorption coefficient of NiCo-LDH are measured by Z-scan method to be -1.1 cm/GW. Using the NiCo-LDH SA, passively mode-locking is realized in a Nd:YVO₄ bulk laser near 1 μm, a Nd:Y_0.15V_0.85O₄ bulk laser near 1.3 μm and a Tm:YAG ceramic bulk laser near 2 μm. In the 1 μm passively mode-locking experiment, a continuous wave mode-locking (CWML) laser is obtained at 1065.92 nm with a repetition rate of 69 MHz and a pulse width of 18.0 ps. To our knowledge, this is the first time a CWML laser has been obtained using a layered double hydroxides (LDHs) SA. In addition, Q-switched mode-locking (QML) lasers are obtained based on NiCo-LDH SA at 1.3 μm and 2 μm. The experiments demonstrate that NiCo-LDH mode locking is a very promising practical technique for directly generating ultrashort pulsed laser from a laser oscillator.

Spectral beam combining technology based on diffraction grating is an effective method to obtain tens of thousands of watts or even hundreds of thousands of watts of high-power and high beam quality laser. The high power linearly polarized narrow linewidth fiber laser is an ideal sub-beam source in spectral beam combining systems. Limited by stimulated brillouin scattering and mode instability, the power increase of narrow linewidth lasers has been limited, especially in linear polarization systems. In this paper, we report a high-power line polarized narrow line width fiber laser. The white noise signal (WNS) phase modulation and the pseudo-random binary sequence (PRBS) phase modulation were combined to widen the single-frequency laser line width, and then the three-stages fiber amplifier was used to amplify the narrow-line width laser for power. A high power line polarized narrow line width laser with a center wavelength of 1064nm, a power of 2070W and a 3dB line width of 23GHz was finally obtained. The laser polarization extinction ratio is greater than 14dB.

(Tb_0.7Lu_0.3)₂O₃ transparent ceramics were prepared by hydrogen pre-sintering and hot isostatic pressing treatment. ZrO₂ was added as sintering aid to restrain the abnormal grain growth. The microstructure evolution and linear shrinkage changes of the (Tb_0.7Lu_0.3)₂O₃ transparent ceramics in the range of 1400℃~1700℃ were investigated. It can be seen from the results that the linear shrinkage of ceramics increased nonlinearly with the increase of the sintering temperature. In the range of 1550℃~1600℃, the (Tb_0.7Lu_0.3)₂O₃ ceramics had a higher shrinkage rate. And the shrinkage rate slowed down when the temperature exceeded 1600℃. The samples prepared by 1550℃ hydrogen pre-sintering combined with 1550℃ hot isostatic pressing sintering showed good optical property. The average grain size was about 1.69μm and the highest transmittance reached 74.81% @1064 nm.

In this study, transparent Nd: YAG ceramic was fabricated by gel casting of iso bam system using a dispersant composed of tetramethylammonium hydroxide (TMAH) to modify the rheological properties of slurry. The effects of dispersant content on the dispersibility and viscosity of slurry were studied, as well as the microstructure and light transmittance of the obtained transparent ceramics were also analyzed through the introduction of 0 − 1.5 wt.% TMAH. The results showed that the dispersion mechanism of TMAH is mainly to control the electrostatic property and the alkaline Zeta potential value of the slurry. The electrostatic repulsion of ceramic particles in the slurry could be effectively increased through the dispersing action of the additive, thereby reducing the viscosity of the slurry and improving the fluidity of the slurries. Under the TMAH content of 1 wt.%, a high-fluidity and good dispersion of Nd: YAG slurry with a solid load of 78.8 wt.% was obtained. A low viscosity of 72.89 mPa·s was achieved under shearing of 100 s^-1, and a dense uniform body was obtained by self-gelling reaction. Highly transparent Nd: YAG ceramics were obtained after vacuum reaction sintering at 1780°C for 10 h, with a transmittance of 75.12% at 1064 nm. In all, the TMAH dispersant could effectively improve the molding properties of PIBM single system gel injection molding transparent ceramics.

Graphene films are characterized by high electrical conductivity and high optical transmittance. In this paper, we mixed graphene solution and polyvinyl alcohol (PVA) solution to make different concentrations of graphene solution. The electrical conductivity, optical transmittance, and phase shift of multilayer graphene films were measured in the THz range by coating graphene solution on the substrate. According to experimental results, the following conclusions are drawn: the film with a larger proportion of graphene has a smaller square resistance, that is, a better conductivity, a smaller transmittance, and a phase shift in the terahertz range under the same thickness. Subsequently, the solution made of 1:1.75 PVA and graphene solution was coated on the outside of the glass sheets containing E7 and HTD liquid crystals, respectively. The distance between the two glass sheets was 800um, which was the thickness of the liquid crystals. Then, a magnetic field is added along one side of the glass sheet (defined as the X direction). Through experiments, it is found that when the voltage is added to 100V (130V), the orientation of E7 (or HTD) liquid crystal can completely change the direction of the electric field. And in the case of the only magnetic field, E7 (or HTD) liquid crystal produces 0.5π phase difference corresponding frequency is 0.8THz (0.6THz), π phase difference corresponding frequency is 1.4THz (1.0THz).

Recently, researchers have found that the friction pairs with diverse surface micro-textures have excellent wear resistance. However, the traditional micro-texture processing technology is difficult to accurately control the depth and shape of the texture. In this paper, in order to obtain the micro-texture with accurate depth and regular shape, the femtosecond laser was used to process micro-texture on the surface of 7075 aluminum alloy, and the laser process parameters were optimized to realize the precision and smoothness of micro-texture depth and shape. The results show that the increase of laser processing power and scanning times can effectively lead to the increase of microtexture depth within a certain range, and the decrease of filling space has the similar effect. However, the depth of micro-texture decreases with increasing scanning speed, and excessive scanning speed can result in the uneven structure of micro-texture, especially on the edge and at the bottom. Subsequently, the quality of micro-texture is decreased. Therefore, it is necessary to control the processing parameters to achieve high quality process, so as to obtain a smooth edge of the micro texture.

Since the beginning of the new century, energy and environmental issues have always been a hot topic of discussion and research. With the rapid consumption of traditional fossil energy and environmental problems becoming increasingly prominent, it is urgent to find efficient energy storage devices. Lithium-ion battery is a common and representative energy storage device in secondary batteries, and the structure of its electrode material is a key factor affecting the electrochemical performance and safe service life of the entire lithium-ion battery. Laser is widely used in electrode processing due to its high energy concentration, small heat-affected zone, high processing precision, and low requirements for processing environment. Laser processing technology for cutting, drying, constructing three-dimensional micro/nano-structured electrodes or directly printing battery materials can greatly reduce manufacturing costs and improve the electrochemical performance. In this study, the application of several laser processing technologies in the structure of the negative electrode of lithium ion battery is reviewed. The application of laser in electrode cutting, drying and annealing is discussed from the perspective of laser energy concentration and small thermal influence. Starting from the relationship of efficiency, the strategy of constructing a three-dimensional structure on the negative electrode of lithium ion battery by laser processing technology is summarized. The electrochemical performance and the service life of lithium ion battery are prospected.

The study of pulse dynamics in fiber lasers is of great significance for the generation of high quality ultrashort pulses. Reasonable control of the intra-cavity dispersion can improve the pulse width, energy and noise characteristics. We report an all-polarization-maintaining (PM) dispersion managed thulium-doped fiber laser (TDFL) based on nonlinear amplified loop mirror. Conventional soliton, stretched-pulse soliton and dissipative soliton generation are demonstrated, when the oscillator operates with different net dispersion. Self-starting and stable mode-locked operation is achieved with different types of soliton pulses.

Due to the strong light–matter interactions, van der Waals semiconducting materials have shown their great potential in the development of high-performance photodetectors. However, the van der Waals semiconducting devices via conventional growth method often introduce defects or are in the form of isolated flakes, which hinders the optoelectronics from widespread applications. In this paper, van der Waals semiconductor indium selenide (InSe) fibers for photodetection were developed based on thermal drawing. Meters level length of InSe fibers have been fabricated through thermal drawing, and the problem of easy cracking of InSe is solved. The InSe fibers have high crystallinity, and it is found that the cleavage planes have a preferential orientation. The InSe fibers show a high-speed response to modulated 639 nm laser irradiation with up to 10 kHz repetition rate. In addition, the photoelectric response of the fibers were further improved through annealing by CO₂ laser.

In this paper, in order to identify and trace the single silicon wafer, the robustness of wafer identification using micro ID on polished silicon wafers is investigated. A dot-matrix encoding scheme for forming reliable, machine-readable identifying codes on the wafer is used. The quality of dot concerning marking depth, the dot size, robustness of code detection by automatic vision inspection is investigated. The topography and the depth, the dot size are evaluated with VHX6000 microscope and Bruker Contour GT 3D Surface Profiler. Codes either alphanumeric characters or data matrix codes with different the topography and the depth are detected by the In-Sight 1741 image Code Reader. Dot diameter ranges from 15.4 to 70um and dot depth ranging from 0.287um to 3.797 um are achieved. The minimum readable Data Matrix codes is 2.33*0.53mm,the average read rates of 100% are already achieved with the Data Matrix codes With 3.88*0.65mm.

Polarization smoothing is a means to increase the uniformity of the focal spot by using polarization characteristics of light. It can theoretically reduce the contrast of focal spot to 0.707 times, and because of its real-time modulation characteristics, it can significantly suppress backscattering and improve the beam-target coupling performance of high-power laser facilities. However, in the traditional polarization smoothing scheme, the crystal used for polarization smoothing (largeaperture KDP crystal) will produce transverse stimulated Raman scattering in the high-power ultraviolet band, which will cause crystal damage. To prepare for the exploration of new single beamlet polarization smoothing schemes, we conduct a simulation study on the scheme of modulating the full Poincaré beam with a single transmission element. The results show that a single waveplate with a fast axis that rotates with polar angle and a phase retardation that increases with radius can modulate a full Poincaré beam, and we analyze the properties of this full Poincaré beam. Then combined with the engineering parameters, we analyzed the polarization smoothing performance of the full Poincaré beam with square aperture laser input. The performance was quantified by several target focal spot intensity evaluation indexes, and the results show that the use of the full Poincaré beam for polarization smoothing can reduce the contrast of the focal spot effectively, and the reduction range is close to the theoretical maximum value. And there are advantages in suppressing high energy density hot spots and optimizing the spatial frequency of the focal spot.

Silicon wafers are the raw material for chip manufacturing, and the identification code is formed on the surface by laser engraving, which is an important part of the traceability chip management cycle. In this paper, the 532nm Nd: YVO₄ laser is used to build a laser marking system, and the stability and energy distribution of the laser light source are analyzed. The laser marking system is used to mark the surface of the silicon wafer with dot matrix, and the white light interferometer is used to analyze and measure the ablation pit at a single point, and the process effect of the system on the wafer marking is evaluated from the depth of the single point. In this paper, the process research of silicon wafer marking is carried out by changing the laser power, PRF (pulse repetition frequency), the number of laser pulse and defocus amount of the system. The research results show that: 1) 532nm Nd: YVO₄ laser has the highest energy stability at the maximum current and 20 kHz. 2) Under the condition that other system parameters such as power and repetition frequency remain unchanged, the depth of marking can be improved by increasing the number of pulses. 3) Under the condition that other parameters of the system such as the number of pulses and power remain unchanged, the balance between marking quality and marking efficiency can be achieved by optimizing the laser repetition frequency. 4) Under the condition that other parameters of the system such as power, PRF, and the number of pulses remain unchanged, there is a certain range of power. The change of defocus amount is the most sensitive, and with the increase of defocus amount, the dot depth and aperture first increase and then decrease.

Strong terahertz chiral manipulation plays a vital role in polarization imaging, chiral spectroscopy, and multichannel communications. Here, a composite structure based on the double-layer metasurface sandwiched with the ultrathin liquid crystal layer is proposed to realize a strong terahertz chiral manipulation. On account of breaking mirror symmetry in the propagation direction and the local field enhancement effect in the cavity, the composite structure possesses a strong terahertz chiral response. Moreover, this terahertz chiral response can achieve a large tuning range by changing the optical axis of the liquid crystal: the experimental co-polarization circular dichroism can achieve a large controllable range of −31dB to 30dB at 0.772 THz and a chirality control range from 11dB to −22dB at 0.759 THz. This composite device demonstrates rich characteristics for the feasible manipulation of THz chiral response, which has greatly promoted the development and practical application of THz polarization and chiral control devices.

Reticle-based seekers have significantly advanced for 60 years and widely used in modern warfare as a major threat to the safety of all types of airborne platforms including fighters, helicopters, transport aircraft and even civil aviation. Reticle-based seeker can convert the light signal radiated by the tracking target into a modulated signal carrying target orientation information, and the tracking effect is affected by noise, complex background and various jamming signals. In this paper, we analyze the target location extraction mechanism of typical reticle-based seekers and the dynamic simulation of the process of jamming with reticle-based seeker by mid-infrared laser with different modulation methods is developed using Matlab. The main factors affecting the effectiveness of IR countermeasures is obtained. The results show that the intensity, frequency and phase of the jammer signal have a certain influence on the tracking accuracy of the reticle-based seeker, with the laser power having the greatest influence on the jamming effect of reticle-based seeker. This study provides a theoretical basis for the optimization of operational indicators for infrared laser countermeasures.

Deformed square microcavities composed of two partly overlapped square microcavities are proposed and investigated theoretically and experimentally. Single-mode lasing with the maximum side-mode suppression ratio (SMSR) of 39 dB and 52 dB are obtained for the deformed square microcavity lasers, connected an output waveguide to the jointed region and a vertex of the square microcavities, with a side length of 10 μm, respectively. Furthermore, higher output power is obtained for the deformed square microcavity laser with a vertex output waveguide than that with an output waveguide to the jointed region.

In high power laser facilities, phase modulation is required to broaden the laser spectrum, suppressing the SBS buildup in large optics. Spectral fail-safe module is responsible to monitor the spectral bandwidth of every pulse and inhibits the pulse to propagate if phase modulation fails. We demonstrate a multi-color fail-safe module, intentionally induces FM-to-AM conversion on the monitored laser with a fiber filter to convert GHz phase modulation into GHz amplitude modulation that can be measured with an AM detector. By choosing proper fiber filter parameters, the module is applicable to high-power lasers with multiple center wavelengths. In experiment, we achieved fail-safe condition within 1nm detection bandwidth, which can be even larger if a wider bandwidth fiber filter is used. In addition, this module has the advantage to work without temperature control, making it more practical for high-power laser facilities.

In this paper, a phase-change-cooled active mirror amplifier with high thermal conductivity composites is presented to meet the thermal management requirement and the payload limit of laser amplifiers in the space environment. And a three-dimensional transient model of solid-liquid phase cooling is developed to predict the phase change process and the thermal effects in the active mirror amplifier, in terms of temperature, thermal stress, thermal deformation and thermal-induced wavefront distortion. The measured transient temperature distributions agree well with the results of the transient model, which verify the accuracy of the model. We expect that this investigation will assist in the design and optimization of the high energy, high average power lasers.

This paper discusses the frontier applications of ultrafast laser processing technology in the printed circuit board industry. High-density interconnect boards have characteristics of massive micro buried and blind holes. Currently, the industry commonly operates CO₂ laser to produce microvias of about 100um diameter with very high processing efficiency. However, due to the pulse duration of the CO₂ laser being in the microsecond order, the thermal effect of processing is significant, see Figure 1. It is difficult to achieve high-quality micro vias of 75um and below. This paper systematically studies the processing capability of lasers with pulse duration of picosecond, nanosecond, and microsecond for 50μm diameter micro blind vias on copper-clad laminate. The quality of blind vias is evaluated through characterization such as scanning electron microscopy, laser confocal microscopy, and optical microscopic. The interaction mechanism between the laser and various materials is discussed in detail. This paper discusses the interaction mechanism between laser and materials such as copper foil, glass fiber, and resin in copper-clad laminates. Heat-affected zone decreases with decreasing pulse duration. The picosecond laser can effectively remove copper foil, glass fiber, and resin with the highest precision among the three lasers. Meanwhile, picosecond laser drilling equipment can simplify the processes necessary for drilling with CO₂ laser equipment. That helps offset the disadvantage of the low power of ultrafast lasers to a certain extent. The mass application of ultrafast lasers in the PCB industry will come soon.

Wavefront distortion is an important limiting factor for improving the output performance of high-power laser devices. It is an effective way to control the wavefront distortion via adaptive optics (AO) wavefront control technology. In the present paper, the research of wavefront control technology based on laser device is carried out, along with the feasibility and effectiveness of wavefront control technology are also verified. The functionality and reliability of major hardware components, such as the high-voltage power supply modules, the communication modules and the piezoelectric drivers, have all passed the offline test. The online test results show that the wavefront distortions for each of eight beam lines in the laser device has been corrected by the deformable mirrors installed in the main amplifier and the final optical assembly (FOA). Focal spot measurement shows a significant improvement in the focusing performance, with 95% of the frequency-tripled laser energy encircled in 30 times diffraction limit (DL). It is proved that the wavefront control technology can degread wavefront distortion generated from laser translating, and ensure a smooth beam transmission and a high output beam quality for the high-power laser devices.