Realizing beam cleanup using adaptive optics technique is an important research field of the high energy laser systems. To arrive at the aim of miniaturizing and low cost of the beam cleanup system, the method of wavefront distortion correction based on model-free optimization of the system performance metric is an appropriate scheme. This paper researches the application of the stochastic parallel gradient descent (SPGD) optimization algorithm on the beam cleanup system. Numerical simulations of the SPGD wavefront correction of phase aberrations commonly found in high energy laser beams were first carried out. Above this, an experimental 37-element adaptive optics beam cleanup system was set up and the influences of the two-sided perturbation method and the adaptive change of the iterative gain coefficient were studied on the convergence performance of the algorithm. The results of the numerical simulation and experiments verify the ability of the SPGD wavefront control method to correct different strengths of wavefront distortions and indicate the feasibility of the SPGD beam cleanup method.

In order to analyze the performance of linear phase retrieval (LPR) sensor, an experimental setup based on the LPR method has been built. The measurement and wavefront retrieval of LPR sensor and Hartman wavefront sensor were compared on the same stochastic wavefront aberration. The influence of different detection resolution and Zernike retrieval order on retrieval results has been compared and analyzed. After analyzing the target resolution, it is considered that reasonable target size will benifit retrieval precision. At the same time, the LPR sensor can realize similiar precision measurement with less detection cells. With a target resolution of 8 pixel×8 pixel in experiment the error coefficient is small. The retrieval results of different orders, show the error ratio is less than 0.25 and it is comparatively accurate to retrieve pre-35 order aberrations.

Chinese ocean color and temperature scanner (COCTS) is the main sensor on the Chinese ocean color series satellites, which is used for real-time monitoring of the ocean color and sea-surface temperature of the sea areas around China and part of the global ocean. The calculation of atmospheric diffuse transmittance is required in the ocean color atmosphere correction which affects the accuracy of the atmosphere correction and ocean color information retrieving. An exact computation method of atmospheric diffuse transmittance is developed based on the vector radiative transfer equation (VRTE) which is solved by adding-doubling method. Comparison with the diffuse transmittance derived from SeaWiFS exact diffuse transmittance look-up table, proves that the relative error of this adding-doubling method is less than 1.5%, and when the observing zenith angle is less than 60°, the relative error is even less than 0.5%. Therefore, the adding-doubling method can be used to generate the exact atmospheric diffuse transmittance look-up table for the Chinese ocean color and temperature scanner (COCTS). Finally, using the developed vector radiative transfer code with adding-doubling method, we generate exact atmospheric diffuse transmittance look-up tables for COCTS.

The polarization-sensitive material is fabricated with nematic liquid crystal doped with 0.2% (mass fraction) of azobenzene side-chain liquid-crystalline polymer, in which polarization holographic grating with circular anisotropy was recorded by two orthogonal circular-polarization light beams. It found that when the probe beam is linearly polarized, the ±1 order diffraction beams are also linearly polarized with polarization direction perpendular to that of the probe light and the zero-order diffraction light. The experimental results are in good agreement with the theoretical expectation based on Jones matrix. The diffraction orders can be controlled by the applied electric filed, and there is 90°phase difference between the ±1 orders diffraction beams. When the frequency is 6.05 Hz and the applied voltage is 2.2 V, the extreme value of diffraction orders oscillates.

An interleaver combining ring resonator with Mach-Zehnder interferometer (MZI) is proposed. Based on the phase modification provided by the ring resonator, a maximum flatness filtering response is obtained by optimizing the coupling angle of resonator. Compared with the traditional MZI, the isolation in stopband (>38 dB) and the rolloff in transition band are strengthened, but also the dispersion in passband is reduced to ±10 ps/nm in the center frequency range of 15 GHz which eliminate the distortion of transmission signals. Furthermore, the influences of ring circumference (Lr) on length difference (ΔL) of MZI arms are investigated, and the bandwidth allocation of odd-even ports is directly determined by Lr/ΔL. The result demonstrates that a novel interleaver with 1∶2 asymmetric bandwidth allocation can be achieved by adjusting Lr/ΔL=1/2. This kind of interleaver will make system upgrade from 10 Gb/s to 10 Gb/s+40 Gb/s in a more simple and flexible way.

The channel capacity of coherent pulse-position modulation (PPM) and maximization conditions of information transmitting rate were analyzed. After the probability distribution of the PPM signal detected by heterodyne method is analyzed, the transition probabilities matrix and capacity of optical pulse-position modulated channel with coherent receiver and maximum likelihood detection were deduced. It is proved that under the circumstance of shot-noise limit detection, the capacity of the channel is only related to number of received photons and the PPM order. Jensen′s inequality is used to simplify the capacity of the channel and obtain its low limit, which is close to the capacity of the channel of practical communication link. The relation of the optimum order of coherent-PPM corresponding to the dead time for the greatest transmitting rate is estimated. General relationship between the optimum PPM order and the dead time was given. Using the proposed method, the estimated PPM-order can realize the maximum capacity of channel when received photons can promise the symbol error rate lower than 10-2.

Multiwavelength fiber laser is a perfect light source for future wavelength-division-multiplexing optical communication systems. A multiwavelength fiber laser based on nonlinear polarization rotation with up to 18 wavelengths has been proposed and demonstrated. The intensity- and wavelength-dependent loss induced by nonlinear polarization rotation effect is used to alleviate the mode competition in the homogeneous broadening gain medium of erbium-doped fiber. Instead of traditional filters, a polarization-maintaining fiber is inserted into the laser cavity, with which the polarization-dependent isolator composes an equivalent Lyot birefringent fiber filter. The in-line birefringence fiber filter is used to simplify the laser configuration, which benefits systematic integration. The effect of the 980 nm pump power on the multiwavelength generation is investigated. It is shown that the pump power contributes a lot to the evenness of the multiwavelength spectra due to the intensity dependene of nonlinear polarization rotation effect.

Compared to bipolar sequences, orthogonal quaternary phase sequences are more suitable for optical code devision multiple access (OCDMA) passive optical network (PON) with multi-users for its larger capacity and better cross-correlation character. A orthogonal quaternary phase OCDMA en/decoder based on superstructured fiber Bragg grating is proposed and realized. The proposed en/decoder adopts family A four phase sequences as its address codes and obtain equivalent performance compared to the traditional en-decoder while it needs only one uniform phase board during its fabrication. In order to be compatible to different channels, a novel coding technology is proposed which can encode the user's data with a changed channel. Simulation results show that the en/deconders have higher frequency spectrum efficiency and therefore better en/decoding performance. A 2.5 Gb/s, 156 Gchip/s en-decoding experiment is performed using an en-decoder with its code length 63 and length 4.1 cm, and good en/deconding results are achieved.

Iterative process of error-reduction algorithm is anlyzed, the phase-only object function is obtained when the amplitude of object function and the amplitude of its Fourier transformation are known, and the amplitude and phase of object function are retained as much as possible. The binary coding of cosine is presented to generate binary hologram, and namely transmittance of hologram is 0 or 1 . The phase-only hologram is reconstructed via digital micromirror device (DMD ) hologram display system, and the result proves the effect of reconstruction. The diffraction efficiency of digital micromirror device is analyzed theoretically, and the diffraction efficiency is only related to the ratio of interval size and side length of digital micromirror device. The binary coding of cosine eliminates zeroth order diffraction theoretically, and can generate high pixel hologram.

Sun glint masks real physical properties of water and severely interferes with the acquisition of underwater characteristics. Based on the difference between the glint-contaminated pixel and nearby nonglint pixel, the atmospheric absorption feature which can be used to tune the input parameters of the atmospheric radiative transfer model is obtained, then the atmospheric transmissivity is calculated, and the major factors which influence the degree of glint contamination are discussed in detail. According to the fact that the water-leaving radiance value in near-infrared bands is negligible, the spatial distribution of the glint contamination is solved, the glint is removed, and the non-contaminated image is displayed. It is applied to extract the water-leaving radiance, and the experimental results prove the validity of this algorithm.

The tea quality level was estimated with hyperspectral imaging technology. A hyperspectral imaging system based on spectrometer was developed to perform acquisition of hyperspectral imaging data. The principal component analysis (PCA) was performed to select three optimal bands images. Then, six texture features (i.e., mean, standard deviation, smoothness, third moment, uniformity, and entropy) based on the statistical moment were extracted from each optimal band image, thus 18 variables for each tea sample in all. Finally, PCA was performed again to compress 18 features variables, and 8 principal components (PCs) were extracted as the input of back propagation (BP) neural net. Experimental results showed that discriminating rate was 97% in the training set and 94% in the prediction set. Overall results sufficiently demonstrate that the hyperspectral imaging technology can be used to estimate tea quality level.

Panoramic annular lens (PAL) which integrates refraction lens and reflection mirror, can capture the super-view field of the entire 360° around the optical axis instantly. It is widely used in robot navigation, video surveillance and virtual reality. The imaging principle of PAL is to project the view field around the optical axis onto an annular plane through twice reflection. There is serious distortion in the tangential and radial directions on the image. A spherical perspective projection model is proposed to correct the image distortion according to the imaging feature of PAL. Firstly, the PAL correction model which includes distortion parameters is constructed. The points on the spatial line are projected to the points on the sphere under this model. All spherical points are fitted to the best great circle by genetic algorithm. The distortion parameters are obtained during this procedure. Then the panoramic image is corrected. Simulation and real-image experiments demonstrate that the tangential and radial distortions are corrected greatly.

image processing; image fusion; contourlet transform; fusion rule

Exit pupil wavefront of the segmented mirror synthetic aperture optics (SAO) is discrete, which is much different from traditional systems. Two methods are used to evaluate SAO systems imaging. One is to get the exit pupil wavefront by interferometer and fit it into Zernike polynomial directly, then use the way of fast Fourier translation (FFT) to get system′s modulation transfer function (MTF); the other is to integral the sub-exit-pupil′s wavefront respectively, and calculate the complex amplitude distribution of each sub-mirror′s, and overlap them in image plane, then get the MTF. As the fitted Zernike polynomial of exit pupil wavefront cannot express the discrete wavefront accurately, the former way is much different from the reality system. A segmented mirror system with three sub-mirrors primary is built, and the wavefront is obtained by ZYGO GPI interferometer, include overall exit pupil wavefront and each sub-exit-pupil wavefront. The two methods are compared, and the result shows the latter way is more precise but complex, and need much more computation; especially, the other more precise polynomial should be used to express the exit-puil wavefront of abnormity figuration sub-mirror, can we get the more rensonable resnlt.

The performances of three kinds of spatial arrangement for the optical synthetic aperture imaging system with four sub-apertures are analyzed. Based on the criterion of avoiding the loss of the effective spatial-frequency information, the restrictive conditions of the spatial arrangement are calculated, and then the effective frequency coverage range and the equivalent aperture are obtained. The results shows that three-arm arrangement is adopted as long as the requirement of frequency coverage range is relatively high; when the frequency coverage range of the three-arm arrangement and the annular-uniform arrangement is equal, the former is better than the latter based on the criterion of the secondary peak depression. When the frequency coverage range of the three-arm arrangement and the annular-optimization arrangement is equal, the point spread function of the annular-optimization arrangement is larger than that of the three-arm arrangement, and the optical transfer function of the annular-optimization arrangement is lack of symmetry of three-arrangement.

The polarizing Michelson interferometer of wind measurement based on polarization arrays is a interferometer for detecting atmosphere temperature and wind velocity. It is based on the principle of polarization interference. Four polarizers whose polarization orientation has an interval of 45° in turn attach to the front of detector. Four beams of light from four-plate pyramid prism pass polarizers. Then four different interferential intensities are formed at the same time on the detector. Then wind velocity and atmosphere temperature will be deduced from the intensities. This imaging process is simulated and emulated. The result after data processing is coincident with true value. The interferometer offers advantages including simple and steady construction and high precision. It is fit for detecting fast goal.

To solve the directionality of spatial magnetic field measurement , two schemes including three-dimensional measurement and simultaneous measurement of transverse, longitudinal components are proposed. The simulation and calculation of three crystals (TbY)IG,Ce∶YIG and YIG by Jones matrix are carried out, and the directionality of magnetooptic glass of MR4 is tested. Both theoretical and experimental results prove the feasibility of the first scheme. For the second scheme the relationship between azimuth angle, ellipticity of the elliptical polarization light and Faraday rotation angle, magnetic linear birefringence is gained, which confirms the feasibility of the second scheme.

In order to improve the measuring precision of spectral line by spectrometer, the parameters of angle dispersive power, line dispersive power and resolving power of spectrometer with grating scanning controlled by computer have been calculated theoretically, and then a method has been put forward to improve the linewidth measurement by two united homogeneous spectrometers. The principle of measuring laser linewidth by two united spectrometers is analyzed theoretically, and the linewidth of He-Ne laser is measured. The experimental results shows amplification factor of full width at half maximum (FWHM) of He-Ne laser spectral line is 3.38×105, and 5 order magnitude of the line width measurement is enhanced at least by the two united homogeneous spectrometers than only one.

In order to limit the error tranfer in wavelet transfrom profilometry, we propose an idea that the amplitude values of wavelet transform coefficients at wavelet-ridge position, which has been ignored before, can be used to guide the phase unwrapping .It means that the wrapped phase located at the pixel with highest amplitude value will be selected as the starting point of the phase unwrapping, and then the pixel with higher amplitude value will be unwrapped earlier. So the path of phase unwrapping is always along the direction from the pixel with higher amplitude value to the one with lower amplitude value. Because of making full use of the amplitude information of wavelet coefficients at wavelet-ridge position, the error transfer is limited within local minimum areas during the process of phase unwrapping .Computer simulation and experimental result verify the proposed idea.

Flowing circulation can emanate heat of liquid laser with single gain host, but it also arises heat gradient in the flowing direction. Double gain host can emanate heat effectively and avoid heat gradient in flowing direction, and possesses better performance. The heat character and far-field facula of liquid laser with single gain host and double gain host at the same gain length were simulated, and then compared. The result indicates the performance of the double gain host is much better than that of the single gain host: the peak intensity of far-field facular is enhanced by ten times, and the energy concentration extent and beam quality are both enhanced evidently.

A novel Q-switched fiber laser made of OptoCeramic electrooptic ceramics is reported. The ring laser is composed with an electrooptic ceramics modulator as Q-switch, highly Yb-doped fiber (peak absorption coefficient at 976 nm is 1200 dB/m) as the gain medium, and pumped by semiconductor laser of 976 nm wavelength. The adoption of highly doped gain fiber shortened the cavity, and meanwhile the output pulse width was compressed. Q-switch is realized from cavity loss modulation, the material refractive index control, which are depondent on the voltage of OptoCeramic element. The influences on output pulses from cavity length, pumping power and repetition rate are investigated. The laser system generates short pulses about 104 ns, with the repetition rate continuously adjusted from 3 kHz to more than 40 kHz.

We propose the concept of partially coherent combining and demonstrate that the linewidth and polarization do not confine partially coherent combination of high power fiber lasers. Numerical calculations show when the linewidths of single fiber laser beam get larger, the far-field pattern almost does not change, but the peak power and Strehl value of far-field spot get smaller, which means the degradation of the partially combined beam. Also we compare the far-field effect of partially coherent and incoherent combination, and the numerical results show that partially coherent combined beam has much higher peak intensity and narrower intensity spot than incoherent combined beam. Partially coherent combined beam still overpasses incoherent counterpart although the combined beam is degraded by a relatively large linewidth.

Stereo-matching is the most important problem in computer vision. Comparing with the binocular vision, trinocular vision can provide more information and an additional constraint of epipolar line to eliminate the ambiguities of stereo-matching. A trinocular stereo-matching algorithm based on adaptive support-weight and disparity adjustment has been proposed to improve the accuracy of trinocular vision. Adaptive support-weight which is an efficient window selection method in binocular stereo is applied in the trinocular stereo. A robust target image selection method is also proposed for using the information of different target images in trinocular stereo-vision system efficiently. So occlusion can be handled well by this means. Furthermore, a trinocular disparity adjustment method is introduced. By using the constraint of color similarity and space proximity, this method can correct many errors of initial disparity. The experimental results show that the proposed algorithm can extract accurate disparity. It′s concise and efficient.

A new method for detecting circles with the characteristic of right triangle inscribed in a circle is proposed. Array storage space based on positions of valid pixels is constructed in order not to search triangles in image space but compressed arrays. By applying special searching algorithms, the complexity of the method is reduced. The procedure searches right triangles in storage space by grades, and then translates the calculation of circle parameters into triangles for the sake of avoiding repeated arithmetic operations and shortening running time. During the work, the proposed method polymerizes single circle parameters efficiently to get the final global results. Experimental results from composite and real images show the proposed algorithm can suppress noise interferences effectively when detecting circles in normal images. Compared with existing methods, it is faster, more reliable, and repeatable, and the accuracy is less than 1 pixel.

The optical properties and the change of Bragg reflected light intensity of the cholesteric liquid crystal in planar texture induced by helix distortion were studied when the applied electric field was perpendicular to the direction of the helical axis. Using LCD matrix optics, Jones matrix method, and Matlab matrix calculation software, reflectance spectra characteristics were analyzed and numerically calculated. According to the numerical and experimental results, the center wavelength of reflected light does not change with voltages and the Bragg reflected light intensity decreases with the increasing voltage. A model of field induced helix distortion was proposed to give the reasonable explanation on the experimental and numerical results. It is also found that the theory for designing the LCD with color change using electrically controlled helix distortion is not feasible.

The samples of Er3+-doped, Yb3+∶Er3+co-doped borosilicate glasses with different dopant concentrations were prepared by the high-temperature sintering technique.Based on Judd-Ofelt (J-O) theory, the J-O intensity parameters Ωk(k=2,4,6), spontaneous radiative lifetime, spontaneous transition probability, fluorescence branching ratio, and spectral line strength of the Er3+ ions were calculated. While the stimulated emission cross sections of the up-conversion red (4F9/2→4I15/2) and green (2H11/2→4I15/2) emission of Er3+ions were analyzed using McCumber theory. The results show that J-O intensity parameter Ω2 becomes smaller with the increase of erbium concentration in Er3+-doped borosilicate glasses. But for the Yb3+∶Er3+ co-doped borosilicate glasses, the value of Ω2 becomes bigger with the increase of ytterbium concentration, and bigger than that of silicate, fluorid, and bismuth glasses reported. The stimulated emission cross sections of the up-conversion red and green emission increas a little.

In order to get reflection surface deformation after assembly of support system, the finite element method (FEM) is used to analyze the primary reflection mirror structure. Surface shape and self-weight deformation of a corbeling system at different tilted angles are analyzed, and deformation displacement on evey pitching height of mirror surface and its corbeling system are obtained. The anlaytical results show at different tilted angles, displacement in Z direction is more than that in X and Y direction, and its maximal displacement is 1.4 μm that translates the reflection surface and changes the focal distance. The deformation of X (slewing axis)direction is 0.01″. And the Y direction is the mirror tilting direction, and its deformation is about 0.5″ and bends the mirror surface.

The Cassegrain system is manufactured with focal length of 6000 mm, and relative diameter of 1/10. The diameter of the primary mirror is 600 mm with its relative diameter of 1/1.2 and the material of the primary mirror is crystallitic glass. Because of even holes on the back of the primary mirror, the lightweight ratio of the primary mirror is 50%. For the reason of large relative diameter and light weight the manufacture of the system is difficult. In the course of the manufacture new methods are developed based on the traditional methods. The support of nine points is used based on the support of three points and finally the primary mirror is made with a high precision. The diameter of dispersion circular of the Cassegrain system is less than 0.02 mm, peak value (PV) of Cassegrain system is 1.23λ (λ=0.6328μm), and the root-mean-square (RMS) value of system is 0.18λ.

Prism-film coupling configuration is a two-prism configuration with one prisms coated with a thin dielectric film. This structure plays an important role in the field of optical signal transmission. The Goos-Hnchen (G-H) shift of reflected and transmitted light beams in this configuration is theoretically investigated by stationary-phase approach. The result shows that the G-H shifts of both the reflected and transmitted light beams oscillate with the increase of the thickness of the thin dielectric film and the angle of incidence. The resonant peaks of reflection G-H shift can be negative as well as positive. The magnitude of the resonant G-H shifts can reach two orders of the wavelength. The above property of the G-H shift modulation may lead to potential applications in new types of optical sensors and devices.

Using spherical wave beam to illuminate an axicon will result in a beam with small central spot and large focal depth, which is useful for laser communication and long-distance measurement. It is possible that the incident spherical wave beam is tilted with the optical axis of the axicon in practical measurement. Based on the Kirchholf diffraction theory and stationary phase method, the diffraction characteristic of an axicon for a tilted spherical wave beam is derived, and the radial energy distribution is also analyzed. Experiment and simulation are performed with an axicon with 15 mm radius and 1° basal angle. The experimental results are compared with the theoretical analysis and computer simulation. Simulation and experiment indicate that decreasing incident spherical wave′s radii of curvature, propagation distance and the tilting angle can weaken the tilting effect on image of diffraction.

A way to measure displacement with chirp fiber grating is proposed based on beam cantilever. When the strain is acting on the cantilever beam, the reflection spectrum of the chirp grating pasted on the cantilever beam is compressed and the displacement can be measured according to the bandwidth of the reflection spectrum. The structure resolves the cross sensitization of the temperature to the displacement measurement. The variation in temperature results in the displacement of the whole reflection spectrum but does not change the bandwidth. The test result shows that this sensor has high accuracy, well linearity and repeatability.

A novel passive homodyne Michelson interferometric fiber-optic hydrophone of anti-aliasing has been manufactured and demonstrated. This new fiber-optic hydrophone consists of a conventional mandrel fiber-optic hydrophone and a metal cylindrical Helmholtz resonator. The acoustic pressure phase sensitivity response has been measured in a standing-wave tube filled with water. Experimental results show that this new fiber-optic hydrophone is of acoustic low-pass filtering, which makes it available for suppressing high-frequency components in acoustic signal and eliminating aliasing in the future sonar system. The low frequency sensitivity of this fiber-optic hydrophone, as determined by the length of the sensing fiber and the performance of the elastic layer, is -159 dB (0 dB=1 rad/μPa). The frequency response has a resonance peak near 1150 Hz, which is determined by the cylindrical Helmholtz resonator. There is a measured roll-off of 50 dB/octave over the range of 1150～2280 Hz. The acoustic sensitivity attenuation beyond 1500 Hz is bigger than 10 dB. This new fiber-optic hydrophone is very important for enhancing the operation performance of the future sonar system.

The initial operating position was set by means of tuning Fabry-Pérot etalon angle, and the accuracy of angle tuning was 10 μrad. At this position the reference signal and echo signal were measured with monostatic polarization light splitting. The longitudinal-mode Nd∶YAG laser with wavelength of 1.064 μm was used with the probability of single longitudinal mode greater than 98%, and long-time stability of laser frequency about 10-7. The hard target was placed at the focal spot of the collimating mirror. The reference and echo signal were separately measured when the hard target was still, in positive rotation and negative rotation. The correction factor about the angle of reference signal is obtained as 1.1949, by the relation between reference and echo signal when the hard target is still. The measured results indicate the velocity error is less than 0.5 m/s between measured value and true value with this correction factor.

The spectral bidirectional reflectance distribution function (spectral BRDF) of mauve and white painted plate are measured in the visible spectrum (400～780 nm). The relationship between variation of spectral BRDF with wavelength and scattering angle and optical characteristics of the measured samples is discussed. With five-parameter model of BRDF and the modified particle swarm optimization (PSO) algorithm, the optimum parameters of the model at each wavelength in the measured spectrum are retrieved at intervals of 1 nm. Spectral BRDF and directional hemisphere reflectance (DHR) of samples calculated with the model are in good agreement with the measured data, which indicates that the means and result of spectral BRDF modeling are doable and reliable. Spectral BRDF of target samples can be used in the research of spectral scattering of objects, which is of great value to the detection, tracking and identification of objects.

Most of the former studies on characteristics of scattered light on large bubbles in water are based on Davis model, in which a bubble is regarded as an uncoated spherical object. However, most of the bubbles in water are coated with oil layer, which surely influences their scattering characteristics. We establish a simplified equation to calculate how a light beam is scattered when it enters a coated bubble. A two-dimensional curve,namely volume scattering function (VSF) is plotted, that models the angular distribution of scattered intensity by a coated bubble with a diameter far larger than wavelength of incident light. The curve reveals the far-field characteristics of light scattered by the coated bubble, as well as the main influence on scattering intensity. By comparing with VSF of uncoated bubble, we discuss the parameters that influence distribution of scattering light on a coated bubble, such as thickness of the oil layer, relative index of refraction and get that oil coating weakens the forward scattering of the coated bubble while strengthens the backward scattering.

Thin films of barium strontium titanate (Ba0.5Sr0.5TiO3) were fabricated by pulsed-laser deposition technique. X-ray photoelectron spectroscopy and atomic-force microscopy were used to characterize the chemical composition and surfacial profile of the films. The permittivity and dielectric loss as a function of applied electric field were conducted with an alternating current (AC) signal of 50 mV at 100 kHz. The obtained value of dielectric tunability is about 45%. The nonlinear optical properties of the films were determined by a single beam z-scan method at a wavelength of 532 nm with laser pulse duration of 55 ps. The results show that Ba0.5Sr0.5TiO3 thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient of 5.04×10-6 cm2/kW and 3.59×10-6 m/W, respectively.

The damage of optical elements is a main limiting factor for a large laser system. The understanding of damage mechanisms can promote system design, choice of operational parameters and technology development. Thermodynamics damage of optical coatings induced by absorbing inclusions was studied based on thermal irradiation model. It is shown that the initial damage time of optical coatings during a laser pulse is very short and the most part of the laser pulse generates larger damage. Considering the phase change of absorbing inclusion, we calculated the gas pressure exerting on coatings due to the gas phase change of absorbing inclusion and discussed the possibility of the macro damage of optical coatings. This model can well interpret the flat bottom pit damage morphology of optical coatings.

To meet the needs of research on new fast scintillation materials, the home-made pulsed X-ray facility for fluorescents lifetime measurement was upgraded by using microchannel plate photomultiplier tube (MCP-PMT), fast preamplifier (FPA) and fast constant-fraction discriminator (CFD). The time resolution of the facility is improved to about 170ps. The decay time measurement of the fast scintillation component in BaF2 crystal shows that the facility can be well adequate to the research on decay times of fast scintillation materials.