This PDF file contains the front matter associated with SPIE Proceedings Volume 11849, including the Title Page, Copyright information, and Table of Contents.

Target alignment technology is one of the most critical technologies in high-energy physics experiments, and is an important technology related to the success of the laser fusion experiment. This paper describes the error in the basic target alignment scheme, and designs a series of alignment fiducials around the target to achieve the improvement in target alignment precision. This paper analyzes the influence of fiducials-group’s forms on the target alignment error. According to their respective properties, under the constraints of the experimental conditions, and combined with the linear and nonlinear fiducials-group’s design, improvement of target alignment precision and error transfer are achieved. Under the experimental requirements of the SG-II-U facility, combined with the working conditions, a surrogate target with alignment fiducials-group is designed, and through the interaction of the fiducials-group and the alignment mark in viewers, the error of target recognition can be greatly optimized and the uncertainty of target alignment can be reduced.

In inertial confinement fusion laser device, the disposable debris shield is necessary to protect expensive optical elements from the contaminations of target debris when high-energy PW laser was focused in the terminal focusing system. While the shield plate will have a very important impact on the focusing quality. In this paper, the design of debris shield, in high-energy PW focusing system, is studied by optical transmission theory, and the design parameters, such as PV value of wavefront, thickness and installation position of shield plate, are optimized. If 95% of the focal spot energy is concentrated within 10DL, the B-integral introduced by the debris shield should not exceed 8.5 rad when the plate is placed at 0.1f from the parabolic mirror. When the laser power is 1PW, the installation position of 3mm shield cannot exceed 0.29f. The influence of wavefront PV value on energy concentration of focal spot is little. A 3mm shield plate has good damage resistance on light field modulation when its size over 350μm. And the thinner the thickness is, the better the resistance is. This work is important for the arrangement and optimization of disposable debris shield in high-power PW laser focusing system.

We numerically generalize the nonlinear propagation Schrödinger equation by introducing contribution (to the nonlinear refractive index variation) factor α , only for the numerical investigation of the higher-order Kerr effect (HOKE) with the higher-order Kerr nonlinear coefficients (n₄, n₆, n₈). Our results confirm that the uncertainties of the higher-order Kerr nonlinear coefficients have a non-negligible effect on propagation of the intense femtosecond laser pulse in air, when the HOKE is considered. The smaller the α the larger the defocusing that is caused by HOKE, and the weaker the clamping intensity, and the remoter the position where the filamentation starts, and the longer the length of filament. Moreover, the higher-order Kerr terms play a role before the plasma defocusing, if the HOKE is considered.

A preliminary concept design of a diode pump solid-state Nd: glass laser amplifier based on helium-cooled multi-slab geometry is presented. The laser amplifier is designed to obtain an output of 100 J/10 Hz. The gain slabs applied in the laser amplifier can lead to low thermally induced wavefront distortion, which are based on heating the edge by the cladding layer. In addition, we also develop a comprehensive numerical model for study effect of amplifier spontaneous emission on the stored energy and thermo-optic effects in the Nd: glass laser amplifier. The results of simulations show that energy storage efficiency of 48% and the average volume density of the stored energy greater than 0.55 J/cm³ are obtained for the laser amplifier. The wavefront distortion can be decreased to 0.78 λ for a gain slab in the laser amplifier.

In order to reduce the influence of thermal lens effect on beam quality of the multi-pass laser amplifier, a new method of spherical-aberration self-compensation based on ZEMAX physical optical simulation is proposed. Firstly, the change of quality of gaussian beam after passing the thermal lens is simulated according to the principle of geometric optics. And the simulation results show that if two identical thermal lenses are placed symmetrically near the focal point of the laser beam, the degradation of the beam quality caused by the first thermal lens can be compensated by the second thermal lens. Secondly, a four-pass laser amplifier based on the spherical-aberration self-compensation theory is designed by the sequence mode of ZEMAX software. Finally, according to the theoretical model, we design a picosecond fiber-solid hybrid laser amplifier which is seeded by an all polarization-maintaining (PM) fiber laser. The output power of the all PM fiber laser is 2 W. After the solid-state amplifier, the final output laser power reaches 8.5 W with M² factor of 1.2. The beam quality is well preserved by the four-pass amplification structure which is favorable to the spherical-aberration compensation. This system, which combines the advantages of the all PM fiber amplifier and the solid-state laser amplifier, enables high repetition rate and good beam quality with high gain picosecond pulses. It makes significant contributions to many applications such as material micro-processing, laser ranging and laser detection.

The triple-foil target irradiated by the counter-propagate(C-P) laser has been proposed to enhance the laser to X-ray conversion efficiency (CE). Through one-dimensional radiation hydrodynamic simulation, it is found that the total X-ray CE for the triple-foil target with C-P laser has a 61% radiation energy fraction. It is a 6% improvement compared to the double-foil target and a 17% improvement to the standard target. It has been shown that the increased X-ray emission is mainly concentrated in the soft X-ray region, which is caused by the broad radiation region and reduces the development of the ion kinetic energy. Additionally, the target geometric parameters have been discussed for finding the best laser to Xray CE with the detailed analysis of the plasma's hydrodynamic evolution.

In this paper, we present a quantitative mathematical model of Foucault test that we have developed which mainly use the method of light trace-out, and show how this model works with an X-Y axis automation module and digital grams processing to aid quantitative optical mirror testing. We also present our verification work through building up a new Foucault test instrument system and show the testing result about a finishing product-a small diameter sphere mirror. Additionally, we verify the method by simulation work and counterpart testing result of interferometer. Through the work, we want to develop an easy-to-conduct method of efficiency optical surface wavefront errors testing which use limited optical images with location information to solve the target image and a much cheaper quantified optical-testing-instrument solution than traditional and general method of laser interferometry instrument.

As an important component of space environment, the ionospheric plasma is the main background environment for the operation of low-orbit spacecraft. The study of ionospheric plasma environment parameters and the enrichment of plasma environment data are beneficial to improve the reliability of low-orbit spacecraft operation. Langmuir probe is the most popular method for detecting the plasma parameter of ionospheric, however, it has some defects. In this paper, we design a plasma generator based on radio-frequency discharge to imitate the ionospheric plasma environment, and measure plasma parameter based on Thomson scattering by import a Nd: YAG laser oscillate in the plasma generator. The result demonstrates that the intensity of laser Thomson scattering signal is positively correlated with the change of plasma electron density. The electron density in the plasma generator is calculated according to the laser Thomson scattering signal intensity, and the error is less than 10% compared with that measured by the Langmuir probe.

The available information which is sharply increased requires a long time-period and high-capacity preservation method. In this paper, we proposed a method to preserve miniature image in stack structure. A large number of information images with a minimum pixel size of 200 nm were transferred to an AIST thin film using a laser directly writing system. After clearness, the information region was retained and the non-information region was removed. The single-layer information region samples with a thickness of 0.15 mm have high contrast and high transmittance. After being stacked and packaged into a 52-layer structure, each layer information image can be read out directly by an optical microscopy. The tolerance of the material to acid, alkali, and temperature is tested, and the results show that this method has excellent information preservation performance. This work provides a promising solution for future information preservation.

High-efficiency and broadband OPCPA is one of the methods to achieve multi-petawatt or even hundreds petawatt laser system.We demonstrate broadband OPCPA centered near 800 nm in 3D space of YCOB. A maximum conversion efficiency of ~15% and compressed duration of 30.6 fs are achieved for two types of YCOB crystals with PM on the principal and non-principal planes (NPP). The amplified energies and conversion efficiencies of different PM angles confirm that the effective nonlinear coefficient (deff) on the NPP is much higher than that on the principal plane (PP). It is worth studying on PM in 3D space to support higher deff, wider amplification bandwidths, and gain wavelength ranges that cannot be amplified on the PP of nonlinear crystals. OPCPA in the 3D space of nonlinear crystal can be used as amplifiers in petawatt scale or few-cycle high-power laser systems.

Here, we report a pulsed 1135 nm all-fiber gas Raman laser based on hydrogen-filled hollow-core photonic crystal fibers (HC-PCFs). A high-pressure all-fiber gas cavity is fabricated by fusion splicing HC-PCF and solid-core fibers. Pumped with a nanosecond 1064 nm fiber amplifier, 1135 nm Stokes wave is generated by rotational stimulated Raman scattering of hydrogen molecules.

The frequency domain optical parametric amplification technology, as a new technology reserve for ultra-strong ultrashort pulses of 10 PW or even EW-level OPCPA systems, has many advantages in achieving high-energy ultra-wideband OPCPA. It can take the large gain bandwidth into consideration while enlarging the energy of ultra-short pulses, does not need stretcher and compressor, and is not restricted by materials such as crystal growth and grating damage threshold. In this thesis, the theoretical analysis and numerical simulation of frequency-domain chirped-pulse parametric amplification (FOPA) are mainly performed to complete the entire system design and experimental verification. Based on the picosecond laser system in the laboratory, the experimental verification of the frequency-domain optical parametric chirped-pulse amplification technology with a center wavelength of 800 nm and a gain bandwidth of nearly 100 nm has been completed.

In this paper, the physical model of the coherent polarization beam combination (CPBC) system is established by using Jones-matrix mathematics, and then the coherent-adding mechanisms between the sub-beams in temporal, spatial and spectral domains are analyzed. The intrinsic relationship between optical-field coherence decay and beam misalignment is established from temporal domain (optical-path deviation, phase-locking residual), spatial domain (beam-pointing deviation, spot-overlapping deviation, spot-width error) and spectral domain (B-integral imbalance, dispersion imbalance, central-wavelength drift, spectrum-width error) respectively. Furthermore, the dependence between the combining efficiency and the individual experimentally-measurable misalignment is quantified using numerical simulation, and the error tolerance of the each factor is calibrated separately for efficient combination, which provides quantitative guidance for the practical system. The results of this paper can be applied to the analysis of cascade extended array CPBC system after proper mathematical extension. In addition, this study also provides a feasible quantitative analysis method for the degradation of optical-field coherence between coherent beams, which can be applied to other research fields that require optical coherence management.

Hollow-core fibers (HCFs) provide an ideal environment for the interaction of light and gases, which gives birth to a novel kind of lasers, namely fiber gas lasers (FGLs). Although there is a rapid development of FGLs in the past years, highly efficient and stable coupling of the pump light is still a key limit for their applications in the future. Here, we propose and fabricate the HCF end-cap for the first time. The measured results show that the HCF end-cap can bear several hundreds of watt laser power, and the coupling efficiency is around 70%. This work opens new opportunity for the development of high-power FGLs.

Lasing from HBr-filled hollow-core fiber (HCF) based on population inversion is demonstrated and characterized. Usually, there are two emission lines corresponding to each absorption line. Here, by controlling the gas pressure in the HCF, a single emission line P(7) of 4.26 μm is efficiently achieved when pumping with line R(5) of 1958 nm, and the other emission line R(5) of 3.91 μm is totally suppressed. The maximum 4.26 μm laser output power of 350 mW is obtained with a slope efficiency of about 11%.

In this paper, we have studied the method of optimizing the coupling efficiency of the (2+1) ×1 combiner under the condition of large NA pump light injection. After optimization of the taper length of the pump fiber, the coupling efficiency of the combiner is increased to 97.3% from 91% with 1870 W pump light (NA=0.19) injected, and the temperature characteristic is improved from 24°C/kW to 16.6°/kW, which could offer some useful instructions for the fabrication of the side-pumping combiner for high-power fiber laser applications.

Fiber tapering technology has been used to realize low-loss coupling from solid-core fibers to antiresonant hollow-core fibers (AR-HCFs) at low-power level, by inserting the tapered solid-core fibers into the hollow-core of AR-HCFs. Here, we have demonstrated the high-power coupling capacity of this way. For ice-cream type AR-HCF, a transmission efficiency of ~47% is achieved with injected 1080 nm laser power of ~90 W in a ~2 m HCF; for nodeless type AR-HCF, a transmission efficiency of ~40% is achieved with injected 1550 nm laser power of ~32 W in a ~2 m HCF. The output mode field with good beam quality shows the mode filtering characteristics of AR-HCFs.

In this paper, mode distribution in large-mode-area (LMA) 25/400 fiber was investigated while attempts to recognize and sort different modes with their combination were carried out on a CNN net via Tensorflow. VGG16 model was chosen as the backbone net through several test to increase precision. The model was trained on a dataset including 6000 pictures in 15 categories. And the final accuracy was up to 0.98. It indicates that recognizing modes in high power fiber laser system based on a CNN net was a feasible plan in the mode control assignment.

Fiber Bragg Gratings (FBG) have great significance in the development of high-power fiber laser systems. Fabrication sources, fibers, and fabrication technology would affect the performance of FBGs directly. In this research, a scanning exposure method for fabricating FBGs in different types of photosensitive fibers with a 213nm solid-state laser source was proposed. The Q-switched Nd: YVO4 laser fifth harmonic source was compared with the traditional excimer lasers and the impacts of lengths, center wavelengths, titled angles, and apodization on the reflection and transmission spectra of FBGs were discussed. The scanning fabrication system, which can realize the tilting of phase mask and the adjustment and monitoring of tension, was built according to the characteristics that the output spot diameter of the fabrication source was sub-millimeter. While the high quality of fabrication was guaranteed, FBGs with lengths of 3mm~20mm, center wavelengths shift of 0nm~4.2nm, and tilted angles of 0~21° were obtained, and all the parameters were simultaneously adjusted and controlled, the deepest transmission loss of about -70dB. FBGs fabricated were of good stability and repeatability, especially in hydrogen fibers whose stability was independent of high-temperature annealing (1500°C) which was different from the fabrication results of excimer laser sources. Then the unconformity between experimental results and theoretical simulation was discussed and the optimization schemes were proposed. The experimental results and analysis provided a better experimental scheme for UV laser fabricating FBGs and the experimental basis for further optimizing the fabrication technology and further analyzing the microscopic mechanism of optical fiber photosensitivity.

In this paper, a broadband microwave photonic channelized receiver based on optical frequency comb (OFC) injection locking technology is illustrated. The simulation results show that, with more than 80 comb lines generated from OFC, this receiver enables channelized scanning and reception of broadband signal up to 40 GHz with instantaneous bandwidth of 1 GHz. Meanwhile, the channels selected using optical injection locking (OIL) technology, perform high gain and low phase noise with suppression ratio between the selected comb line and other comb lines is 28.7 dB. Due to OIL technology, the wideband tunability of this receiver would not depend on the optical filter or demultiplexer, and the band limitation and operation resolution introduced by optical components are broken through. The OIL technology also lead to the architecture of receiver more compact and feasible in practical.

A four-pass MOPA laser with tunable pulse width ranging from sub-nanosecond to nanosecond is presented in which a laser signal with the initial-transmission-controlled tunable pulse width is magnified by a four-pass laser amplifier. By the use of the MOPA system, a laser pulse energy over 1 J and pulse width ranging from 545 ps to 1464 ps were obtained.

Chirped and tilted fiber Bragg gratings (CTFBGs) have attracted a lot of attention for stimulated Raman scattering (SRS) suppression in high-power fiber laser systems in past years. Here, we fabricate CTFBGs in large-mode-area double cladding fibers and demonstrate its application in a 2-kW fiber laser for SRS filtering at the system’s output. A maximum Raman suppression of about 17 dB is obtained at the central wavelength, and the insertion loss is smaller than 0.2 dB for signal laser. In addition, no obvious degradation of laser beam quality is observed. Better suppression effect could be achieved by broadening the rejection bandwidth of the CTFBGs in the future.

The one-stage master oscillator power amplifier (MOPA) is an efficient way to acquire high-power narrow-linewidth fiber lasers (NLFLs), which have wide usage in beam combination and detection. However, stimulated Raman scattering (SRS) is still one of the main obstacles for further power scaling. In this paper, we set up a counter-pumping kW-level narrowlinewidth one-stage MOPA fiber laser system and tried to use a chirped and tilted fiber Bragg grating (CTFBG) as a broadband rejection filter to suppress the Raman stokes light in the output laser. We finally acquired a 2.5 kW output with 3 dB linewidth of about 0.87 nm, and the SRS isolation ratio is ~42 dB on the spectrum, which is 12.7 dB higher compared with the situation without CTFBG.

In this paper, we fabricate FBGs-based FPCs using femtosecond laser and the temperature characteristics is studied. The FBGs are inscribed by line-by-line scanning technique, by which the FBGs can be limited to a specific area in the fiber core region. Besides, the grating length, the grating position and the distance between two successive FBGs can be precisely controlled to adjust bandwidth and free spectral range. FP interference is obviously seen in reflection and transmission spectrum. Line-by-line inscribed FPC is a good candidate for sensing application.

In this paper, based on a full vector-diffraction theory, we present a systematic investigation of the characterization of tight-focused vector fields formed by an off-axis parabolic mirror (OAP), and discuss the effects of offset of an OAP, polarization of light and parabola f-number on the focused field properties by an OAP used with a perfectly aligned beam. Furthermore, we demonstrate a configuration optimization process of an OAP, and obtain an optimum OAP configuration scaling rule which makes it possible to achieve the maximum peak intensity. In addition, we explore the electromagnetic field behaviour in the focal plane at four characteristic times of an optical cycle we explore the electromagnetic field behaviour in the focal plane at four characteristic times of an optical cycle and the dependence of the direction and the amplitude of the focused electromagnetic field on the incident polarization, the offset, and the parabola f-number. we also carry out an assessment analysis of the critical misalignment angle corresponding to a 10% drop of the maximum focused peak intensity. Understanding these effects and scaling laws is of great significance to enhance the focusing performance of OAP in the optimal configuration, especially for the structural design and selection of OAP in ultrashort and ultraintense laser-matter interaction experiments.

We present a coaxial laser metal deposition (LMD) system based on the single mode laser. The influence of input beam diameter on the ring spot properties such as spot shape, filling factor and ring width are investigated through numerical simulation. The result shows that the smaller ring spot and narrower ring width can be obtained by adopting the single mode laser in the coaxial LMD system, compared with the traditional coaxial LMD system based on the multimode laser (Flat-top beam). This also indicates that our system has advantages in the application of high-precision additive manufacturing (AM).

The average output power of fiber laser oscillators can stabilize in very high levels reaching kW within the recent years. However, a further scaling is limited due to some nonlinear effects, one of which is simulated Raman scattering (SRS). Here we propose a CO₂ laser pulse inscribed transmission long period fiber grating (LPFG) in large mode area (LMA) fiber and employ it within a fiber laser oscillator to mitigate SRS. The wavelength of LPFG is designed to match the peak of SRS gain spectrum. By inserting the LPFG before the output coupling FBG (OC-FBG) of the oscillator, an efficient mitigation of SRS is observed. LPFGs represent a highly cost-effective fiber structure with potential for SRS suppession in high power fiber laser systems.

We reported a compact, stable 12-picosecond Innoslab amplifier. A mode-locked seed laser with an initial power of 4.5W was amplified using a discrete beam path (DBP) configuration. The 1064nm Nd:YAG slab amplifier showed the high average output power of 165W at 1MHz of pulse repetition rate. The amplifier exhibited 16.6% of optical conversion efficiency. The long-term power stability of the laser system was calculated for one hour and the fluctuation was found to be 0.27%.

In this paper, a mathematic model is established for the end-pumped continuous-wave cesium vapor laser. The threedimensional calculation of amplified spontaneous emission (ASE) is presented. The ASE flux is calculated from every point through all possible paths inside the medium. We systemically investigate the influences of the cell radius, cell length, and cell wall temperature on ASE. The results show that the ASE effect can be decreased by adjusting these key factors. To the best of our knowledge, there have not been any reports on the ASE estimation in an end-pumped DPAL so far.

N51-type Nd-doped phosphate laser glass is recently developed at Shanghai Institute of Optics and Fine Mechanics, China, especially for high-power laser applications. One multiphysics model is utilized to simulate the thermal recovery process of a single large-sized N51 amplifier, 810×460×40 mm³ slab with 12 mm thick edge cladding. The change of the average temperature with time, as well as the temperature at five points located at the center, long and short edge side, corner of the laser slab, and center of the edge cladding, are numerically simulated and discussed. On the thermal recovery, the slab equilibration time and the self-equilibration time are determined by the average temperature and the maximum temperature difference with a function of recovery time, respectively. For the whole slab, the temperature distribution, temperature gradient distribution, and thermal stress distribution during the thermal recovery process after a single but strong pumping are also numerically simulated by the transient-analysis method. Based on these numerical data of the N51 laser slab, it is suggested that N51 would be applied in high power laser systems with a better thermal recovery performance, as well as a higher stimulated emission cross section.

Laser weapon is a complex system, which consists of laser, optical system, ATP (Acuisition Tracking Pointing)system, electronic control system and so on. It needs the close cooperation of structure, optics, electronics and other disciplines. Laser weapon has developed rapidly in recent years, and developed countries have increased investment in experiments. Laser weapon has the advantages of high cost-effectiveness ratio and light speed attack. It has been applied in vehicle, shipboard and airborne, and may develop into space application in the future. In recent years, drones play an increasingly important role in the battlefield. Laser weapon is a powerful weapon to deal with drones. Laser weapons can be classified into chemical lasers, solid-state lasers, free electron lasers and so on. Solid state laser will be an important direction of laser development in the future.

In this paper, we used a femtosecond laser direct writing system to fabricate all-fiber structure Fabry-Perot (FP) cavities based on fiber Bragg gratings (FBGs) on single-mode fibers, which was used as a scale for weak reflectivity measurement of output-coupling FBGs (OC-FBGs). By this method, the intensity of the Bragg resonance reflectivity peak of OC-FBG can be measured to be as low as ~1%. Compared with the traditional method based on the transmission spectrum, this method is much higher measurement accuracy.

In this paper, we design and fabricate a series of single-mode scale gratings based Fabry Perot (FP) by using excimer laser and chirped phase mask, then use it to measure the reflectivity of weak reflection gratings on large-mode-area doubleclad (LMA-DC) fibers. Experimental results show that the Bragg resonance reflectivity of the LMA-DC weak reflection grating is between 1.19% and 1.49%. The method of measuring weak reflection grating reflectivity based on scale grating is convenient, efficient, and the accuracy is greatly improved.

Laser induced damage in the final optics system is one of the bottleneck problems in the high-power laser system. For almost all the eight beams of final optics assembly (FOA), there are usually damages in the middle areas of the focusing lens in SG-II laser facility. Through detailed analysis, we find a correlation between the damage in the focusing lens and defect in the continuous phase plate (CPP). The main mechanism for downstream damage is regarded as the defect induced light intensification. The phase distribution of the CPP is characterized by coherent diffraction imaging method. Through simulation, we can clearly see a much stronger light intensification in the middle of the beam caused by the real CPP than the theoretical designed CPP. Compared with the designed CPP, there are defects on the CPP causing the downstream intensification. Meanwhile, there are unexpected periodic modulation on the surface of CPP. We assume the central defect is a kind of laser induced defect because the defects caused by the optical processing are randomly distributed. Through ray tracing analysis, we find a ghost image near the center of the CPP position. So the CPP is slightly damaged or modified in the middle area of the ghost image ray, thus forming a defect with strong modulation. A stray light management is proposed base on ground glass to mitigate the ghost image problem. The periodic modulation is possibly formed by the manufacturing process of CPP. Small-period modulation can cause greater downstream modulation. It should be controlled with power spectral density specification in the manufacturing process. Once the laser induced defect problem is solved, the laser induced damage in the middle of focusing lens is greatly mitigated.

A Nd:LuAG disk laser with V-shape stable resonator and active-mirror configuration, end-pumped by 808 nm laser diode array, is demonstrated. By using a theoretical model, performances and optimization of the disk laser is investigated theoretically and experimentally. A maximum output energy of 4.5 J per pulse operating at 10 Hz repetition rate is obtained for the laser with the optimum output coupler transmission of 15%, the corresponding optical-to-optical efficiency is 18.8%. It proves that Nd:LuAG ceramic active-mirror disk laser is a promising alternatives for high-energy lasers.

Large aperture frequency converters are important components of the high-power laser system. It is often composed of a cascaded KDP (Potassium Dihydrogen Phosphate) crystal and dKDP (potassium deuterium phosphate) crystal system. The effect of the stress distribution of KDP crystal on the second harmonic generation (SHG) efficiency has been studied. It is found that the phase mismatch has a linear relationship with unidirectional stress. The result of the case study shows that the stress-induced phase mismatch in the SHG process is needed to be paid more attention to in engineering.

Aiming at the requirement of illumination uniformity and backscattering suppression in laser-driven inertial confinement fusion (ICF) facilities, we propose a polarization smoothing (PS) scheme based on stress-engineered optical element that can modulate linearly polarized light into a full Poincaré beam. The unique law of modulation of the polarization state by glass window under symmetrical loads is revealed by numerical simulations, the results indicate that the glass window exhibits a fast axis orientation that rotates with the polar angle and a phase retardance that increases with the radius under more than two symmetrical pressure loads. Further optical calculations show that when the pressure of the loads and the thickness of the glass are sufficient, the window can modulate the linearly polarized light into a full Poincarébeam.

Optical properties of a Li₂B₄O₇ (LB4) crystal are determined in the spectral range 0.2-1.6 THz. Dispersion of the refractive index components for o- and e-wave are approximated in the form of Sellmeier equations. They are subsequently used to determine the possible interaction types and to calculate the phase-matching angles to get THz waves by difference frequency generation. The damage threshold is determined as well as the coherence length for all possible types of three wave interactions under the pump by fs Ti: Sapphire laser pulses at 950 nm. The efficiency of the processes is estimated. Using trains of hundreds of pulses at 950 nm it was found to be 1.32 times of that for β-BBO crystal laser pump.

The nondestructive and economical removal of sol-gel SiO₂ coating is significant for the recovery and reuse of fused silica optical elements. Compared with conventional wet cleaning process, ion beam etching as a dry cleaning process has atomic-scale removal capacity which is highly stable, non-contact and environment-friendly. In this research, a series of ion beam etching experiments is conducted to investigate the removal efficiency of antireflection sol-gel SiO₂ coating and substrate material. The etched surface roughness and optical performance are also studied. The best removal parameters during ion beam etching are determined based on the maximum removal efficiency ratio between antireflection sol-gel SiO₂ coating and substrate material. Moreover, the surface roughness and shape of fused silica are both improved during ion beam etching process. The optical transmission of etched surface is reduced to the substrate level and the surface chemical structure remains the same. The results can be a reference for using ion beam etching process technology to clean antireflection sol-gel SiO₂ coating of fused silica optics in inertial confinement fusion facility.

Cobalt-based superalloys have been widely used in manufacturing high-temperature parts of gas turbine missiles, such as combustion chambers, exhaust nozzles, and heat exchangers in the nuclear energy industry. In order to meet the requirements for rapid manufacturing of these large-scale and high-performance components, the laser melting deposition (LMD) technology has attracted great attention in recent years. At present, the printability evaluation of Cobalt-based superalloys powder needs in-depth study. In this study, a cobalt-based superalloy (GH5188) has been additively manufacturing by using LMD for the first time. The self-designed gas atomization equipment is used to prepare GH5188 alloy powder, LMD technology is used to prepare as-deposited samples, the key process parameters and the resulted microstructure and mechanical properties are investigated. The results show that as the energy density increases, the pores and unfused defects of the as-deposited GH5188 sample decrease. The microstructure of the GH5188 sample is composed of columnar dendrites grown epitaxially, and carbides are precipitated in the grain boundaries and inside the crystals. As the energy density increases, the columnar crystals of the GH5188 sample are obviously thicker, and the hardness and elongation of the sample increase significantly. When the energy density is 70J/mm, the tensile strength of the sample can reach 806.3MPa; when the energy density is increased to 80J/m, the elongation of the sample is 33.01%;

With the wide application of spaceborne lidar, 2 μm laser with high repetition rate and high energy has become an important candidate for coherent detection lidar. Conductively cooling is recognized as the critical technology for high energy, 2 μm lasers. The structure and thermal design of a totally conductively cooled, diode side-pumped, 2 μm laser amplifier is introduced in the paper. The amplifier consists of a 20-mm-long Tm: Ho: YLF crystal pumped by 2-banks of 3-radially arranged diode lasers (LD). Through the research and analysis of the structure and thermal coupling of the amplifier head, the conductively cooling scheme satisfying the need of the application in the space environment is obtained. The peak power consumption of LD is 200 W and the average heat consumption is 23.76 W at 10 Hz. When the coolant temperature is 17°C, the stable temperature of the crystal center is about 30°C, which achieves the result of 2.6 times of laser energy amplification. The experimental data matches the result very well.

Deformable mirrors in adaptive system for high power lasers should have high damage threshold and thermally stabilized surface. The cooling is required for average beam power above 100W. In this paper, the problem of the thermo-stabilizing of the deformable mirrors is studied. Bimorph deformable mirrors (BDM) and stack actuator deformable mirrors (SADM) are considered. For BDMs the active and passive cooling designs have been implemented. In active design, the waffletype cooling system for circulation of the cooling liquid was made inside of the thin substrate. In passive design, the periphery surface is thermally contacted with the condenser which temperature is constant. Such BDMs not damaged at CW power density 20kW/cm² when the beam fills full surface of the mirror and can be used in powerful solid state ceramic YAG lasers. SADM is most suitable to correct for small-scale and high-speed aberrations. We developed SADM where reflecting substrate is cooled through the actuator bodies. Individual actuators are housed in metal holders and can be replaced if they fail due to electrical breakdown. SADM has the diameter 120 mm and included 121 actuators. The deformation stroke of the actuator was 7μ. The first resonant frequency was 18.5 kHz, which allowed operating in adaptive system in kHz range.

In order to solve the problem of small deformation monitoring of tower cranes that cannot be achieved by traditional monitoring methods, the study of small deformation monitoring technology based on LiDAR data to establish a threedimensional visualization model has been carried out. Use a three-dimensional laser scanner to obtain the point cloud data of the tower crane. Based on the RANSANC algorithm and the optimized ICP algorithm, the point cloud data is processed to establish a three-dimensional visualization model, and the amount of tilt of the tower crane during the work process is compared through the comparison of the results of the two scans. Therefore, it is concluded that this method has greater advantages than traditional deformation monitoring methods. It realizes the deformation monitoring of small feature points and can calculate the deformation results faster and more accurately, which reflects the intuitiveness and real-time of 3D laser scanning. It is possible to eliminate potential safety hazards as much as possible. It will provide a favorable basis for future research on subtle deformation characteristics in buildings and other fields

In the amplifier of the large-aperture laser facility, the laser slab will have a depolarization effect in part areas due to the mounting stress and thermal stress. The depolarization effect will degrade the polarization state of the laser so that it cannot meet the design requirements, thereby affecting the efficiency of the whole facility. At the same time, depolarization will also cause low isolation in the facility and cause unpredictable damage to the optics. Aiming at the problem of depolarization, this article proposes a method to adjust the stress distribution of the laser slab by mounting load, and then adjust the polarization state of the slab, so that the stress distribution of the glass is uniform, and the position of the glass depolarization is controlled as far from the four corners as possible and minimize the influence of depolarization effect on the laser.

High-power laser systems have high requirements on the size, shape, and uniformity of the focal spot. Both continuous phase plate (CPP) and lens array (LA) can be used for beam shaping and smoothing. However, their ability is limited and there are few studies on the cooperation of CPP and LA. In this paper, the joint design of the CPP and LA was proposed, we theoretically analyzed its principle and studied the method to achieve better shaping and smoothing performance. Then, the far-field focal spot properties of three beam smoothing methods of the LA, the CPP, the CPP combined with the LA were obtained and compared through numerical simulation. The result shows that the LA is mainly contribution to shaping and the CPP mainly reduces the high-contrast intensity modulation to a certain extent. The joint design of the CPP and the LA greatly improves the uniformity of the far-field focal spot, which is valuable for expanding the application scope of the CPP and the LA.