SiC crystals are used for a high refractive index material, as the frequency-selected device of Brewster plate. A stable single- longitudinal- mode green laser with an output power of 120 mW is achieved. Both the theoretical analysis and experimental results show that, compared with the common frequency-selected device using K9 glass as Brewster plate, the new frequency-selected device using the high refractive crystal of SiC as Brewster plate makes it easier to adjust the entire optical system. Moreover, the device works more stably, be much easier to achieve commercialization.

Based on the Y-shaped cavity orthogonal polarized dual-frequency helium-neon laser, the influences of pump current, operating point as well as the loss of resonator on the locking-threshold frequency difference are analyzed according to Lamb′s semi-classical theory. In order to measure the minimum frequency difference of the Y-shaped cavity orthogonal polarized dual-frequency helium-neon laser, an experimental system is set. Various factors, especially pump current and operating point, are studied in the experiment for the first time. The results show that either the pump current increasing or operating point approaching the gain curve center can cause the minimum frequency difference to decrease. When the pump current value is greater than 2.2 mA with its working state at the optimal operating point, the locking-threshold frequency difference can be less than several MHz.

Optical resonator with high quality factor Q values can be used as the core component of the resonator optic gyros, the miniaturization and integration of which can be achieved. These advantages develope the basis of current research in resonator gyroscope. In order to realize the integrated optical gyro with high sensitivity, on the basis of the production target of high Q value, large diameter cavity of integrated optical cavity fieldwiththedisc cavity core sensitive element is proposed for the application of resonant optical gyro. The correspondence between the Q value of disc cavity, DQ product (product of the diameter ofresonant cavity D and Q value), the sensitivity of optical resonator and the diameter of disc cavity can be analyzed by the theoretical calculation. In the experiment the disc cavity areprepared by the semiconductor process. Control the mask to achieve various diamond from 400 μm to 10 mm. The output transmission of disc cavity is collected through tapered fiber coupling, the result is that the Q factor is proportional to the change of the diameter of the disc cavity. When D=10 mm, the quality factor of the disc cavity is Q=1.2 × 106, which can achieve the optimal gyro sensitivity of about 0.02°/s, and meet the requirements of business level application, which lays the foundation for research on a novel resonant optical chip level, integration of the micro resonator gyroscope.

The fundamental wavelengths are oscillated at 1064 nm and 1342 nm in a diode array pumped Nd∶YVO4 laser. Continuous wave (CW) sum frequency generation (SFG) of 593.5 nm is achieved by placing the nonlinear optical crystal LiB3O5 (LBO) cut as type-I phase matched in the cavity. Noise characteristics of CW intracavity SFG laser is measured and analyzed in different experiment conditions. The multi-longitudinal modes structure and transverse modes pattern of SFG laser is observed in high and low noise operation by Fabry-Perot (F-P) scanning interferometer and beam profile instrument, respectively. The results show that noise characteristics of SFG laser is closely related to the multi-longitudinal modes structure which is associated with the pumping power and the resonator cavity perturbation. Compared with unstable multi-longitudinal modes structure, the output laser with stable multi-longitudinal modes structure is lower noise operating. In addition, higher-order transverse modes pattern can also cause the increase of laser noise.

Taking advantage of multi-angles light paths in end-pumped slab amplifier, a measurement system of characteristic factors of end-pumped slab amplifier is established, which can accurately detect the extracted power, wavefront distortion and depolarization at the same time. This system contains a kilo watt level and narrow linewidth seed source, highly accurate detectors of thermal induced wavefront distortions and depolarization. When the seed source is 2.7 kW and the pump current is 90 A, the extracted power from the slab amplifier is about 2.9 kW, the wavefront distortions is less than 1 μm (aperture of 27 mm), and the depolarization is about 5.1%. Compared with the factors under the non- extraction, the differences between them are distinct, which proves that the detecting system is essential to accurately acquire the qualities of slab amplifiers.

In high power excimer laser system, in order to achieve short pulse amplification and fine spot uniformity, angular multiplexing technique is adopted. So there are many laser beams and optical transmission links, which make the system complicated. In order to ensure the system working stably and efficiently, it needs to monitor and evaluate the status of all the links of system, which means online measurement of each amplification stage and multiple laser beams. Therefore, considering the character of the high power excimer laser system, a measure technique based on time-sequence method is proposed and principle experiments are carried on. Using this technique, online measurement of multiple beams using only one set of measuring elements can be achieved. The merit of this method is not only measurement efficiency can be promoted, but also the complication and cost is brought down, and the system errors caused by different elements are also avoided.

A nanosecond Er/Yb co-doped all-fiber dual-cavity laser with fiber-based passive Q-switch is reported. The laser oscillator is constructed in a linear dual-cavity, and can achieve the efficient, stable nanosecond operation based on the saturable absorber of the single- mode double- cladding Er/Yb co- doped fiber and the crossmodulation of the dual-cavity. The maximum output power is 2.2 W, and the minimum pulse duration is 173 ns with the central wavelength of 1570 nm. Meanwhile, sequential nanosecond pulses can be obtained at the repetition rate of 14~156 kHz.

A watt-level 100-nm tunable 2.8 μm-band mid-infrared fiber laser is demonstrated. By employing a blazing grating as the feedback, output power exceeding 1 W, tuning range of higher than 100 nm from heavi ly Er3+-doped ZBLAN double-clad fiber pumped by a laser-diode centered at 975 nm is obtained in continuous wave regime. Output power at 2.831 μm of the fiber laser is 1.02 W corresponding to the slope efficiency as high as 21.6%.

In diode laser array (DLA) grating-external cavity spectral beam combining (SBC) system, the total effects of lens aberration, fabrication error of grating and‘smile’effect may lead to the light crosstalk between light-emitting units of DLA. Based on the analysis of generating mechanism of light crosstalk, the main kinds of light crosstalk can be divided into two categories, including the stray light returning to the light-emitting unit itself and other units due to the feedback of external cavity, resulting in the self-oscillation and coupled oscillation. On the above basis, the diode laser rate equation involving light crosstalk has been put forward, and the combining efficiency of DLA emitters has been derived. Furthermore, the impacts of the self-oscillation and coupled oscillation on the combining efficiency have been analyzed. Results indicate that the two categories of light crosstalk involving both the stray light returning to the light-emitting unit itself and the stray light injected into other units decrease combining efficiency of light-emitting unit to different extents, and the impact of the latter is larger. In practical applications, some methods should be taken to control the light crosstalk.

The effects of induction heating local heat treatment and vacuum furnace overall heat treatment on the residual stress and tensile properties of laser deposition repair GH4169 superalloy are investigated. As compared with as-deposited samples, direct aged microstructure of laser deposition repair GH4169 superalloy changes little, and still presents the microstructural characteristic of columnar dendrites which grow epitaxially from the substrate. But Laves phase of interdendritic dissolves partly. The residual stress is reduced. The tensile strength is significantly improved. After local heat treatment, the residual stress decreases averagely more than 33%, and the tensile strength reaches over 86% of the mechanical properties of forgings. After vacuum heat treatment, the residual stress decreases averagely more than 43%, and the tensile strength reaches the mechanical properties of forgings.

Protective layers can not fit well with the surfaces of the materials due to the surface roughness of the K24 nickel based alloy is high. So the laser shock processing without coating (LSPwC) is carried out on the K24 alloy and the high cycle fatigue tests are conducted to verify the reinforcement effect. The mechanisms of the residual stress and microstructures to fatigue performances are discussed. The results show that, compared with the untreated specimen, the fatigue strength of the specimen treated by LSPwC is improved by 16% and that after heat preservation is improved by 11%. Under the effects of the compressive residual stress and high density dislocations that induced by LSPwC, the fatigue performances of the specimens are improved. After heat preservation, the majority of compressive residual stress release, the dislocations have great stability, and this is the main cause of the high cycle fatigue performance improvement.

Combining hollow laser beam inside powder feeding technology and 6-axis robot, a cantilevered thinwalled metal part is deposited layer by layer by means of continuously varying the attitude of laser cladding nozzle along the tangential direction of the thin wall. The modeling of force and displacement of the molten pool on an inclined surface is carried out. The shifting and flow of the molten pool are restrained by optimizing the laser cladding parameters in this model. The experimental results indicate that the forming of the cantilevered part with a changing incline angle from 0° to 81° is achieved without support. And, the surface of this part is flat and smooth, and the“step effect”is completely eliminated. The cladding layers are nearly symmetry along the central axis of the part, and the shifts of the layers influenced by gravity are not apparent. The microstructures of the part at different incline angles have no significant differences, and all achieve small grain size and compact texture.

In order to simultaneously improve the high-temperature wear and oxidation resistance of Ti6Al4V alloy, the composite coatings are prepared on the surface of Ti6Al4V alloy by laser cladding with the precursor mixed NiCr/Cr3C2- Al- Si powder. Microstructure, wear and high temperature oxidation resistance of laser cladding coatings are analyzed. The results show that TiC, Ti5Si3 and Cr3Si particulate reinforced γ - Ni/Al8Cr5 matrix composite coatings are formed. The average micro- hardness of the composite coating is 750 HV0.5, and is almost twice as much as that of Ti6Al4V alloy. At room temperature, compared to Ti6Al4V alloy, the composite coating exhibits excellent tribological property due to its high hardness. While at high temperature of 600 ℃ , the formation of protective transferred layers between the sliding surface of Ti6Al4V alloy and the ceramic couple can play a positive self-lubrication role. Compared with the Ti6Al4V alloy, the wear resistance of the composite coating has slight decrease because of the formation of micro-cracks on the worn surface at high temperature. After isothermal oxidation tests at 800 ℃ for 32 h, the Ti6Al4V alloy is oxidized quickly because of the high affinity of Ti towards O and the non- protective oxide scales of TiO2. The composite coating can form continuous Al2O3, NiO and Cr2O3 oxide scales on the surface, which is more protective than TiO2. The high- temperature oxidation resistance of the laser cladding composite coating is approximately 8.4 times higher than that of the Ti6Al4V alloy.

To improve the surface properties of AZ80 magnesium alloy, the laser cladding of the preplaced Al63Cu27Zn10 (atomis fraction, %) powder on magnesium alloy is carried out under low-temperature water cooling condition. The microstructure and properties of the coating are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS), microhardness tester, abrasion tester and electrochemical workstation. The results show that the cladding layers are well bonded with the substrate and are composed of α-Mg, binary phases Al17Mg12, AlMg, Al3Mg2, ternary phases Mg32Al47Cu7, AlMg2Zn, MgAl2O4 and amorphous phase. The microhardness of the cladding layer ranges from 375 to 683 HV，which is 4~7 times higher than that of the AZ80 substrate (92 HV). The relative wear resistance of the cladding layer is 3.2 times than that of the substrate. The corrosion potential (Ecorr) is increased with 389.5 mV and the corrosion current is decreased by two orders of magnitude. After the laser cladding Al63Cu27Zn10 (atomic fraction, %) layer, both wear resistance and corrosion resistance of the AZ80 substrate are greatly improved.

Based on the internal powder feeding technology, laser forming of variable laserhead space posture/direction in the laser accumulation process is realized with 6-axis robot. The effects of continuously variable spatial angle of substrate on the cladding morphology are studied. The difficulties and key technologies of spatial variable posture in laser accumulation process are analyzed. Laser forming experiment of a metal part with continuously varying spatial angle of laserhead is conducted. The formed part microstructure, thickness and microhardness are analyzed. The experimental results show that the offset of cladding layers increase and the max value of offset is 0.06 mm. The difficult of space variable posture laser accumulation are solved effectively by tangential layering technology, axis offset compensation technology and cladding layer growth adaptive technology solve. The formed part combines well with the substrate metallurgy. The microstructure of the“vase”is dense and uniform relatively, and the overall microhardness value changes small. At large angle changes, the microstructure of formed parts has some porosity and slag, and with a larger microhardness decline. At small angle changes, microhardness has no clear downward.

Laser paint removal mechanism is studied by analyzing the morphology and element composition of the ejected particle coming from nanosecond Nd∶YAG pulse laser radiation. The scanning electron microscope results show that the micro-/nano-particles, web-like aggregates are produced respectively in the process of laser paint removal. Micro- particles have irregular shapes and rough surfaces while nano- particles exhibit spherical and smooth surfaces. The average sizes of micro-and nanoparticles become larger as the laser energy increase. The energy dispersive X-ray spectrometer results indicate that the components of micro-particles are the same as the bulk material, related to the vibration removal mechanism. However, the content (atomic fraction) of C element for nanoparticles decrease seriously, more than 50%, resulting from the effect of laser ablation to paint. The research provides a new idea and method for studying the basic physical mechanism of laser paint removal.

To investigate the influence of Nd∶YAG laser gingival retraction techniques on gingival retraction and the impact of painful reaction and periodontal local health in comparison with two- gingival retraction cords, 96 teeth are selected in clinic randomly and divided into two groups, two- gingival retraction cords group and Nd∶YAG laser gingival retraction group, observing the plaster model, impression and painful reaction. The periodontal parameters are evaluated and analyzed statistically after one week, one month and three months. The plaster models and impressions in these two groups are satisfying. The no pain rate in Nd∶ YAG laser group is significantly higher than that in the two- gingival retraction cords group, the difference is statistically significant (P0.05). The treatment time of the Nd∶YAG laser group is significantly shorter than that in the two- gingival retraction cords group. These two methods can both reach ideal clinical effect. But the Nd∶YAG laser gingival retraction technique has shown better features in operation, time consuming and painful reaction.

A method is proposed to use cross-correlation to measure the spatial transverse flow rate. By setting the scanning patterns X and Y based on the spectral domain optical coherence tomography, the absolute value of the flow rate is obtained according to the mathematical relation of the cross-correlation between the adjacent Ascans with the spatial transverse flow rate. The measuring principle of this method is elaborated. The transverse flow rate component distribution of the cross section is described through the simulation experiment using a capillary. It is demonstrated that the measured mean value of the transverse flow rate is in accordance with the set value using the syringe pump.

Based on the need of compensating middle and low order aberrations which lie in solid high power laser system in the future, optimal design and simulation analysis about edge-driven mirror are done. The design frame of four-arm edge-driven mirror is put forward, and the simulation model is built. Aimed at the residual error root mean square (RMS) and peak to valley (PV) value, the influence of structural parameters on the performance of correcting low order aberration is analyzed. According to the residual error RMS and PV value curve of correcting focus astigmatism, coma with structural parameters changing, the optimal parameters of the model are chosen and corresponding residual error RMS and PV values are shown. The simulation and calculation results show that for focus at 20 μm, astigmatism at 10 μm and coma at 10 μm of PV, the residual error correcting focus, astigmatism and coma are 0.2366 μm of RMS and 1.3762 μm of PV, 0.0112 μm of RMS and 0.1146 μm of PV and 0.1606 μm of RMS and 0.9773 μm of PV, respectively. These data prove that correction performance of four- arm edge- driven deformable mirror satisfies the demand of design.

Considering the wavefront aberration and speckle noise in laser active imaging, the influence of speckle noise on wavefront correction based on image metric optimization is discussed. The effect of speckle noise on wavefront correction is researched by simulating the trends of image sharpness value with the root-mean-square (RMS) value of wavefront under different speckle noise level. Based on that, conclusions are verified by the numerical simulation of atmospheric turbulence wavefront close-loop correction. The results show that, with the increase of speckle noise, the monotonicity and linearity between image sharpness metric and the wavefront RMS value are significantly worse, especially while the RMS value is less than 1 rad, so that the convergence speed and the final accuracy are deteriorated. Moreover, when the speckle noise is large, with the increase of wavefront distortion, the effect of speckle noise on the correction performance is much more remarkable.

Stray light is one of the most important factors that affect the image quality of optical system, thus the analysis and suppression of the stray light becomes a significant part in the design processes of the modern infrared optical system. According to the requirements of stray light, the configuration of the space-borne infrared optical system is determined; the sources of the stray light is analyzed, and then point source transmittance (PST) is taken as the standard to evaluate the analysis; the methods of the stray light suppression are designed, such as baffle, vanes, occulters, stops and material; the model of the system is established and its stray light is analyzed with TracePro, and then the PST curves of the system are calculated. The results indicate that the thermal emission of the system is 1.53×10-3 W/m2; the PST curves of the system are declining, at off-field angle ±3°, the PST of the system arrives at 10-3~10-5, stray light suppression of the system satisfies the requirements of the image quality.

Large aperture long focal length lens is one of the necessary optics in the high power laser device.Along with the device upgrading, it proposes detailed transmission wavefront including transmission peak valley (PV)、 transmission root mean square gradient (GRMS) for long focal length lens. According to the long focal length characteristic, this paper put forward an interference detection method, which utilizes a collimatied lens and a compensative lens to shorten the optical path length of the long focal lens detection and compensate the theoretical sphere aberration. Zemax is utilized to analyze and optimize the theoretical error and the distance adjustment error of the detection method.This method significantly shorten the optical path length of the long focal lens detection from 13 m (or 33 m) to about 5 m. The results show the transmission wavefront aberration of the tested lens.

In high-power fiber laser beam combining systems, the large beam-pointing errors, which are induced by limited precision of assembling, thermal deformation of mechanism and so on, will affect combining effects and bring serious damages to the systems. Beam-pointing experimental setup with two adaptive fiber-optic collimators is established, the large beam-pointing errors between combined beams are corrected using the stochastic parallel gradient descent control strategies based on variable power- in- the- bucket metrics and divergence metrics, respectively, and 200 W incoherent beam combining is achieved. This work is helpful for the high-power fiber laser beam combining in large pointing-error conditions.

Radio over fiber (RoF) system is a research hotspot of optical communication in recent years. Suppressing the three order intermodulation and improving spurious-free dynamic range are (SFDR) important optimization objectives in RoF system. In order to improve the dynamic range of RoF system, a new scheme which is based on a fiber Bragg grating notch filter and a tunable delay line (TDL) to realize the three order intermodulation suppression is proposed. After theory analysis to this scheme, an experiment is made to verify it. The experimental results show that it can effectively suppress the three order intermodulation and improve the system's dynamic range by 10.5 dB. In addition, this scheme has the advantages of simple structure and low cost.

A novel construction method of full rank quasi-cyclic low-density parity-check (QC-LDPC) codes is proposed based on base matrices and masking matrices for efficient use of low-density parity-check (LDPC) codes in optical communication systems with the systems′ characteristics. First, a base matrix based on which circulant permutation matrices and parity-check matrices with girth at least eight are extended out is defined. Then, the parity-check matrices are transformed using the masking matrices which are designed by the proposed theorem. Finally, full rank QC-LDPC codes with girth at least eight are constructed. Compared with different construction schemes in theory analysis and bit error rate performance, results indicate that the proposed LDPC codes are full rank with strict quasi-cyclic feature and excellent error correction capability. The construction method is flexible. As a result, the proposed QC-LDPC codes are suitable for the optical communication systems.

Under Gamma-Gamma atmospheric turbulence, the influence of atmospheric scintillation, channel loss and pointing error on the performance of differential phase shift keying (DPSK) coherent optical communication system such as the bit error rate (BER), channel capacity and outage probability is studied in detail. Free space optical communication (FSO) system is based on the Mach- Zehnder modulator (MZM) and Mach- Zehnder interferometer (MZI) DPSK modulation/demodulation structure. The closed- form expression of average BER, average channel capacity and interruption probability is derived by the generalized hypergeometric method and the simplified analysis. The simulation is taken place under the Matlab platform. Numerical results show that the average BER and channel capacity are decreased with the atmospheric turbulence increased, the channel capacity can be promoted by increased the bandwidth or reduced the jitter variance, and the communication performance of the system is seriously affected by the increasing outage probability owing to the overlarge pointing error.

The transmission spectral characteristics of the cascaded tilted long period fiber grating (CTLPFG) are studied theoretically and experimentally. Based on the coupled-mode theory and transfer matrix method, the effects of cascading lengths, cascading location, the number of cascades and tilt angle on CTLPFG transmission spectrum are simulated. The transmission spectrum of the CTLPFG is consistent with the transmission spectrum of the cascaded long period fiber grating (CLPFG) in cascading length and cascading location. The loss peaks of the second and 3rd- order cladding modes increase as the tilt angle is enhanced, and the second- order cladding mode is stronger than the 3rd-order mode. The second-order transmission spectra are sensitive to changes in the inclination for the angle above 60°. The width of the pass-bands increases along with the increase of the cascaded segments number, and they are in linear relationship. The results show that CTLPFG has a good value in a bimodal filter. CTLPFGs are made in experiments through point by point. Experimental results and theoretical simulations are comparatively analyzed, which demonstrates that they are in favorable consistency.

A phase interrogation algorithm with high resolution for the measurement of the polarization nonreciprocal phase-shift of hybrid Sagnac interferometers is proposed. Taking wavenumber instead of wavelength as the function variable, the output spectrum is a standard cosine spectrum function. The frequency, interference order and relative phase of this spectrum function can be obtained after Fourier transform and inverse Fourier transform. And then the measurement of the polarization nonreciprocal phase-shift of hybrid Sagnac interferometers can be realized with high resolution and a large rangement. A typical hybrid Sagnac interferometer based polarization maintaining fibrer(PMF) temperature sensor is built and the absolute phase is determined with proposed algorithm. Experiments show that less than 0.1 ℃ temperature resolution is realized and the temperatures from room temperature to 900 ℃ can be measured with a good linearity.

As the investigation is deepened, it is necessary to measure velocity with different techniques based on single probe to a point in the fields of shock waves physics, explosion physics, weapon, intense laser, and so on. The operational principles，optical structures and synchronous measuremental problems of the conventional and heterodyne photonic Doppler velocimetry (PDV) techniques are analyzed. According to the analysis, a novel velocimetry based on single probe, which can measure a target′s velocity by different techniques, is designed and assembled.The aluminum flyer plate and a large number of lead granules loaded by detonation wave are tested by the proposed velocimetry. The experimental results show that the velocities of single or multiple targets are measured well by the novel velocimetry, and the speed curves of the targets under test are obtained in independence measurement by two techniques. The research results can provide a valuable reference for the practical application of the velocimetry to measure a target′s velocity with different techniques simultaneously.

Aiming at the high speed sliding electrical contact rail, the surface micro damage detection and identification method are studied. Based on the principle of laser scanning, a three-dimensional measurement system is constructed for acquisition of point cloud information for rail surface, meanwhile a method of depth mapping color based on point cloud is proposed for the detection of rail surface micro damage. After the threedimensional point cloud data being denoised, smoothed and reduced, according to the datum plane set, point cloud depth mapping color model is constructed, the point cloud depth information can be mapped into red, green, blue (RGB) information, and the optimum color threshold is set by using the one-dimensional maximum entropy method to realize the accurate extraction of the damage area. Binary tree pattern recognition method is used to establish damage classification model and realize the identification and classification of rail surface micro damage. The results show that detection rate of the micro damage of which mass loss is less than 1 gram is more than ninety-eight percent, detection accuracy of minor mass loss is milligram and the damage identification rate of pits and scratches can reach above eighty percent.

SiC crystals are used for a high refractive index material, as the frequency-selected device of Brewster plate. A stable single- longitudinal- mode green laser with an output power of 120 mW is achieved. Both the theoretical analysis and experimental results show that, compared with the common frequency-selected device using K9 glass as Brewster plate, the new frequency-selected device using the high refractive crystal of SiC as Brewster plate makes it easier to adjust the entire optical system. Moreover, the device works more stably, be much easier to achieve commercialization.

The influence of Mn、Mo、Ti additions on the microstructure and magnetic properties of FeNiCr/60%WC composite coatings produced by laser cladding are investigated. The microstructure, composition and phase of FeNiCr/60% WC coatings are characterized using scanning electron microscopy (SEM), transmission electron microscone (TEM) and X-ray diffraction (XRD). The magnetic properties of the composite coatings are examined by a vibrating sample magnetometer (VSM). The results show that there′s good metallurgical combination between WC- FeNiCr composite coatings and substrate, no defects on the surface such as porosity and crack. With the addition of Mn, Mo, Ti, the metallurgical reaction and microstructure is more complex, there′re interaction between elements of Fe, Ni, Cr and mutual fusion diffusion with WC, generate new non-magnetic phases TiC, MoC, Fe-Cr (sigma), Cr0.19 Fe0.7 Ni0.11. And that with the addition of Mn, Mo, Ti, composite coating′s relative permeability decreases significantly, and magnetic has strong stability.

Experiment of warm laser shock peening (WLSP) of AZ80-T6 magnesium alloy at room temperature to 300 ℃ is carried out using Nd: glass laser. The results show that WLSP has obvious warm strengthening effect and generates higher residual compressive stress compared with LSP at room temperature. Surface compressive residual stress (-150 MPa) and micro-hardness get to the highest value at 150 ℃. Micro-hardness is improved by 35.8% compared with the substrate, showing the best warm strengthening effect. While the surface micro-hardness tends to be a stable value ranging from 122.1 to 119.1 HV at 150 ℃~250 ℃, exhibiting a good thermal stability. The three dimensional (3D) profile, surface morphology and surface roughness of the laser shocked craters at different temperatures are analyzed and discussed.

The GaN epitaxial wafers with a p-GaN surface are irradiated with an excimer laser at different energy densities and pulse numbers. The laser irradiation induced changes in optical and electrical properties of GaN epitaxial wafers are examined using photoluminescence, cathode luminescence, X-ray photoelectron spectroscopy, Hall, I-V characterization. Experimental results show that under an appropriate laser irradiating condition and annealing treatment in N2, the luminescent and electrical properties of the samples are improved to different degrees. The irradiated and annealed samples are transformed into light emitting diode (LED) device with semiconductor packing process, and the relationship between the luminescent properties of LED and the laser energy density or annealing atmosphere are investigated. After laser irradiaiton and annealing treatment, the light output power of GaN- based LED increases at least about 37% compared with non- irradiated samples, which shows that the improvement of the electrical properties of GaN epitaxial materials plays important role in enhancing the luminescent properties of the LED device.

A distortion correction method based on ray tracing of test optics is proposed. The position of the symmetric distortion center and the sampling interval of the test wavefront are solved by extraction and analysis of the surface boundary, then the relationship between the mirror under test and the surface map is established by ray tracing to correct the distortion. The 730 mm ×268 mm primary mirror of an off-axis threemirror optical system is tested by null lens, and this method is applied to correcting the distortion of the surface maps. After correction the maximum of the standard correlation function between the binary map and the binary mirror image increases from 0.925 to 0.985, the improvement is conspicuity.

In order to satisfy the demand of the measurement for reflection phase retardation with high precision in a short time, a measuring system based on the typical optical structure which is composed of polarizer, prism and analyzer (PPA) is presented. By means of least-squares method, a binary linear analysis is employed to fit the intensity distribution points which are captured without knowing the initial analyzer angle. Then, two sets of intensity distribution points captured under the different conditions of polarizing angle are processed with the methods of repeated fitting and approximation to obtain an intersection, which is just the measured value of reflection phase retardation. In this approach, data collection of the intensity distribution as well as the associated numerical calculation can be performed via software system without setting optical elements′ azimuth accurately. Moreover, all of the measuring operations can be completed in 15 s. The experimental results show the error of the measured result of reflection phase retardation is 0.005 rad and the repeatability of which is 0.0016 rad as well.

The existing infrared target detection algorithm in compressive domain achieves obtain good performance with low required data storage, but have its own shortcomings. One shortcoming is the difficulty to estimate background parameters, which are sensitive to noise and complex background, the other is the high false dismissal probability when targets are close to their neighbors. Considering those shortcomings, an infrared small target detection algorithm in compressive domain based on self- adaptive parameter configuration and noise statistics is proposed. The original infrared image is projected on a sensing matrix to obtain the measurement vector. The sparse target matrix and the low-rank background matrix can be recovered and separated simultaneously from the measurements based on low- rank and sparse matrix decomposition in compressive domain with adaptive parameter. The infrared small target detection is realized by threshold segmentation of statistical model of noise. Results indicate that the proposed method outperforms the previous method in both subjective and objective qualities under complex infrared background with less data storage, and solves the false dismissal probability problem when targets are close to their neighbors.

A technique combined multi-wavelength phase-shifting interferometry with principal component analysis (PCA) is presented. By using a monochrome CCD to simultaneously capture a sequence of in-line phaseshifting interferograms with random and unknown phase shifts at multiple wavelengths, the wrapped phase information of each wavelength can be constructed through using the PCA algorithm. Then an unambiguous phase of an extended synthetic beat wavelength can be determined by multi-wavelength optical phase unwrapping and noise reduction. Both the numerical simulation and experimental results show the simple optical measurement process, fast computing speed and high resolution of the proposed method.

A new type of randomly encoded hybrid grating for wavefront testing by quadriwave lateral shearing interferometry is proposed. The randomly encoded hybrid grating which includes an amplitude encoded grating and a phase chessboard is obtained according to the Fraunhofer diffraction principle and the randomly coding method based on the quantization of radiant flux. Compared with the modified Hartmann mask (MHM), only four diffraction orders exist in its diffraction field, and the quadriwave lateral shearing interferometry is better achieved. System parameters such as the incident beam diameter, grating pitch and the distance from the grating to the imaging plane are analyzed and determined. Comparing the far-field intensity distribution and quadriwave lateral shearing interferograms of the randomly encoded hybrid grating with MHM, results show that only four spots with equal intensity exist in the far-field diffraction of the randomly encoded hybrid grating; the shearing interferogram is stable, and it is capable of detecting arbitrary wavefront aberrations.

A back-scattering fluorescence spectrum technique for recognition of petroleum and lubricant is developed by use of 532 nm exciting wavelength laser. It is shown that the ratio of back-scattering fluorescence intensity to the scattered main laser intensity depends strongly on the oil type and the incident angle. To enhance the feature of oil type, the ratio data of 45° and 60° incidence are fused in a 2D spectrum. Then the 2D spectrum is divided into two areas, the oil type can be determined according to which area the measured ratio data lie in. The experimental results show that the correct identification probability can be as high as 92%. It is expected that the proposed method can be a useful technique for oil type recognition.

The velocity of gas flow field is measured by using Fabry–Perot etalon to detect the Doppler frequency shift of molecular scattering. The working principle of velocity measurement system is introduced. The effects of performance of Fabry–Perot etalon and change of environmental temperature on the velocity measurement are analyzed. The multi-point velocity measurement system is set up. The unshifted incident laser signal and the shifted Rayleigh scattered signal are recorded simultaneously in order to eliminate the effect on the velocity measurement when the positions of interference fringes are changed due to the change of environmental temperature. A couple of large aspherical lens are used to enhance the taking intensity of Rayleigh scattering signal. Through high precision data transform means, the multi-point velocity results of high speed cold crossflow are obtained. The research results show that this method has the capability for velocity measurement of gas flow field with high dependability.

Evaporation is ubiquitous in nature and engineering. The direct measurements of vapor transport during evaporation are of great importance. A tunable diode laser emitting at around 1370 nm is used to in situ detect the water evaporation from a free water surface subject to crossing wind at various velocities. Results show that the observed profiles of water vapor partial pressure agree with the prediction of the similarity principle, with overall deviation less than 4%.