This PDF file contains the front matter associated with SPIE Proceedings Volume 11333, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

A Ho³⁺-doped photonic crystal fiber laser with output wavelength of 2077nm has been demonstrated using a 1992nm Tm³⁺-doped fiber laser with output wavelength of 1992nm as a pump source. And the optical- optical conversion slope efficiency is 41.3%. In order to optimize the output power of the Ho³⁺-doped photonic crystal fiber laser, a simple quasi-three level system theoretical modeling is developed in the condition of Stark-splitted energy level diagram of holmium ion. We obtain the theoretical optical- optical conversion slope efficiency 43.5%, which is higher than the experimental 41.3%. Furthermore, the relative deviation of the η is 5%, which shows the theoretical data is good agreement with experimental data. According to the modeling, the influence factors of the output power have been theoretically studied, in detail. The results show that there are an optimal range of Ho³⁺-doped concentration n₀, transmittance of coupled output mirror T₂ and length of the PCF L, respectively. Furthermore, the output power is approximately equal to maximum in the range of the optimal value.

In this paper, we demonstrate a spectral beam combining scheme of two ytterbium-doped fiber lasers, running at different wavelengths. An edge filter with high damage threshold (>20 MW/cm² ) and steep rising edge (<2 nm) is employed as the combining element to overlap the two output beams in the near and far fields. 6.2 kW combined output power is achieved with an efficiency of 97%, which proves the high efficiency of the filter for both the reflection and transmission cases. Despite the broad emission spectrum of the single channel, the beam quality of the output is approximate with the incident emitters in horizontal and vertical directions. In terms of the measurement result conducted with thermal imaging camera, the growth of temperature on the edge filter during the combining process is well within the acceptable range. Compared with the grating based spectral beam combining (SBC) schemes, it permits the efficient combining of broader spectrum and arbitrarily large beams, which shows the potential of the filter-based spectral beam combination system. Scaling by additional and more powerful channels, higher combined output power appears to be feasible.

A laser radar used in an automatic driving system was designed to operate normally in rainy and foggy weather while ensuring eye safety. The laser radar uses the principle of triangulation to measure the distance while adjusting the position of the focused light source by the beam expanding and focusing module. The laser radar used a home-made passively Q-switched Er:YAG laser that used a home-made TiS₂ as a saturable absorber with an operating wavelength of 1645 nm. At an absorption pump power of 10.54 W, the passively Q-switched Er:YAG laser had a pulse repetition frequency of 37 kHz, a maximum average output power of 1.44 W, a pulse duration of 1.1 μs, and a pulse energy of 36.39 μJ.

We demonstrate a 2.1 μm Tm/Ho composite laser via diffusion-bonding the Tm-doped and Ho-doped YAG crystals into a single bulk structure, which facilitates the direct use of common AlGaAs diode lasers (LD) for an efficient and compact Ho laser source at room temperature. Locking the pump wavelength at absorption peak of 784.9 nm of the Tm-doped region of the composite gain medium, maximum output power of 6 W at 2122 nm was obtained with a slope efficiency (SE) of 40.1% and conversion efficiency (CE) of 33.6% from absorbed LD power to Ho laser, which is comparable in efficiency with the 1.9 μm LD resonantly pumped Ho lasers. Above 1.6 W Ho laser power at operation temperature range from 9 °C to 27 °C could also be realized by side-pumping absorption band of the Tm-doped region at 808 nm, which indicates a 40 nm broad pump wavelength range for the Ho laser at room temperatures. Via broad-band coating the output coupler with the same transmittance from 2000 nm to 2100 nm, synchronous Tm laser and Ho laser oscillation at both 2.1 μm and 2 μm was observed, where signal of the Tm laser was faded finally with the increased pump power. Furthermore, thermal lens and temperature distribution of the composite gain medium is analyzed basing on a proposed thermal model recently.

In the past decade, two-dimensional (2D) materials have attracted increasing attention due to their energy band structure, optical properties and excellent performance in ultrafast photonics and nonlinear optics. As a kind of new 2D ternary layered material, NiPS₃ can exhibit more novel electrical, optical and magnetic properties compared with those unary and binary 2D layered materials because of higher chemical diversity and structural complexity. In this work, we demonstrated a passively Q-switched operation based on few-layer NiPS₃ as a saturable absorber (SA) in an erbium-doped fiber (EDF) laser. And the Q-switched output was achieved when the pump power at 40~105 mW. To our best of knowledge, it is the first time to utilize the NiPS₃ as a SA in pulse laser generation.

The paper adopts the passive mechanical athermalization method to ensure the laser radar optical launching system works steadily and continuously in the temperature range of -10℃ to 50℃. Firstly, the weight ratio of the impact of temperature variations on the optical launching beam-expansion lens group is analyzed to carry out the athermalization design for the front multi-lens group. Next, the ZTC4 that matches the linear expansion coefficient of lens materials is selected based on analyzing and comparing the attributes of the lens barrel. Afterward, the redesigned elastic space ring is adopted to keep the spatial distance between each lens. Meanwhile, the distance is optimized and analyzed to construct the equation set for the size and axial direction of the elastic space ring and the stress variation. The equation set is later applied to making the rational design for the elastic space ring that achieves spatial localization. Meanwhile, optimal design parameters are selected for the elastic space ring to reduce contact stress and ensure axial consistency of the optomechanical system. Lastly, the flexible structural clamping ring is used for fastening. According to analytical results, the maximum axial displacement of the system is less than 0.06mm when the temperature of system changes; the surface accuracy of each lens is less than λ/8; the maximum stress of each lens is smaller than the yield strength of BK7 and SF8 glass lens material. All parameters meet the requirements on the athermalization design.

Laser welding technology is widely applied in railway vehicles manufacturing, improving the appearance quality, improving the strength and reducing the weight. The outer surface of the stainless steel railway vehicle is not coated and it has high requirements on appearance quality, when the laser welding process is applied, the length of the ramping at the arc-starting position and the arc-closing position is required to ensure that there is no obvious deformation left on the outer surface. The laser welding process with different ramping length is investigated to clarify the influence of the ramping length on the deformation of the weld outer surface, to optimize the ramping length in the process. The comparison tests of different ramping lengths were carried out. The surface deformation, residual stress and tensile strength of different ramping length joints were compared, and the influence of the length of ramping on the deformation of the welding seam is analysed comprehensively. And with the increase of the length of ramping, the deformation of the welding seam decreases. There is no obvious influence on the weld arc position when we choose the ramping length from 3 - 5 mm, with the maximum deformation at the weld arc position about 100 μm.

Changes in the polarization properties of a spatially and spectrally partially coherent stochastic electromagnetic Gaussian Schell-model (EGSM) ultrashort pulse laser beam propagating through the atmospheric turbulence are investigated. We derive analytic equations for the spectral degree of polarization and the polarization angle in terms of the extended Huygens-Fresnel principle and elements of the 2×2 cross-spectral density function matrix of the electric field. Within the framework of the Tatarskii model of the turbulent atmosphere, which taking the inner scale of the turbulent eddies into consideration, the dependence of along the z-axis and off the z-axis the spectral degree of polarization and the polarization angle of a stochastic EGSM ultrashort pulse laser beam on the parameters of the source including spatial coherence length and temporal coherence length are stressed and illustrated numerically. Results show that the spectral degree of polarization and the polarization angle of the EGSM ultrashort pulse laser beam propagating through the atmospheric turbulence are determined by the parameters of the source. Our results have potential applications in atmospheric remote sensing and ground-to-satellite optical communications.

A Tm:YAP slab laser with double-end-pumped and high efficiency under room temperature is introduced. Considering the cooling of the end faces and lateral faces of the crystal, analyses of the thermal effects in which all six faces cooled by the convection cooling mechanism was assumed to solve the equations of heat conduction. By using the double-concave geometry to offset thermal lens effect, the maximum output power was 25.02W at the incident pump power of 75.97W, corresponding to the optical-to-optical efficiency of 37.05% and slope efficiency of 35.85%. F-P etalon is inserted in the cavity to control laser FWHM line width of 0.44nm at 1938.7nm. And the optical beam quality is measured when pumped power is 20W,which is the beam quality factor of M2 was estimated of 3.25 in x-direction and 2.79 in y-direction.

In order to further improve the infrared / radar compatible stealth performance of La_0.7Ba_0.3MnO₃ powder. The perovskite type La_0.7Ba_0.3MnO₃ powder were prepared by sol-gel, and its surface was metallized by electroless plating. The phase structure, surface morphology and composition of samples before and after electroless plating were characterized by means of XRD, SEM. IR-2 infrared emissivity tester and vector network analyzer were used to analyze the infrared emission and radar absorbing performance before and after electroless plating. The results show that, the infrared emissivity of the samples in the infrared range of 8~14 μm and 3~5μwas significantly reduced by electroless plating. The infrared emissivity in 8~14 μm decreased from 0.818 to 0.604 after plating, in the 3~5 μm decreased from 0.768 to 0.513, and the reduction rate was about 0.2. The peak of the radar wave absorption of the electroless Ni-P alloy layer is lower than that before plating. The frequency of the maximum absorption peak is shifted from low frequency to 8.2 GHz before plating, The effective absorption bandwidth is from 3 GHz before plating to 4.5 GHz after plating. The surface modification of La_0.7Ba_0.3MnO₃ powder by electroless plating can double the infrared and radar wave stealth performance and provide a new idea for the research of infrared / radar compatible stealth material.

A simple and effective tunable and switchable L-band multi-wavelength polarization-maintaining erbium-doped fiber laser is proposed and demonstrated. A Mach-Zehnder interferometer with a fiber Bragg grating inside one arm used as the wavelength selective filter makes the output wavelength at the L band. The nonlinear polarization rotation effect induced by a 5-km long single mode fiber, a polarization controller (PC) and polarization-dependent isolator is used to effectively suppress the mode competition. Thus the stable all-fiber ring cavity structure with multi-function operation is realized. The laser outputs of the single-wavelength can be tuned about 12 nm with an interval of 1 nm in L band. The side-mode suppression ratios (SMSRs) of these lasing lines are all over 60 dB. And single-wavelength, dual-wavelength, triple-wavelength and quadruple-wavelength can be switched by appropriately adjusting the PC. The SMSRs of multiwavelength lasing lines are all over 50 dB. The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.

Aiming at the characteristics of signal fading caused by the intensity fluctuation and the off-axis drift of the underwater wireless optical communication, a method of laser-based trans-media transmission from atmosphere to underwater employing low density parity check (LDPC) and pulse position modulation (PPM) joint coding is proposed. The encoded frame structure is studied. Furthermore, by simulation, the performance of LDPC and PPM joint coding in Gaussian channel and weak turbulence channel is analyzed and compared with that of the uncoded PPM system. A practical communication system based on Field Programmable Gate Array (FPGA) is established and relevant lab tests are carried out. The simulation results show that the joint coding of LDPC and PPM can significantly improve the system error performance under these two channels, and the performance of Gaussian channel is better than that of weak turbulence channel. It is verified by the tank experiment that the system combining LDPC and PPM can obtain 1.5 dB code gain compared to the uncoded PPM system at the same bit error rate, which fully demonstrates the anti-interference ability of the system combining LDPC with PPM in data transmission.

First-principles calculations based on the density function theory (DFT) are implemented to explore the effect of Ce doping on the electronic structure and optical properties of LaBr3 crystals using generalized gradient approximation (GGA) +U. And band structure, density of states and optical properties are discussed. Due to the transition of Ce3+ ion from 4f-orbital to 5d-orbital, the band gaps of LaBr₃:Ce (0.63 eV) is narrower than that of LaBr3 (3.569 eV), which produce more visible light in the same range of irradiated energy. Otherwise, the absorption spectrum (15.6 μm^-1) and reflection index (less than 12%) of LaBr3:Ce are smaller than LaBr3 (20 μm^-1, less than 15%, respectively), leading to transmit more visible light. The research shows reason that Ce doping can improve the luminescence performance of LaBr3 scintillators and the results are compared with the available experimental data.

The investigation focuses on analyzed the influence of periodic V-defects on wedge waves by laser ultrasound technique. Usually, wedge tip is almost non-perfect, which may bring in break and enormous economic losses. The wedge waveguide models with different periodic V-defects were established by using finite element method. We have observed multiple mode wedge waves in 20° wedge. The depth of defect is 0.1mm, and the periodic number are 1, 6, 12, and 24, respectively. Both reflected and transmitted waves are observed. And the low order reflected wave and transmitted wave modes separate from high order mode. As periodic number increase, the amplitude of reflected wave and transmitted wave decreased. By integrating the power spectra of the wedge waves, the energy distribution of these wedge waves of different periodic are analyzed. It is found that the energy has a fluctuation, which could be determined the location of defect. The energy has a gradually increase as the propagation before defect, and dramatic decrease after the defect. The results of this study can provide theoretical guidance for the positioning and size estimation of wedge defects.

We proposed a design of coherent fiber-optics-array collimator (CFAC) which is mainly composed of a single unitary collimating lens and prism. The CFAC system can be regarded as a “sub-aperture” of the whole fibers array in the tiledaperture scheme to expand combining channels efficiently due to its simple and compact structure. Then, we setup an experiment to verify the feasibility of the CFAC system with seven fiber lasers arranged in two dimensions and the CBC in 1064nm wavelength using single-frequency dithering algorithm is successfully achieved. By careful calculation, the residual errors among the laser beams are suppressed below λ/20 through an active-piston-phase control.

Based on angular spectrum expansion and 4x4 matrix theory, our works have combined the traditional vortex optical theory with the latest Topological insulator (TI) to present the reflection and transmission characteristics of an Laguerre Gaussian (LG) beam from a multilayered topological insulator slab. The reflected and transmissed beam intensities from three-layered TI slab are numerically simulated. It is shown that the distortion of intensity distribution is greatly affected by the topological magneto-electric polarizability of TI. The method presented in this article not only colud be extended to different TI-layers but could reveal unusual photonic band structures and band gaps in TI photonic crystals in further research.

Spot size is an important factor affecting the interaction between laser and single crystal silicon. Different radius millisecond pulsed laser is used to irradiate single crystal silicon. The effects of laser irradiation on large and small spot size, including temperature rise, damage area and damage morphology, are compared and analyzed. The influence rule of spot size on laser-induced single crystal silicon is determined and its mechanism is analyzed. The results show that the peak temperature of the laser irradiation center point is higher when the spot radius is 0.2 cm than when the spot radius is 0.1 cm; the damage area of single crystal silicon increases with the increase of laser energy density; the damage threshold decreases with the increase of laser spot size, and increases with the increase of pulse width.

We describe the design and experimental result of a LD pumped Nd:YAG laser with 12J energy at repetition rate of 10Hz. The temperature distribution was controlled to less than 2℃ on the surface by means of uniform pump and cooling. The ASE was calculated by energy storage code and fit well with the measurement results which was about 1.72 in average. The beam quality was controlled by means of mechanical design and adjustment and compensation by a home-made deforming mirror. The far field was measured to 3.23 TDL. The stability of energy and pointing were paid great attention and control by means of full absorption and high stability mechanical design. The energy stability was less than1%(RMS) and pointing stability was 73μrad(PtV), which made the laser very comfortable for use.

In this paper, in order to study the high temperature resistance of the transmission path of laser pyrotechnic system, the design of the high temperature resistant laser pyrotechnic system of the transmission path is designed. Combining with the design and research of the high temperature resistant multi-mode laser collimator, the high temperature resistant light energy transmission path is developed, and the laser energy transmission path through environmental test is used to carry out the system. The experimental results show that the high temperature resistant optical energy transmission path can make the laser pyrotechnic device fire normally after the high temperature test at 400℃ for 30 minutes and the mechanical environment test, which proves that the design of the high temperature resistant optical energy transmission path is feasible.

In this paper, the application of laser pyrotechnic device with dual seat single and dual state control function in airborne ejection escape system is studied. The system can meet the requirement of pilot's escape in emergency condition with two seats on board. The laser pyrotechnic device described in this paper takes the manual firing pyrotechnic laser as the ignition energy for the cabin life saving device, uses the optical fiber device to transmit the laser energy, designs the state selection switch for single and dual state control, and uses the laser explosive with different functions to realize the safety and life saving of the pilots in the left and right cabin. The device has the characteristics of novel structure, small volume, light weight, strong anti-electromagnetic interference, high safety and reliability, and is an ideal pyrotechnic device for the airborne ejection escape system in the future.

In this manuscript, a numerical model of laser array beams propagation through both turbulent atmosphere and shockwave layer is built. We have calculated the evolution properties of seven coherent laser beams projecting to a plane hypersonic target vertically. We utilize the angular spectrum propagation method with fast Fourier transform algorithm to simulate beam propagation through turbulent atmosphere. To the propagation through shock-wave layer, we first generate the density field and the refractive index field using dual-temperature model and Gladstone Dale formula, respectively. Then the corresponding optical path length and phase screen can be obtained. By analyzing simulated results, we find that the optical intensity distribution before and after through the shock-wave layer are almost the same but the phase distribution differences are significant and decreases almost linearly along the hypersonic flow direction. The phase difference indicates that the shock-wave layer will import a tilt aberration for the optical detection system installed in the hypersonic target.

As one of the earliest microwave absorbing materials (MAMs), carbon-based materials have been drawn the attentions because of their extensive sources, low density, simple preparation process and low cost. With the discovery of new carbon allotropes such as carbon nanotubes and graphene, especially the continuously improvement of microwave absorbing properties, carbon-based composites are expected to be applied as low frequency and broadband absorbing materials. In this paper, the latest basic research and application progress at home and abroad of carbon-based microwave absorbing composites such as carbon black-based composites, carbon fiber-based composites, carbon nanotubes-based composites and graphene-based composites are summarized. At last, the future direction of carbonbased microwave absorbing composites is introduced.

Laser damage is becoming more and more important part to consider in design of laser systems among these decade years, for high-power lasers are widely used in industry production, medicine, signal detection, and any other departments. There are two research directions of laser damage: one is the damage caused by ultra-short pulse, the other is that caused by ultraviolet beams. These two types of laser are usually combined to irradiate materials. Laser Induced Periodic Surface Structures (LIPPS) are special phenomena which can change many physical characters of materials, for example, surface absorptivity. LIPPS are usually caused by ultra-short pulse, as a step of laser processing. This paper will reveal the damage caused by ultra-short and ultraviolet beams, especially when they lead to LIPPS.

The world is confronted with increasingly severe challenges of unconventional threats with the popularization of small UAVs in civil fields. Due to the advantages such as killing or disabling targets with no or minimal collateral damage, the high energy laser weapon becomes one of effective means for coping with these kinds of threats. In order to guarantee cost-effectiveness, this paper presents an effect-based method for designing high energy laser weapons. First, we introduce the system components, the operating mechanism, and the damage capability of system. Second, we present the relationship equations between the on-target irradiance and all the influence factors. Finally, we discuss the laser selection problem and beam combining methods and show how to determine main technical parameters of the laser weapon system.

With the decreasing noise level of underwater vehicle, the infrared imaging characteristics of underwater vehicle wake become one of its main detectable sources. Using the infrared characteristics of underwater vehicle wake to remote sensing detect the traces of underwater vehicle has gradually developed into a new detection method. Because of the high contingency and large error in judging underwater vehicle wake artificially, it can be overcome by using deep transfer learning to identify and locate the wake. This paper focuses on the infrared feature recognition of underwater vehicle wake with deep transfer learning, and wake sample sets of different classes are produced by image classification. The training effect of different pre-training networks is compared by using deep transfer learning. The influence of internal parameters of pre-training networks on the training effect of wake is discussed. Finally, combined with Faster-RCNN algorithm, the identification effect of wake is tested. The final recognition accuracy is ideal. It has certain application potential for future research on wake remote sensing detection combined with convolution neural network identification.

High speed railway vehicle bogie is welded together with steel plate and tube. T joint and butt joint are the main types traditionally welded with gas metal arc welding (GMAW) method. In hybrid laser-arc welding process, laser interacts with the arc to form a stable composite welding pool, which significantly increases penetration depth. In this paper, the hybrid laser-arc welding process of S355, which is the commonly material of bogie, with 12mm thickness T joint without groove was studied. The laser optical axis and the welding wire axis were designed in different planes, and hybrid laser-arc welding parameters of the fully penetration t-joint were developed by orthogonal test. Four parameters were designed as orthogonal factors, which were welding position, laser incident angles, shielding gas flow rate, laser power. Typical defects modes and the causes were summarized, which were using as standard evaluation. The evaluation scores were obtained from the appearance and internal quality of test welds. Experiments show that welding position has the most significant influence on the forming stability of back welds; the laser incidence angle and the laser power have obvious effect on the fusion defect. The shielding gas flow rate has influence on internal and surface pore. Finishing orthogonal test, the optimized process parameters of 12mm thickness full penetration welds in T joint without groove were obtained. One-side welding with back formation was achieved soundly and stably, and the back fillet welds size was greater than a3.

To minimize the effect of thermally-induced distortion and avoid the reabsorption phenomenon caused by the atomic alkali inside an alkali vapor cell (generally several or several ten millimeters long) in a diode-pumped alkali laser (DPAL) system, a novel concept of thin-disk DPALs in which alkali is sealed in a symmetric thin-disk cell has recently been proposed by referring a solid-state thin-disk laser. In this paper, we construct a theoretical model to study a V-pumped thin-disk DPAL system where the pump beam propagates along a V-shaped path. The influence of the thickness and the radius of a thin-disk cell, the incident angle of a pump beam, and the cell temperature on the output features of a thin-disk DPAL is studied by employing this model. In addition, we also investigate the effects of the profile of a pump beam such as a flat-top beam or a Gaussian beam on the uniformity of the temperature distribution and output power of a thin-disk DPAL. It has been demonstrated that a V-pumped DPAL might be better than an end-pumped DPAL. With respect to the uniformity of temperature distribution at the end-windows of a cell, the results reveal that a flat-top beam holds out a considerable merit compared with a Gaussian beam.

High brightness broad area lasers with high polarization purity are highly efficient light sources for high brightness fiber coupled and direct semiconductor lasers. Effect of lateral index step on the performance of high-power broad-area 970-nm diode lasers based a large-optical-cavity waveguide structure was studied and presented here. The index step of the 80-μm wide ridge is found a key parameter to control the output power, lateral far-field angle, beam waist and polarization purity. The threshold current decreases with the increase of the etching depth while the slope efficiency increases. When gain guide lateral waveguide by very shallow etching was used, the beam waist expands to a size of more than 200 μm, which was attributed to anti-guiding effect and current spreading. When large index step is introduced by deep etching, enhanced filamentation was observed, which is attributed to an enhanced confinement of the higher order modes. What’s more, the strain introduced by the etching of the ridge can deteriorate the polarization purity. The study in this paper shows that the lateral index step should be optimized to fabricate high brightness high efficiency broad area lasers with high polarization purity.

We investigate both theoretically and numerically the Airy-Talbot effect for a superposition of fundamental Airy beams with initial launch angles and a lateral deviation between each other in dynamic linear index potentials. Our results show that the Talbot length are same in both free space and dynamic linear index potentials, the accelerating trajectory of Airy- Talbot effect can be manipulated effectively by both the linear potentials and initial launch angles effectively. In other word, by adjusting the index gradient and initial launch angle, this self-imaging can propagate along some predefined trajectories. Theoretical results agree with the numerical simulations very well.

A focus tunable micro-lens based on electric field-refractive index modulation in Ag nanoparticle doped polymer dispersed liquid crystal is designed and verified based on finite element method. The micro-lens, with diameter and rise of 60 and 20 microns, consists a pair of ring-type electrodes with polymer dispersed liquid crystal sandwiched between them. By adopting the experimental electric field modulated refractive index, a finite element model is developed to investigate the physical coupling mechanism among electric field, refractive index, electromagnetic fields as well as the focus. Results show that non-homogenous refractive index within the lens is modulated due to the enhancement of electric field, and the refractive index has a negative correlation with the electric field strength. It is also found that the focal distance linearly increases within 115~128 μm when excitation voltage changes within 40 ~220 V with sensitivity of 0.09 μm/V. A critical voltage of 40 V, corresponding to gate electric field strength of 1300 kV/m is founded, which may attribute to the refractive difference between the polymer base and liquid crystal. In comparison with mechanical and geometric focus adjustable lens, such electric field tunable focus micro-lens is advanced in rapid response, high reliability and high accuracy, which enable its promising applications in semiconductor lasers, micro-optical devices.

A point-by-point long period fiber grating inscription by using femtosecond photonic crystal fiber laser with high repetition rate has been studied experimentally. A fabrication platform was designed and built up, which was composed of a laser focusing system, a real-time imaging observation system and a precision three-dimensional positioning stage. In order to ensure quality of the fabricated fiber grating, the machining process was real-time monitored using a CCD camera and the transmission spectrum was real-time measured using a spectrometer. To reduce manual error in operation, a control program was coded by self-written LabVIEW program, which can realize the synchronous control of the 3D micro-positioning platform and the electronic high speed shutter. In the experiments, the femtosecond laser came from a high-power large-mode-area Yb³⁺-doped photonic crystal femtosecond fiber amplifier system, delivering laser pulses with an maximum power of 18W, a pulse width of 66.5fs, a central wavelength of 1040nm, and at a repetition rate of 52MHz after pulse compression. Fiber gratings with the duty ratio of 1/2 and the period of 400μm have been fabricated by point-by-point inscription technique. The measured transmission spectra indicate that the fiber gratings have good spectral properties. The experimental result exhibit the good micromachining ability of femtosecond photonic crystal fiber laser, which will lead to more and more applications in the future.

The high pressure loss and low heat transfer efficiency have been plaguing the development of high power fast axial-flow CO₂ laser. In order to solve this problem, a special longitudinal vortex generator (LVG), which contains two modified right-angled trapezoid wings and interrupt gap (TMRTW), was proposed. The performance of a single trapezoid winglet (STW) and TMRTW was discussed. Numerical study reveals that compared with STW, the TMRTW has better flow and heat transfer characteristics under the same initialization conditions. Further parametric study indicates that the TMRTW generates vortex. The intensity of this vortex is mainly present in central area. The downstream extension of this vortex is better than that of STW. Especially for the developing of boundary layers, this is beneficial. Hence, the performance of heat transfer for TMRTW is enhanced obviously with Re less than 1200. Compared with STW, the heat transfer for TMRTW is enhanced by 16% under the optimized structure size, with the pressure penalty almost the same.

We theoretically study the photoelectron momentum distributions of the negative hydrogen ions by a pair of time-delayed circularly polarized laser pulses. It is found that the multi-arm helical vortex structures appear in the photoelectron momentum distributions. Moreover, the vortex structures can be adjusted by the laser parameters. The present work is meaningful for the optical control of the laser-induced detachment of negative ions.

The pulse shape from the pulsed amplifier always distorts because of gain saturation effect, an effective method is active control the output pulse shape by reshaping the pulse shape of the laser seed. We demonstrated a new method for active temporal pulse shape control of fiber amplifier with adaptive proportional control. We numerically researched three proportional control methods, including static proportional control, adaptive proportional control and piecewise adaptive proportional control. The results show that proportional control can generate arbitrary temporal pulse shape with high accuracy and less iterations even if parameters of the fiber amplifier are unknown.

The angle-based intersection measurement system is a high-precision overall measurement network based on the perspective observation in space. However, when the target is moving, the angular intersection failure will cause dynamic error to limit its application in the field of dynamic measurement. Aiming at this problem, Firstly, this paper analyze the sources of dynamic error from the principle, studies the influencing factors of system dynamic error include :the motion state of the measured object, station deployment. Secondly, constructs a mathematical model to predict the dynamic error of the measurement system. Finally, design some simulation experiments to quantify the measurement dynamic error at different measure conditions. The results show that under the measurement conditions of the measurement area is 10m x 10m x 1m, observation angle uncertainty is 2′′, the measured target moves at 0.05m/s, the average dynamic error of the measured area under the 0_4 deployment is the minimum, and value is 0.25mm.

Transceiver collimator is an advanced component in high power fiber lasers long distance transmission. Here, based on fiber weak taper technology, an all-fiber laser emitting and target detecting transceiver collimator is proposed. Meanwhile, a (18+1)-channel optical fiber bundle detection experiment was succeed build.With a home-made signal processing circuit, the on-line dynamic tracking image display was achieved, and the target detection and transceiver collimator was experimental demonstrated.

Laser sources have been well adopted in spectrophotometry and optical materials measurements with excellent advantage of high spectral output power and hence large signal-to-noise ratio compared with traditional lamp sources. However, continuous wave lasers normally have very small tuning spectral range, due to either the limited bandwidth of the gain profile or low conversion efficiency due to the limited amount of pump power. Pulsed laser sources can be generated via nonlinear processes such as optical parametric oscillation or amplification and so on to cover a wide spectral range. For instance, supercontinuum laser sources have been developed with above 1 W/nm collimated spectral power over the visible to mid-infrared range. The output of the supercontinuum laser sources can be extended to cover UV range via second harmonic generation. Normally the spectral bandwidth of the output can be from tens to thousands nm and a monochromator or its equivalents can be used to select or tune the desired working wavelengths. The repetition rate of the laser sources can be from a few Hz to more than 1 GHz, with reduced pulse interval and efficiency due to more distributed pulse energy and hence peak power. A pulsed laser source with an original pulse width of ~ 130 fs, a repetition rate of ~ 80 MHz, and the spectral range from 280 to 2000 nm is applied for spectrophotometry calibration and research works have been devoted to converting the pulsed laser into continuous wave in order to improve the measurement linearity. Optical fiber bundles were used to divide each laser pulse into hundreds of small pulses via different optical path length and then recombine them for a temporally further distributed pattern. Two different types of optical fibers were adopted for the bundle, one for 280 nm ~ 700 nm wavelength range, and the other for 700 nm ~ 2000 nm. The numerical aperture of the optical fiber is 0.22 and the core diameter is ~ 200 μm. Each bundle has 100 pairs of optical fibers with different lengths. The refractive indices were extrapolated over the wide spectral range and used to calculate the optical fiber lengths for uniform time interval after recombination. The optical losses of the optical fibers over the wide spectral range were evaluated. After taking the spectral optical losses, fiber lengths, and input beam spatial power distribution into account, the arrangement of the optical fibers with different lengths at the input terminal was optimized for overall high performance over the two desired working spectral range. The time interval, relative power, spatial distribution of the distributed pulses throughout the designed optical fiber bundles were validated using a highspeed photodetector and oscilloscope. The optical fiber bundles can be useful for a variety of spectrophotometry calibration and optical materials measurement works using pulsed laser sources.

A novel method for active coherent beam combining by Particle Swarm Optimization (PSO) algorithm is demonstrated in this paper. The principle of this method is introduced, and its advantages are presented in detail. In the simulation, 37 fiber lasers are coherently combined by employing stochastic parallel gradient descent algorithm with 91 steps, and then, the combined beams are combined by PSO algorithm with only 30 steps. And the result shows that the more laser elements, the more remarkable PSO algorithm is in the CBC system. Because of the high control ability of PSO algorithm in coherent beam combining combined with traditional algorithm, it is scalable to phase-locking system in a large number of fiber lasers.

This paper presents magnetic-field-assisted femtosecond laser drilling of bone with deep drilling depth, good surface quality and high removal rate. In this study, the feasibility of producing deep cavity under magnetic field condition is investigated. When magnetic field is introduced, the depth of drilling hole is increased from 236μm to 483μm, and the removal rate is increased from 3.04×10^-3 mm³/s to 5.46×10^-3 mm³/s. Moreover, no thermal damage including carbonization is observed during laser drilling process.

In this paper, a new single photon laser data processing method is proposed and coarse -to-fine denoising strategy is adopted. Global and piecewise denoising based on the frequency histogram of photon elevation is the first step and direction self-adaptive fine denoising is the next which calculates density value, and uses self-adaptive elliptical LDBSCAN (A Local-Density Based Spatial Clustering Algorithm with Noise) algorithm to effectively remove the noise distributed around the signal segment. Experiments using MABEL (Multiple Altimeter Beam Experimental Lidar) data is implemented and the results validate the proposed algorithm which can effectively extract signal photons from high background noise, and has more reliable results than MABEL official to some extent.

This paper mainly studied the structure of high power pump combiner. Pump combiner is one of the key components of high power fiber laser and fiber amplifier. The ability to conduct high power of pump combiner is often influenced by the heat dissipation structure. The faster the heat dissipates the higher power the combiner conducts and the higher power fiber laser the combiner can be applied in. We made a pump combiner with the help of a conical quartz tube and the heat dissipation structure of the combiner can send away the lights that the combiner leaks so that the heat accumulation in the combiner can be avoided. The experimental result shows that when the pump power reaches 3000W the temperature of the combiner is about 28℃ which indicates that the heat dissipation efficiency of the structure is high.

This paper mainly studied the tensile strength of the splicing point of optical fibers. We analyzed the main factors that influence the tensile strength of the splicing point during the process of fiber splicing and post processing. The results demonstrate that it is the expansion of little cracks produced during fusion process that decreases the tensile strength of splicing point. We eliminated the cracks on the splicing point by using CO₂ laser based on the principle of crack production and elimination. The experimental result shows that after eliminating the cracks the tensile strength of the splicing point is observably improved and it reaches more than 160kpsi.

The 30Cr3Ni2 alloy steel samples were prepared by direct laser deposition (DLD) technology with different scanning speeds. The microstructure and mechanical properties of the samples were studied by metallographic microscope, scanning electron microscopy, energy dispersive spectroscopy, microhardness tester and electronic universal material tester. The results show that when the laser power was 2500W and the scanning speed was 10mm/s, the fabricated sample mainly consisted of granular bainite(GB) with (Fe,Cr)₇C₃ carbide. The average hardness value was 341HV, the tensile strength was 875Mpa, the yield strength was 867Mpa, and the elongation was 3.9%. This study provides the basis for the further development of alloy steel produced by DLD.

Based on the fretting wear failure of key parts of short stress line rolling mill, selective laser melting was chosen to repair the failure parts. The effect of laser scanning rate on microstructure, hardness and wear resistance of cladding layer was studied. The results show that the microstructure of the cladding layer is mainly lamellar martensite with a little retained austenite and carbide. The hardness of the cladding layer increases with the increase of scanning rate and the decrease of energy density. The maximum hardness is about 950 HV_0.2. The friction coefficient of the cladding layer varies little with different laser scanning rate. The wear rate of the cladding layer increases firstly and then decreases with the increase of laser scanning rate. The wear rate of the sample with scanning rate of 6 mm/s is the smallest, which is 2.0466•10^-5 mm³/(N·m) .

Effect of different TA15 powder additions on high temperature oxidation kinetics of pre-laid laser melting 45CrNiMoY alloy steel was studied. Thermogravimetric method was used to determine the kinetics curve of constant temperature oxidation of alloy steel sample at 700℃. The results show that bainite and acicular ferrite are the main microstructures of alloy steel after adding TA15 powder. With the increase of TA15 powder, the microstructures showed a distinct trend of refinement. The oxidation kinetics curves of alloy steels follow the linear law. The alloy steels with 1.0 wt.% TA15 powder have the best resistance to high temperature oxidation, and the oxidation rate constant is 1.48×10^-4 mg²·cm^-4·h^-1. Particle reinforcement phase formed in alloy steel can provide pinning effect for oxide film, while micro-cracks added in excess TA15 alloy steel sample are not conducive to the improvement of high temperature oxidation resistance.

Additive manufacturing (AM) enable new and innovative design forms that cannot be produced by conventional manufacturing methods. Space optical instruments are precision systems that require high resolution, light weight, low cost and short schedule. Metal AM technology is more adept to the fabrication of mirror blanks and support structures with complex shapes. In this study, selective laser melting (SLM) technology were utilized to create workpieces. The AlSi10Mg mirror blanks were fabricated with metallic powder bed fusion. After forming, post annealing process at 300 ℃ for 2 h was performed to relieve internal stresses. The microstructure of AlSi10Mg produced by SLM is compact, and the mechanical properties are much higher than the alloy formed by conventional casting. The single point diamond turning (SPDT) was been applied to deliver optical quality mirror. The surface characteristics of AM components have been measured. The turning surface meets the 8~11nm RMS and 1.05λ PV. This research can be used for the manufacturing of lightweight space optical mirrors and improve overall process efficiency.

In this paper, a simple and effective tunable multi-wavelength ytterbium-doped fiber laser (MWYDFL) is proposed and demonstrated. A nonlinear polarization rotation (NPR) structure, including polarization controller (PC) and polarizationdependent isolator (PDI) is used as the wavelength selector and works to generate intensity-dependence transmission to suppress the mode competition and solves the problem of greater intensity of side modes. Thus the stable all-fiber ring cavity structure is realized. Through controlling and adjusting the polarization of the PC in the cavity, a multiwavelength and tunable single wavelength laser with good performance is achieved under the room temperature. The laser outputs of the single-wavelength can be tuned about 12 nm with an interval of about 1 nm from 1074.42 nm to 1090.97 nm. The side-mode suppression ratios (SMSRs) and the linewidths of these lasing lines are all over 50 dB and less than 0.02 nm. Single-wavelength, dual-wavelength, triple-wavelength and quadruple-wavelength can be switched by appropriately adjusting the PC. The power fluctuations and wavelength shifts are less than 2 dB and 0.02 nm in an hour at room temperature.

Morphological evolution of ripple on nickel surface induced by temporally shaped femtosecond laser irradiation were studied and compared with titanium. It was revealed that the transformation of single-pulse irradiation into double-pulse irradiation can exert very different influence on ripple morphology evolution for different metals. For nickel, the double-pulse irradiation resulted in the growth in rippled area, ripple period and ripple contrast, compared with the single-pulse irradiation, while double-pulse processing of titanium leads to reductions in in rippled area and ripple period. The contrasted influence of T_e on electron-phonon coupling factor (G) for the two metals was the primary factor for the different behaviors of ripple morphology evolution with temporal pulse shaping.

This work presents for the first time a study of a fibre laser mode-locked due to a carbon-nanotube-based saturable absorber whose parameters could be controlled by a joined action of optical radiation and electric field. Combination of different types of control (optical and electrical) allowed variation of dynamics of the saturable absorber parameters and greater choice of pulsed generation regimes.We demonstrated the possibility of live switching of laser generation between various pulsed regimes through combined electro-optical action on the polymer-free carbon nanotube film.