This PDF file contains the front matter associated with SPIE Proceedings Volume 10339, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

We present an approach for green laser-light generation based on a fiber superluminescent pulse amplification system and frequency doubling to 552 nm with a periodically poled lithium niobate (PPLN) crystal. The SPA system used in the experiment is capable of yielding 6-nm-bandwidth, 10 ns pulsees. The 10-mm-long PPLN with 6.95 μm period and 0.5 mm thick generated high-power green light with single pulse energy up to 5.49 μJ when hte broadband input pulse coherence characteristics of the superluminescent pulse amplifier and the frequency doubling. This generated green light has proved to have low speckle noise and low photon degeneracy.

Three dimensional (3D) fast (< 0.5 hour) printing of micro-optical elements down to sub-wavelength resolution over 100 μm footprint areas using femtosecond (fs-)laser oscillator is presented. Using sub-1 nJ pulse energies, optical vortex generators made of polymerised grating segments with an azimuthally changing orientation have been fabricated in SZ2080 resist; width of polymerised rods was ~ 150 nm and period 0.6-1 μm. Detailed phase retardance analysis was carried out manually with Berek compensator (under a white light illumination) and using an equivalent principle by an automated Abrio implementation at 546 nm. Direct experimental measurements of retardance was required since the period of the grating was comparable (or larger) than the wavelength of visible light. By gold sputtering, transmissive optical vortex generators were turned into reflective ones with augmented retardance, Δn × h defined by the form birefringence, Δn, and the height h = 2d where d is the thickness of the polymerised structure. Retardance reached 315 nm as measured with Berek compensator at visible wavelengths. Birefringent phase delays of π (or λ/2 in wavelength) required for high purity vortex generators can be made based on the proposed approach. Optical vortex generators for telecom wavelengths with sub-wavelength patterns of azimuthally oriented gratings are amenable by direct laser polymerisation.

Optics manufactured by mechanical grinding and polishing inevitably will bring surface/subsurface damages and defects during the machining process. Laser polishing has been demonstrated as a technique capable of achieving ultra-smooth surface with no damage and low-defects, but by far optics polished by this technology are only sufficient for illumination applications. To achieve high quality optics, high precision laser ablation has been proved to be a promising technology for shape correction. With pulsed CO₂ laser, high precision laser ablation can be performed by direct evaporation of unwanted surface asperities. To acquire nanometer scale high precision ablation, an accurate control and meticulous adjustment of temperature should be needed. Herein, a mathematical model has been established to assist the understanding of the thermal mechanism of CO₂ laser ablation and subsequently a series of simulations have been extended to investigate the phase change of evaporation. The temperature of fused silica irradiated by CO₂ laser can be controlled via laser power and pulse duration. To achieve nanometer ablation depth, a gentle evaporation regime at low laser intensity is necessary. The results indicated that the ablation depth linearly depend on laser fluence and depth control levels of nanometer are obtainable with the control of laser fluence.

Two kinds of hafnia-silica polarizer coatings were prepared by electron beam evaporation, using hafnia-silica mixture (MPOL) and hafnia (POL) as the high refractive index materials, respectively. The spectral performance, surface and interfacial properties, as well as the laser induced damage performance were studied and compared. The M-POL coating shows better performance with broader polarizing bandwidth, lower surface roughness, better interfacial property, while maintaining high laser induced damage threshold.

Large high-power-laser facility is the basis for achieving inertial confinement fusion, one of whose missions is to make fusion energy usable in the near future. In the facility, fused silica optics plays an irreplaceable role to conduct extremely high-intensity laser to fusion capsule. But the surface defect of fused silica is a major obstacle limiting the output power of the large laser facility and likely resulting in the failure of ignition. To mitigate, or event to remove the surface defect, wet chemical etching has been developed as a practical way. However, how the surface defect evolves during wet chemical etching is still not clearly known so far. To address this problem, in this work, the three-dimensional model of surface defect is built and finite difference time domain (FDTD) method is developed to simulate the evolution of surface defect during etching. From the simulation, it is found that the surface defect will get smooth and result in the improvement of surface quality of fused silica after etching. Comparatively, surface defects (e.g. micro-crack, scratch, series of pinholes, etc.) of a typical fused silica at different etching time are experimentally measured. It can be seen that the simulation result agrees well with the result of experiment, indicating the FDTD method is valid for investigating the evolution of surface defect during etching. With the finding of FDTD simulation, one can optimize the treatment process of fused silica in practical etching or even to make the initial characterization of surface defect traceable.

It is an effective method to protect components from high power laser damage by using high reflective materials. The rare earth tantalates RETaO₄ with high dielectric constant suggests that they may have very high reflectivity, according to the relationship between dielectric constant and reflectivity. In this paper, the crystal structure, electronic structure and optical properties of RETaO₄ (RE=Y, La, Sm, Eu, Dy, Er) have been studied by first-principles calculation. The calculated lattice parameters are in good agreement with the previously reported values. With increasing the atomic number of RE (i.e., the number of 4f electrons), 4f electron shell moves from high energy region to low energy region, showing the tendency of moving from conduction band bottom to forbidden gap and then to valence band. The relationship between the electronic structures and optical properties is explored. The electron transitions between O 2p states, RE 4f states and Ta 5d states have a key effect on optical properties such as dielectric function, refractive index, absorption coefficient and reflectivity. For the series of RETaO4, the appearance of the 4f electronic states will obviously promote the improvement of reflectivity. When the 4f states appear at the middle of forbidden gap, the reflectivity reaches the maximum. The reflectivity of EuTaO₄ at 1064nm is up to 93.47%, indicating that it has potential applications in the anti-laser radiation area.

The damage resistance of 355nm laser can be improved for fluoride mirrors with an SiO₂ overcoat layer. Three kinds of samples are deposited with the overcoat layer of different thicknesses. Calculated with Stoney equation, the residual stress of the film can be altered to the compressive stress with the increase of the overcoat layer. Through the investigation of the damage pits, we find the damages are the thermal-mechanical coupled and induced by the nodules buried in the fluoride multilayers. The surface morphologies around the damage pits are analyzed from the two respects: Cracks and surface ablation. The two characters of the damage morphologies can be suppressed with the addition of the SiO₂ overcoat layer.

With the increasing in laser power, it is necessary to prepare protective coatings for components and devices under high power laser irradiation environment. Yttria-stabilized zirconia has high melting point, good stability and low thermal conductivity, and is often used as thermal barrier coating material. However, the study on its anti high power CW laser performance is rare. In this paper, the yttria-stabilized zirconia coating was deposited using atmospheric plasma spraying. The spectrophotometer, X-ray diffraction, scanning electron microscope and energy dispersive spectrometer were used to characterize the coating before and after high power CW laser irradiation. The temperature of substrate in back side was measured during irradiation. The results show that under the 2000 W/cm² laser power density continuously irradiated for 20 s, the back temperature is only 250 °C. Even continuously irradiated for 60 s under this power, no obvious damage appears on the coating. Only the phenomenon of micro melting in the irradiation center was observed under scanning electron microscope. The coating shows excellent anti-laser irradiation ability.

Many literatures have focused on the design, fabrication and intrinsic damage of multilayer dielectric gratings (MLDGs). However, contamination may be a key factor of the MLDGs lifetime. In this paper, we compare the laser damages of the clean and contaminated MLDGs, and damage threshold of clean MLDGs is 3.12J/cm² . We obtain the curve of the critical particle size at various laser fluences, above which the MLDGs will be damaged. Intrinsic LIDT of clean MLDGs is larger than that of contaminated ones, so the cleanness control is a crucial problem for the MLDGs. The scanning electron microscope (SEM) morphologies of intrinsic and contaminant induced damages are different. The intrinsic damage is cold ablation, while contaminant induced damage is thermal ablation.

Hot-images’ formation process from damage sites to locations after nonlinear mediums is analyzed under high flux theoretically and numerically. Analysis shows that peak intensities of hot images scarcely change with damage depth whereas there can be a variation of locations which is approximately the thickness of the nonlinear medium. Considering that hot images appear periodically on alternating mediums, a gradient direction matching method with high signal-to-noise ratio is proposed to prejudge hot images, which is calculated efficiently with FFT method. It calculates damage sites’ properties inversely with the extracted diffraction intensities from the detected ring’s center. Accuracies of the inversed diffraction length and damage size are experimentally studied with the single diffraction ring. As intensity is disturbed by random noise, accuracy of damage size has an error of about tens of microns. Images are usually full of random noise. Experimental result shows that this algorithm can accurately find the diffraction center under this circumstance. Rings are generally overlapped with each other, so the resolution is studied when two rings are overlapped with different percentages. Experimental result shows that the minimum spacing between two damage sites is 1.374 mm when diffraction length is 245 mm. A method using a fan-shaped template is put forward to improve the resolution of the overlapped diffraction rings when the diffraction intensities are disturbed seriously. Results show that this algorithm can prejudge hot images quickly prior to the initiation of a full-system shot.

An extra-laser cavity CO₂-TEA laser pulse clipper using gas breakdown techniques for high spatial resolution material processing and shallow material engraving and drilling processes is presented. Complete extinction of the nitrogen tail, that extends the pulse width, is obtained at pressures from 375 up to 1500 torr for nitrogen and argon gases. Excellent energy stability and pulse repeatability were further enhanced using high voltage assisted preionized plasma gas technique. Experimental data illustrates the direct correlation between laser pulse width and depth of engraving in aluminum and alumina materials.

We investigated the morphology and mechanism of laser-induced damage in the ablation cutting of thin glass sheets with picosecond laser. Two kinds of damage morphologies observed on the cross-section of the cut channel, are caused by high-density free-electrons and the temperature accumulation, respectively. Notches and micro-cracks can be observed on the top surface of the sample near the cut edge. The surface micro-cracks were related to high energy free-electrons and also the heat-affected zone. Heat-affected-zone and visible-cracks free conditions of glass cutting were achieved by controlling the repetition rate and spatial overlap of laser pulses.

Combining high power laser irradiation and emission spectra measurement system, the photoluminescence properties of KDP crystal under high power laser irradiation were studied. Photoluminescence measurement was performed using 532 nm and 355 nm laser excitation at relatively high laser fluence but still under the laser induced damage threshold. Four emission peaks, centered at 559 nm, 586 nm, 609 nm and 621 nm, were observed while irradiated by high power laser at 532 nm. Five emission peaks, centered at 358 nm, 365 nm, 377 nm, 385 nm and 390 nm were observed under high power laser irradiation at 355 nm. Based on the analysis of wave number transformation, these peaks were attributed to the Raman scattering.

The performance of deuterated potassium dihydrogen phosphate (DKDP) crystal directly affects beam quality, energy and conversion efficiency in the Inertial Confinement Fusion（ICF）facility, which is related with the initial saturation temperature of solution and the real-time supersaturation during the crystal growth. However, traditional method to measure the saturation temperature is neither efficient nor accurate enough. Besides, the supersaturation is often controlled by experience, which yields the higher error and leads to the instability during the crystal growth. In this paper, DKDP solution with 78% deuteration concentration is crystallized in different temperatures. We study the relation between solubility and temperature of DKDP and fit a theoretical curve with a parabola model. With the model, the measurement of saturation temperature is simplified and the control precision of the cooling rate is improved during the crystal growth, which is beneficial for optimizing the crystal growth process.

Large-aperture and long focal-length lens is widely used in high energy laser system. The method based on Talbot interferometry is a reliable method to measure the focal length of such elements. By employing divergent beam and two gratings of different periods, this method could realize full-aperture measurement, higher accuracy and better repeatability. However, it does not take into account the spherical aberration of the measured lens resulting in the moiré fringes bending, which will introduce measurement error. Furthermore, in long-focal measurement with divergent beam, this error is an important factor affecting the measurement accuracy. In this paper, we propose a new spherical aberration compensation method, which could significantly reduce the measurement error. Characterized by central-symmetric scanning window, the proposed method is based on the relationship between spherical aberration and the lens aperture. Angle data of moiré fringes in each scanning window is retrieved by Fourier analysis and statistically fitted to estimate a globally optimum value for spherical-aberration-free focal length calculation. Simulation and experiment have been carried out. Compared to the previous work, the proposed method is able to reduce the relative measurement error by 50%. The effect of scanning window size and shift step length on the results is also discussed.

Transient transmission and scattering changes was observed to study the dynamics during the laser-induced bulk damage in fused silica at the wavelength of 532 and 355 nm. Within the nanosecond high power laser irradiation, the transmittance decreased dramatically, indicating an intense absorption. With fluence increasing, the time required to form the intense absorption was shortened, and at similar fluence, this time interval at the wavelength of 355 nm is shorter than that at 532 nm. At times, the intense absorption did not cause the macroscopic damage because no variation in scattering was observed. While the macroscopic damage occurred, the scattering kept on increasing until the end of pulse.

Spectral beam combining (SBC) laser systems are rapidly advancing the output power scaling for high-average-power beam-combined fiber lasers with near-perfect beam quality. Grating as the dispersive element requires high diffraction efficiency (DE) and broad bandwidth (BW) for improving the combined output power scaling. A broad BW high DE polarization-independent reflective multilayer dielectric (MLD) grating is designed. The -1st order DE of the designed grating exceeds 99.84% at 1053nm central wavelength. The BW of the grating with the -1st order DE higher than 99% is up to 99 nm for non-polarized incident light. This MLD grating can be used as a reliable combiner in the SBC system.

A fatigue effect is often observed under multiple laser irradiations, overall in UV. This decrease of LIDT, is a critical parameter for laser sources with high repetition rates and with a need of long-term life, as in spatial applications at 355nm. A challenge is also to replace excimer lasers by solid laser sources, this challenge requires to improve drastically the lifetime of optical materials at 266nm. Main applications of these sources are devoted to material surface nanostructuration, spectroscopy and medical surgeries. In this work we focus on the understanding of the laser matter interaction at 266nm in silica in order to predict the lifetime of components and study parameters links to these lifetimes to give keys of improvement for material suppliers. In order to study the mechanism involved in the case of multiple irradiations, an interesting approach is to involve the evolution of fluorescence, in order to observe the first stages of material changes just before breakdown. We will show that it is sometime possible to estimate the lifetime of component only with the fluorescence measurement, saving time and materials. Moreover, the data from the diagnostics give relevant informations to highlight “defects” induced by multiple laser irradiations.

We measured the absorption of type I doubler KDP crystal at different laser wavelengths (1064, 532 and 355 nm) by using laser induced deflection (LID) technique. We also performed the absorption measurements in the cases where beam polarization was parallel to the principal plane (Pd//Pp) and perpendicular to it (Pd⊥Pp). To account for the experiment results, a model based on crystal dichroism was developed to calculate the absorption coefficients for O ray (α_o) and E ray (α_e) at different laser wavelengths. It is found that the dichroism is manifested especially clearly at 1064nm, but not clearly at 355nm/532nm. It implies that the absorption at 1064nm is mainly due to lattice absorption, whereas defects absorption is responsible for the absorption at 355nm/532nm.

Surface absorption defect has significant effects on the laser damage in the high power laser systems. Photothermal absorption measurement system based on the laser induced surface thermal lensing (STL) effect has been widely used in the research on the correlation between laser damage susceptibility and properties of weak absorption defects for small optical specimens. In this paper, we present the progress in the development of an automated measurement system for large aperture optics with a size around 400mm. The wavelength at 1064nm is used as the pump laser to investigate the absorption properties for the inspected site. The system which shows a measurement sensitivity of absorbance down to 0.1 ppm and measurement repeatability of 10% requires little special skills from the operators and is therefore more reliable and reproducible. The specific applications of the system include weak absorption measurement, local absorption defects detection as well as laser-coating-interaction dynamics monitoring. The high sensitive automated system proposed in this work is an effective diagnostic tool for the examination of large aperture optics with desired optical properties.

Ytterbium-doped fiber laser (YDFL) and Thulium doped fiber laser (TDFL) have been two kinds of the most widely studied fiber laser in recent years. Although both silica-based Ytterbium-doped fiber and Thulium doped fiber have wide emission spectrum band (more than 200 nm and 400 nm, respectively), the operation spectrum region of previously demonstrated high power YDFL and TDFL fall into 1060-1100 nm and 1900-2050nm. Power scaling of YDFL and TDFL operates at short-wavelength or long-wavelength band, especially for extreme wavelength operation, although is highly required in a large variety of application fields, is quite challenging due to small net gain and strong amplified spontaneous emission (ASE). In this paper, we will present study on extreme wavelength operation of high power YDFL and TDFL in our group. Comprehensive mathematical models are built to investigate the feasibility of high power operation and propose effective technical methods to achieve high power operation. We have achieved (1) Diodepumped 1150nm long wavelength YDFL with 120-watt level output power (2) Diode-pumped 1178nm long wavelength YDFL operates at high temperature with 30-watt level output power (3) Random laser pumped 2153nm long wavelength TDFL with 20-watt level output power (4) Diode-pumped 1018nm short wavelength YDFL with a record 2 kilowatt output power is achieved by using home-made fiber combiner.

A measurement system for diffraction efficiency of convex gratings is designed. The measurement system mainly includes four components as a light source, a front system, a dispersing system that contains a convex grating, and a detector. Based on the definition and measuring principle of diffraction efficiency, the optical scheme of the measurement system is analyzed and the design result is given. Then, in order to validate the feasibility of the designed system, the measurement system is set up and the diffraction efficiency of a convex grating with the aperture of 35 mm, the curvature-radius of 72mm, the blazed angle of 6.4°, the grating period of 2.5μm and the working waveband of 400nm-900nm is tested. Based on GUM (Guide to the Expression of Uncertainty in Measurement), the uncertainties in the measuring results are evaluated. The measured diffraction efficiency data are compared to the theoretical ones, which are calculated based on the grating groove parameters got by an atomic force microscope and Rigorous Couple Wave Analysis, and the reliability of the measurement system is illustrated. Finally, the measurement performance of the system is analyzed and tested. The results show that, the testing accuracy, the testing stability and the testing repeatability are 2.5%, 0.085% and 3.5% , respectively.

With the aim to fabricate high quality and boosting the optical performance of vanadium dioxide (VO₂) film, basing on effective medium theory, dual-target magnetron sputtering method is first introduced into VO₂-SiO₂ composite film on quartz by changing the flow ratio of Argon and oxygen. X-Ray diffraction measurement indicates the purity of the composite film. Atomic force microscopy measurement shows that the minimum grain size is about 45nm. Infrared (IR) switching characteristic is well demonstrated by a double-frequented He-Ne laser at the wavelength of 3mμ,compare to VO₂ film obtained at the same sputtering time, the result reveals that the composite film exhibit excellent IR switching property, furthermore, multi-wavelength tests and calculations show that all of the obtained composite films exhibit high integrate luminous transmittance of 50%, and the transmittance in semiconducting phase of one thin film is 65% and decreases to 24% in metallic phase at the wavelength of 2mμ , with the switching efficiency of 63%. High visible transmittance and excellent infrared switching characteristics make the film an appropriate candidate for laser protection as well as smart windows.

In this paper, the wavelet threshold denoising method was used and combined into the FBP algorithm to reconstruct the imaging. To overcome the drawbacks of the traditional wavelet threshold functions, an improved wavelet threshold function was proposed, and to improve the reconstruction effect of image, the shift-invariant method was coupled into the improved wavelet threshold function. To verify the feasibility of the improved wavelet threshold function combined with shift-invariant method, the simulation experiments of the standard brain phantom were performed by using the FBP algorithm based on different wavelet threshold functions at the software platform of MATLAB. In addition, the peak signal-to-noise ratio (PSNR) and mean-square-error (MSE) values of different methods were computed. Experimental results show that, compared with traditional wavelet threshold functions, the image reconstruction based on the FBP of the improved wavelet threshold function combined with shift-invariant method has better reconstruction effect. Among the SL, RL, and Hann filters for the FBP of the improved wavelet threshold function combined with shift-invariant method, the PSNR value based on RL filter was increased 38.7%, and the MSE value was increased 82%. Keywords: image reconstruction, filtered back-projection algorithm, wavelet threshold denoising.

In this study, to discriminate the glucose and the white sugar gradient in the food, a noninvasive optical detection system based on pulsed laser-induced photoacoustic technique was developed. Meanwhile, the Nd: YAG 532nm pumped OPO pulsed laser was used as the excitation light source to generate of the photoacoustic signals of the glucose and white sugar. The focused ultrasonic transducer with central detection frequency of 1MHz was used to capture the photoacoustic signals. In experiments, the real-time photoacoustic signals of the glucose and the white sugar aqueous solutions were gotten and compared with each other. In addition, to discriminate the difference of the characteristic photoacoustic signals between both of them, the difference spectrum and the first order derivative technique between the peak-to-peak photoacoustic signals of the water and that of the glucose and white sugar were employed. The difference characteristic photoacoustic wavelengths between the glucose and the white sugar were found based on the established photoacoustic detection system. This study provides the potential possibility for the discrimination of the glucose and the white sugar by using the photoacoustic detection method.

Remote sensing satellite camera imaging simulation technology is broadly used to evaluate the satellite imaging quality and to test the data application system. But the simulation precision is hard to examine. In this paper, we propose an experimental simulation verification method, which is based on the test parameter variation comparison. According to the simulation model based on ray-tracing, the experiment is to verify the model precision by changing the types of devices, which are corresponding the parameters of the model. The experimental results show that the similarity between the imaging model based on ray tracing and the experimental image is 91.4%, which can simulate the remote sensing satellite imaging system very well.

Laser processes of crystalline silicon solar cells become increasingly attractive, because they are fast, accurate and contact-free. Nanosecond and picosecond laser ablations with wavelength of 532nm were performed on the anti-reflection layers deposited on silicon. The laser ablated grooves of AR coatings on monocrystalline and polycrystalline silicon were both characterized to verify the influence on the underlying silicon. And the threshold fluences were specified by contrasting with the corresponding performances under certain laser pulse duration. More importantly, the groove edges were analyzed to further expose the laser ablation mechanism under different laser pulse durations.

In this paper, a new type of calibration mechanism based on worm drive is presented for a space telescope. This calibration mechanism based on worm drive has the advantages of compact size and self-lock. The mechanism mainly consists of thirty-six LEDs as the light source for flat calibration, a diffuse plate, a step motor, a worm gear reducer and a potentiometer. As the main part of the diffuse plate, a PTFE tablet is mounted in an aluminum alloy frame. The frame is fixed on the shaft of the worm gear, which is driven by the step motor through the worm. The shaft of the potentiometer is connected to that of the worm gear to measure the rotation angle of the diffuse plate through a flexible coupler. Firstly, the calibration mechanism is designed, which includes the LEDs assembly design, the worm gear reducer design and the diffuse plate assembly design. The counterweight blocks and two end stops are also designed for the diffuse plate assembly. Then a modal analysis with finite element method for the diffuse plate assembly is completed.

We report a close connection between the fluctuation characteristics of the electrical derivative (ED) initial peaks and the 1/f noise intensities of different samples we found during the investigation of the 1/f noise origins of InGaAs quantum well high-power semiconductor laser diodes (LDs). We conduct contrast measurements on over fifty samples, where the current 1/f noise is measured under different bias currents, expressed by power spectrum density (PSD) and the EDs are computed from the current-voltage (I-V) measurement results. Then the influence of 1/f noise on the ED initial peaks is presented by comparing these parameters of different samples. The results show a clear pattern between the noise intensity and the ED initial peak fluctuation, and distinct differences between functional and aged LD devices, showing that ED initial peak can also be a non-destructive testing method for high power LD cavity damage and surface defects.

355nm UV lidars are of high spectral resolution and are demanded in space-borne applications. As a result of the vulnerability of the coatings in the laser systems and coatings irradiated by 355nm UV laser are more prone to be damaged than visible or infrared lasers. Thus, the study of the processing on substrate surface will contribute to the improvement of the performance of optical coatings. The dual ion beam sputtering can provide compact and stable layers for space applications. Thus, Al₂O₃/SiO₂ high reflection(HR) and anti-reflection(AR) coatings deposited on acid etched substrate were prepared by dual ion beam sputtering. Damage characteristics on the surface were analyzed after 355nm laser irradiation on the coatings. The damage morphology measured by focused ion beam-field emission scanning electron microscopy (FIB-FESEM) and depth measurement of damage pits hint that the damage of HR coatings occurs in the coating layers rather than the substrate. The HR and AR coatings deposited on acid etched substrate are of larger changes on laser-induced damage thresholds(LIDT) than these on the non-etched substrate. The damage mechanisms of coatings are attributed to thermal absorption and the damage area is a molten pool surrounded by mechanical ejection. The etched area with nicks caused the damage on the HR coatings deposited on etched substrate. And due to the elimination of defects on the subsurface of the AR coatings by etching method, the LIDT of AR coatings was improved.

Potassium dihydrogen phosphate (KDP) crystals are essential components used in the high power laser applications. Its properties will affect the output power and quality of laser beam directly. To improve the laser-induced damage threshold (LIDT) of KDP crystal, this paper investigated the influence of ion beam figuring(IBF) technology on the laser damage properties of KDP crystal machined by single point diamond turning(SPDT). Firstly, the surface quality and photo-thermal absorption performance of samples were measured after turning and ion beam figuring. Then, the LIDT of crystal of different processing conditions were measured by R-on-1 test method. Finally, the mechanisms that ion beam figuring could improve the LIDT were analyzed and discussed.The experiment results show that ion beam figuring can reduce surface roughness,improve the surface quality as well as lower the absorption of KDP crystal elements, which contribute to increase the laser damage resistance of KDP crystals obviously.

For its compact size and light weight, space telescope with deployable support structure for its secondary mirror is very suitable as an optical payload for a nanosatellite or a cubesat. Firstly the realization of a prototype deployable space telescope based on tape springs is introduced in this paper. The deployable telescope is composed of primary mirror assembly, secondary mirror assembly, 6 foldable tape springs to support the secondary mirror assembly, deployable baffle, aft optic components, and a set of lock-released devices based on shape memory alloy, etc. Then the deployment errors of the secondary mirror are measured with three-coordinate measuring machine to examine the alignment accuracy between the primary mirror and the deployed secondary mirror. Finally modal identification is completed for the telescope in deployment state to investigate its dynamic behavior with impact hammer testing. The results of the experimental modal identification agree with those from finite element analysis well.

Signal to noise ratio and depth accuracy are modeled for the pseudo-random ranging system with two random processes. The theoretical results, developed herein, capture the effects of code length and signal energy fluctuation are shown to agree with Monte Carlo simulation measurements. First, the SNR is developed as a function of the code length. Using Geiger-mode avalanche photodiodes (GMAPDs), longer code length is proven to reduce the noise effect and improve SNR. Second, the Cramer–Rao lower bound on range accuracy is derived to justify that longer code length can bring better range accuracy. Combined with the SNR model and CRLB model, it is manifested that the range accuracy can be improved by increasing the code length to reduce the noise-induced error. Third, the Cramer–Rao lower bound on range accuracy is shown to converge to the previously published theories and introduce the Gauss range walk model to range accuracy. Experimental tests also converge to the presented boundary model in this paper. It has been proven that depth error caused by the fluctuation of the number of detected photon counts in the laser echo pulse leads to the depth drift of Time Point Spread Function (TPSF). Finally, numerical fitting function is used to determine the relationship between the depth error and the photon counting ratio. Depth error due to different echo energy is calibrated so that the corrected depth accuracy is improved to 1cm.

The occurrence of the damage among the silica glass being laser-irradiation is closed related with the hydrogen. The laser of 248nm lead to the structure collapsing to made the silica glass crystallized. With the crystallized and non- crystallized parts, the 1H MAS NMR result shows that the concentration of the hydrogen are different of the damaged and non-damaged silica glass. Which is the evidence for the damage-delaying by the hydrogen.

To research the formation and variation principle of the weld seam and molten pool for aluminum alloy high power fiber laser welding, the welding experiments for 5052 aluminum alloy were carried out. The influences of laser power, scanning velocity and protection gas on the welding process were systematically researched. The results show that with the increase of power and scanning velocity, the depth to width ratio first increases and then decreases. The ratio reaches the maximum value at 2.6 KW and 30 mm/s, respectively. When the power located at 2.6 KW to 2.8 KW or the velocity located at 25 mm/s to 30 mm/s, stable deep penetration welding can be obtained. The weld seam shows relative flat appearance and the molten pool presents typical “T shape” topography. Moreover, the protection gas also influences the appearance of the weld seam. Using the independently designed fixture, the quality of the weld seam can be well improved.

We present z-propagation single-mode Ti: Er: Tm: LiNbO₃ strip waveguides on X-Cut congruent LiNbO₃ substrate. The waveguide has been fabricated by a technological process, starting with the preparation of the Er³⁺/Tm³⁺codoped LiNbO₃plate, followed by the fabrication of 8-μm-wide Ti-diffused strip waveguide. The results of surface refractive indices by employing prism coupling technique shows Er³⁺/Tm³⁺codoped have no effects on the substrate index, and the surface composition was evaluated from the measured indices with the help of Sellmeier equation. We demonstrated the amplified simultaneous emission (ASE) spectra from the waveguide pumped at 980nm and 795nm without optical damage observed. The results shows that the co-doping combines the laser property of both ions, and the emission band around 1.5μm is about 150 nm, as a result, opening up a series of possibilities for stable, broadband amplifier devices by employing pump sources under 980nm and 795nm laser diodes.

Multiple-slit diffraction properties of high-polarization-order cylindrical vector (HCV) beams were studied in detail. Flowerlike intensity distributions are obtained after HCV beams passing through a linear polarizer. The intensity distributions of single-slit, double-slit, triple-slit and four-slit diffraction of high-order radially polarized (HRP) beams and high-order azimuthally polarized (HAP) beams are obtained, and analyzed with different slit spacings. It was indicated that diffraction fringes of HCV beams were not continuous. Faultage appeared, and the faultage number was 2P+1, which was only related to the polarization order number P, but independent of slit number N. It was found that the obvious and clear diffraction phenomenon would be obtained in the conditions 2ω≈ (N+1)D, N≥2 in which ω₀ is the beam waist radius and D is the slit spacing. This study can be used to detect and analyze higher-order vector beams. Besides, it helps to design special diffractive optical elements.

To study the thermal damage process of optical film induced by continuous wave lasers, a model with contaminants on the surface of optical film is established. Based on the temperature field theory and heat conduction theory, we apply finite element method (FEM) to calculate the thermal damage process of the optical films. The results show that contaminants on the surface play an important role in the damage process of optical film. Finally, we compare the calculated results with our experimental data, and the calculated thermal damage process of film is in agreement with our experimental record.

In order to achieve aspheric high efficiency and low damage fabrication，and find the balance between damage and efficiency during the lapping, a SSD model based on fracture mechanics is given. Based on three body wear theory， a material removal model has been given. Based on the above two models, effective removal rate of damage model has been presented. The relationship between effective removal rate of damage and various factors has been analyzed by simulation. The effective removal rate of damage of diamond powder is smaller than the silicon carbide, so it is easy to achieve high efficiency and low damage fabrication. The presentation of effective removal rate of damage provide an evaluation criterion for aspheric high efficiency and low damage fabrication.

In high-energy laser facility, the residual nano-particles that are remained in mechanical system or produced by the interaction of kinetic-pairs are inevitable. The generation and the propagation of particulate pollutants will seriously reduce the performance of the laser systems. Therefore, the research about the adsorption behavior of particle contaminants on fused silica is very important to maintain the optical components’ surface clean, reduce induced damage, and finally prolong the life of the optical components. In this paper, the adsorption behavior between aluminum nano-particles and fused silica was simulated by molecular dynamics method. The effect of the surface roughness of fused silica on the state of adsorption and the state before adsorption has been studied. Then an experiment system based on an atomic force microscope was established to measure the adsorption force and further to verify the simulated results. Finally, the adsorption mechanism between metallic nano-particles and fused silica was revealed. The results show that surface roughness and the size of the particles are two of the main factors to influence the adsorption force. The rough fused silica surface can be “particle-phobic” due to the decreased contact area, which is beneficial to keep the fused silica surface clean.

We report on multiple solitons generation in an all-normal-dispersion (ANDi) passively mode-locked Yb-doped fiber ring laser with a cascaded long-period fiber grating as a spectral filter. Several different characteristic pulse modes have been experimental observed from the same ring laser by adjusting the polarization controllers, including uniform multiple solitons and nonuniform pulse-trains. In the uniform multiple solitons, the separation between the adjacent solitons is independent of the number of solitons, which is fixed at 33.6 ns. In the nonuniform pulse-train, multiple solitons up to 8 have been observed coexisting in the cavity, and the time distribution of the solitons is fixed at 21.1 ns, 12.5 ns and 8.6 ns, respectively. The observed results of multiple solitons output will not only have the potential applications in molecular detection, remote sensing and laser communication, but also be helpful to understand the mechanism of multi-solitons generation in the fiber laser system.

To further improve the laser-induced damage threshold of fused silica elements after Hydrogen Fluoride (HF) acid dynamic acid etching, the effect of the nanoparticle SiO₂ jet polishing on the surface quality and laser damage properties of fused silica was studied. On the fused silica surface after HF acid dynamic etching, different depths were polished with nanoparticle SiO₂ jet, and their surface roughness were measured by In-situ detection. The photothermal absorption, laser damage threshold and surface contamination element concentration at different depths were measured. The experimental results show that the RMS value of the surface roughness of the surface is reduced from 1.440nm to 0.507nm, and surface contamination elements are removed. The laser damage threshold is improved by 10%. The results show that nanoparticle SiO₂ jet polishing can remove surface damage and contamination after HF acid dynamic etching on the basis of elastic processing. Therefore, laser damage threshold can be improved.

We present the design and fabrication approach of a rugate narrow band minus filter. A method for the fabrication of graded-index coatings by rapidly alternating deposition of low (SiO₂) and high (Al₂O₃) refractive index materials is introduced, and this technology was used to fabricate a rugate structure. This paper mainly discusses about rugate narrow band minus filter design and fabrication approach. The experimental results show the measured transmittance spectra are in good agreement with the designed value. The laser-induced damage threshold (LIDT) of the narrow band rugate minus filter is measured.

Optical components are often damaged by hot images in high power laser system, especially for the final optics assembly. There are several nonlinear optical elements and a focusing lens. So both the hot images in free space propagation and in the focusing system are theoretically and numerically studied. We find that the focusing lens moves the hot images towards the lens. Through Fresnel number, the connection of hot image position in free space propagation and in the focusing system is discussed. What’s more, the nonlinear effect of the focusing lens is also considered for the hot images formation because the lens is sometimes very thick. At last, the influence of the size and modulation depth of scatter on the hot images position and intensity are also given. The hot images analysis is essential for the final optics assembly design, which can shed some light on avoiding the optical damage.