The Doppler wind lidar was deployed at Beijing Meteorological Observatory from March to April, 2011 and April to May, 2013, respectively. Laser radar observational case using a modified differential zero crossing method shows a good agreement with radiosonde measurements. The statistic analysis of 167 Zenith-pointing lidar profiles indicates that the averaged frequency of cloud occurrence is 62.9%, which single-layer, two-layer, and three-layer clouds account for 34.1%, 16.2%, and 6.6% of all profiles, respectively. Low, middle, high and deep convective clouds account for 30.2%, 51.4%, 17.3%, and 1.1% of all cloud observations, respectively. The cloud-base height, cloud-top height, and cloud thickness for all clouds are 4.26, 4.99, and 0.73 km, respectively. The occurrence frequency of single-layer cloud is the highest. Among the multi-layer clouds, the thickness of upper level clouds is the thickest, which has same magnitude as the thickness of single-layer clouds during spring in Beijing. Lidar observations are compared with the radiosonde for 61 matched profiles. The validations of the synchronous measurements show that the corresponding correlation coefficients of the cloud-base height and the cloud-top height from the lidar and the radiosonde are 0.86 and 0.83, respectively, and the root mean square deviation are 1.31 km and 1.74 km, respectively. The cloud-base heights from the radiosonde appear systematically higher than those from the lidar.

Based on the extended Huygens-Fresnel principle and Wigner distribution function, the formulas for the propagation factor of anomalous hollow beams in oceanic turbulence are derived and the corresponding numerical calculation and analysis are carried out. The results indicate that the propagation factor of anomalous hollow beams will reduce along the decrease of the transmission distance and the increase of beam wavelength; when the transmission distance is fixed，the propagation factor of anomalous hollow beams will reduce at first, then increase with the increase of beam width; and the beams also reduce at first, and it is invariant in the end with the coherence length increased on the same premise. In oceanic turbulence, the propagation factor of anomalous hollow beams is associated with the kinetic energy dissipation rate, the temperature variance dissipation rate, and the salinity and temperature change ratio. The propagation factor must reduce gradually due to the increase of kinetic energy dissipation rate and the increase of the temperature variance dissipation rate and the salinity and temperature change ratio. These results are useful for the transmission and application of beams in the oceanic turbulence.

To meet the demand for the few-modes optical communication system, a few-mode semiconductor laser based on the compressive strain quantum well structure in InP/InGaAsP materials is designed and manufactured. The device can work in the fundamental mode and the 1st order lateral mode depending on the injection current level. The LP01 or the LP11 modes of a few mode fiber is successfully excited by the few-modes laser. The device is easy to be implemented with low production costs, which provides a new light source choice for few-modes optical communication system. Also this device gives a possibility to realize the integrated emitter in the space division multiplex system.

To investigate the negative effects of the relative intensity noise (RIN) of the Raman pump and the Brillouin slow light on the long-distance Brillouin optical time-domain analyzer (BOTDA) assisted by distributed Raman amplification (DRA), the coupled amplitude equations describing the interactions between the Raman pump, Brillouin pump and Brillouin probe have been solved. Results of RIN transmission of the Raman pump show that 1 dB increase in the RIN of the Raman pump leads to about 1 dB decrement in the signal-to-noise ratio (SNR) of the received electrical signal. This undesirable effect can be ignored when the RIN value of the Raman pump is down to -135 dB. Furthermore, results of Brillouin slow light show that compensating the linear loss of the waves in the sensing fiber by DRA results in an increase of position locating error (PLR) induced by Brillouin slow light effect. It′s also shown that, at the same time, point in the detected signal traces obtained at different sweeping frequencies corresponds to different spatial locations on account of PLR. The errors will have a significant negative effect on the reconstruction of the 3D Brillouin spectrum and the accurate extracting of the Brillouin frequency shift of the sensing fiber.

The working model of ultraviolet (UV) optical communication transceiver is studied. The transceiver response time (TRT) parameter is defined to evaluate the handover efficiency of transceiver. A highly sensitive broadband receiver is designed and developed to measure this parameter. The experimental results show that the TRT of UV communication transceiver is about 100 ms, and the repeatability is less than 1 ms. The results can provide significant data for the research on UV communication.

The principle of the far field distribution measurement of space laser communication terminals based on the Fourier-transform characteristics of lens is analyzed. The influence of test system with spherical and coma aberrations on the far field distribution of the beam is described and simulated. The simulated results show that the spherical and coma aberrations both reduce the maximum power at the receiving plane and the rotational symmetry of field distribution is only influenced by coma aberrations. The maximum power changes by lower than 0.2% with the root mean squares (RMS) developed. The measurement system is analyzed with Zemax-EE software. The analyzed results demonstrate that the RMS aberrations of the test system are below 0.02λ. The wavefront error of a long focal off-axis Cassegrain optical system is less than 0.0001λ in the working wavelength (800~1700 nm) and good diffraction-limited quality is obtained in full field. The experimental results indicate that the maximum dusky ring dimension error is less than 2.5% compared with the theoretical values. These results prove the feasibility of the far field distribution measurement system.

Polarization-maintaining (PM) supercontinuum is generated in an all-PM-fiber amplifier. A tunable fiber pulse laser with the central wavelength 1064 nm is used as the seed of the master-oscillation power-amplifier (MOPA), and the output power of the seed is 80 mW while the repetition frequency and the pulse width are tuned to 5 MHz and 150 ps, respectively. The pulse is amplified through two PM-pre-amplifiers and then coupled into 11 m long double-cladding PM ytterbium-doped fiber (YDF), which has core/inner-cladding dimensions of 25 μm/400 μm and the absorption coefficient of the fiber is 2.2 dB/m at 976 nm. With the pumped power of 355 W, the average power of the supercontinuum generated in the amplifier is measured as 196 W, with the slope efficiency of 55%, while the spectra extend from 0.85 μm to 1.86 μm.

For multiple-phase flow measurement, digital in-line holography has the advantages of three-dimensional （3D）and non-contact. It has been found to be a powerful tool in 3D diagnostics of particle field. A study on large and small particles in gas-solids flow field using a digital holographic system is presented. Firstly, the numerical simulation is conducted to study the precision influence of small particles measurement when large particle is existed in the flow field, and the capability of holography measurement on small particles. Secondly, the recorded particle hologram is numerically reconstructed by using wavelet transform algorithm. The size and spatial distribution of particles are obtained based on identification and 3D location of particles. In the experiments, by using digital in-line holographic measurement system, the particle fields are tested. It is found that the particles in the measurement volume are successfully reconstructed, and the measurement results of particle size distribution agree with the actual parameter. This indicates the feasibility that digital in-line holography is used to measure particle sizing and 3D position with different particle sizes and concentration distribution in multiple-phase flow.

There is plenty of complex ground information in high-resolution remote sensing images. The direct road sementation in the images causes low accuracy and cannot rule out inferences such as residential areas. A road extraction method based on saliency analysis for high-resolution remote sensing images is proposed. The feature map of residential areas and roads is obtained by automatic seymentation. A saliency map of residential areas is obtained using the human visual system. The feature map of residential areas is generated by segmenting the saliency map. Finally, the roads are extracted by the logical exclusion OR operation of the two feature maps. Experimental results show that the proposed method can remove the inference residential areas effectively and extract roads perfectly. It has both theoretical and practical significance for road extraction in remote sensing images in the future.

Binocular stereo matching is an important issue in computer vision research. In order to solve the problem of stereo matching at the depth discontinuities, low textured regions and repetitive structures incidental matching error, a stereo matching algorithm based on image segmentation and improved adaptive support weight is proposed. the initial matching cost that combines the color similarity, euclidean distance similarity, user-defined inter color correlation similarity and gradient similarity is defined. The mean shift algorithm segment matching pixel is used at different depth regions in order to refine the matching cost. Meanwhile, in the process of cost aggregation, the new cost aggregation is calculated based on compare transform matching pixel by ranking transform in stereo image pairs in order to solve the influence of brightness and noise difference between the stereo image pairs, so a more accurate disparity result can be acquired. Finally, the algorithm is tested by Middlebury stereo benchmark on the VS2010 software platform, and the results show that it has better performance than other local matching methods, and its robustness is very strong and has higher accurate matching rate.

The laser disturbing effect under the different F number of optical system has been investigated in the experiment. We measure the noise grey value and its distribution probability of CCD output image under the dark background and no laser disturbing. According to comparing laser spot image and grey scale distribution under the different F numbers, it is found that the pixel number of different grey scales linearly increase with the gradually decrease of F number, not exponentially or logarithmically. At last, the diffraction pattern of pentagonal stop is effectively simulated based on the theory of Fraunhofer diffraction. The simulated results show that laser spot image is just the diffraction pattern of stop at the large F number. The research results can provide technical support and theoretical reference for evaluating laser disturbing effect of electro-optical imaging system under the different F numbers.

We demonstrate a practical femtosecond laser absolute ranging system. High update rate and high precision arbitrary distance measurement can be realized based on nonlinear optical sampling between two free running polarization maintaining femtosecond fiber lasers. A ranging experiment for a cooperative target at about 2 m distance is demonstrated. A 3.3 μm ranging precision at 2 kHz update rate is realized. The ranging precision can reach 0.8 μm at 100 Hz update rate by averaging of continuous measurements. The ranging ambiguity is 2.08 m, which can be removed by introducing a coarse measurement with about 1 meter precision, resulting in an arbitrary ranging with micrometer precision. Due to the usage of all-polarization maintaining fiber based femtosecond laser sources, this ranging system is advantageous of high environmental stability, high compatibility, and maintenance free operation, which is attractive for a number of applications, such as large-scale manufacturing, aerospace engineering and remote sensing.

Using the high precision digital stress measurement instrument, the distribution of stress birefringence (SBR) of optical glass is digitally measured. Experiment shows that the impact of temperature and gravity on the stress birefringence of glass cannot be neglected, compared to the first measurement result, the max value of SBR reduces 83%, and the root mean square (RMS) value reduces 87%. Also, when temperature maintains constant, the effect of gravity is still obvious, experimental result shows that the max value of SBR increases 68%, and the RMS value increases 90% in this situation. The stress birefringence of optical material/glass distribution measurement with high precision has great impact on optical machining.

A numerical model of Q-switched 4-level intracavity frequency doubled laser is proposed based on rate equation, Q-switching and effective energy storage time theory. The calculated peak power, pulse width and average power with repetition rate is derived and compared with experimental results of a Q-switched 532 nm laser. The calculated results fit well with the experimental results during the repetition rate range from 1kHz to 100kHz which shows that the numerical model is valid.

A picosecond erbium-doped fiber laser based on gain-switched laser diode is demonstrated. The gain-switched laser diode seed can produce 80 ps pulses with tunable repetition rates from 100 kHz to 20 MHz. After master-oscillator power-amplifier (MOPA), this fiber laser yields 9.3 W average power at 20 MHz repetition rate, corresponding to 5.8 kW peak power.

In inertial confinement fusion(ICF) laser facility, accurate measurement of the gain uniformity of disk amplifiers is the basis for device design. Based on CCD imaging method, the gain uniformity of disk amplifiers with the average small\|signal gain coefficient is measured about 5.28%/cm on integration\|test\|bed(ITB) laser facility, which is the first laser facility with ten thousand joules output in single beam. Experimental results show that when the average small\|signal gain coefficient is 5.28%/cm, the gain uniformity is 1.091 (maximum /average) within the aperture range, and within the range of 360 mm×360 mm laser beam, the gain uniformity is about 1.061 (maximum/average), which satisfied the 19.6 kJ/5 ns laser output on ITB laser facility.

The parameters of light source in synthetic aperture ladar (SAL) is very important to both the design of system and the signal processing algorithm. As the light source in the SAL, the fiber laser uses PZT stretching the fiber Bragg grating in order to tune the laser frequency. So it is necessary to obtain the deformation and frequency response of PZT pipe driven by sawtooth voltage of different periods. Accordingly, the homodyne detection is used to measure the girth variation of PZT. Meanwhile ,the frequency response of PZT can be viewed with the homodyne signal. The results from measuring the PZT pipe show that the method can work well.

The current situation of narrow line-width lasers is briefly introduced. In view of the domestic market dependence on imports of lasers a homebred distributed feedback fiber laser with narrow line-width is realized by developing active phase-shifting fiber grating fabrication technology, solving the sound insulation and vibration isolation package technology, and designing a power amplification optical path of single pump. The prototype power is 35mW, linewidth is less than 3 kHz, relative intensity noise is less than -115 dB/Hz. The main technical indicators are close to advanced foreign products such as NKT and NP. The prototype is applied to the distributed optical fiber sensing system, it can realize good sensing signal demodulation, and the use system is much lower than imported products.

A 168 MHz high repetition all-normal-dispersion mode-locked ring fiber laser is realized experimentally. The wavelength of the fiber laser is 1040 nm and output power is about 270 mW. The output pulses are amplified by using double cladding Yb-doped fiber and the max average output power reaches 12 W. By pumping the high nonlinear photonic crystal fiber (PCF) with the amplified high repetition pulses, the supercontinuum with average power of 9.14 W and spectrum range from 600 nm to 2000 nm are obtained. The mechanism of the supercontinuum generated by amplified pulses is qualitatively explained.

Fe60 alloy coating is fabricated on 45 steel surfaces using mechanical vibration assisted synchronous powder feeding laser cladding process. The microstructure of Fe-based cladding coating and bonding interface, phase composition, element distribution characteristic and diffusion behavior at the interface are investigated by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), respectively. The results show that the bonding interface are complete to cellular dendritic crystal growth, the main phases are composed of (Fe,Cr) solid solution and a small amount of (Fe, Cr) 7C3, Fe2B and Fe0.9Si0.1 compound. Mechanical vibration energy causes dendrite Fe0.9Si0.1 discrete from dendrite internal to interdendrite, and a large amount of (Fe,Cr) solid solution remains in the dendrite internal. Higher mechanical vibration energy leads to better element diffusion in laser molten pool. Meanwhile, the effect of vibration amplitude and frequency on the elements distribution and grain refining at the bonding interface front are also different. Increase the frequency is beneficial to the directional dendrite growth and increase the amplitude is beneficial to the dendritic dispersed distribution at the bonding interface front 40 μm scope. Increase amplitude is more advantageous to the Si and Cr element diffusion at the bonding interface.

To get the accurate measurement of the equation of state (EOS) by using the laser-driven shock wave, it is necessary to guarantee the stability of shock propagation in sample target. Using one dimensional radiation hydrodynamics code MULTI, the stability of the shock wave propagation in planar Al targets driven by the laser power densities of 8.1×1013 W/cm ,with 1.053 μm wavelength, 1ns Gaussian pulse width is studied. The simulation results show that thickness of the substrate should be greater than the shock waves acceleration propagation distance, and the thickness of the sample should be approximately equal to the shock waves stable propagation distance in the design of impedance-match targets, in order to ensure the average velocity of shock waves in the sample approximately equals to the stable transmission velocity.

A high-repetition-rate eye-safe intracavity KTP optical parametric oscillator (KTP-OPO),pumped by an acousto-optically Q-switched Nd:YAG laser,is studied experimentally.The average output power and pulse width of the pump wavelength and the signal wavelength with respect to the repetition rate are analyzed at the same diode pump power. The average output power of 1.6 W and the pulse widh of 6~10 ns at the eye-safe wavelength are obtained with the repetition rate of 5~20 kHz,giving the optical-optical conversion efficiency of about 5.3% from diode power at 808 nm to OPO signal output, and the optical beam quality M2 factor is 5.

A multifunctional narrow-linewidth laser and photonic microwave generation using a monolithic integrated amplified feedback laser under delayed optical feedback is demonstrated. The device can work in signal-mode and dual-mode states by varying the injection currents of laser sections. Photonic microwave is generated by mode-beating of the two laser modes. Through a dual-loop all-optical feedback, the linewidths of both the signal-mode optical signal and photonic microwave signal are reduced by more than three orders of magnitude. Single mode operation with 2.6 kHz linewidth and photonic microwave generation at 37.97 GHz with 1.6 kHz linewidth are experimentally realized.

A passively Q-switched eye-safe intracavity optical parametric oscillator,end-pumped by a pulsed laser diode array,is studied experimentally.The output energy and threshold of the pump wavelength and the signal wavelength with respect to the transmission of output mirror are analyzed at the same Cr4+∶YAG saturable absorber. The output energy of 8.5 mJ and the pulse widh of 2 ns at the eye-safe wavelength are obtained with the repetition rate of 20 Hz, giving the optical-optical conversion efficiency of about 6% from diode power at 808 nm to optical parametric oscillator (OPO) signal output.

Left ventricular assist device (LVAD) is a successful and useful treatment method for end-stage heart failure. An important part-hydrodynamically suspended impeller exposed to corrosive conditions, is required to be sealed hermetically into micro packages. Laser beam welded Ti6Al4V alloy is adopted in anti-corrosion micro packages for the LVAD impeller. Thin and narrow welds are required for such medical equipments. Pulsed Nd∶YAG welding is successfully adopted as sealing method for the impeller. The experimental results show that peak power of 414 W, welding speed of 360 mm·min-1, and overlap of 70% are the final selection of the main laser welding process parameters. Welded joints along the direction of welding line are uniform and stable, the welding line is good, and the heat-affected zone is narrow. There is little difference between welded joints and base metal in terms of mechanical properties. Porosity, inclusions, cracks and other defects are not found.

2198-T851 Aluminum-Lithium alloy is a new high-strength material with low density, high specific strength, good corrosion resistance and well properties in low temperature condition. 2198-T851 with a thickness of 1.8 mm is welded with 2319 filler wire (Al-Cu) by using 6 kW fiber laser on butt welding. The effect of welding parameters on the weld formation and hot cracking are investigated, as well as testing the mechanical properties of the joint and analyzing of fracture morphology.The results indicate that a good joint with well weld formation and no hot cracks is obtained under the appropriate laser power, welding speed and wire feeding rate. The average tensile strength of joint reaches to 272 MPa and the extension rate of joint is 1.6%, the tensile fracture happens in the weld zone with ductile fracture characteristics.

Polypropylene and nylon 66 are used widely and have the connecting needs, but they can not be welded by laser transmission welding because of polar differences and poor compatibility. Given this situation, maleic anhydride is grafted to the side chains of polypropylene to improve the welding performance between polypropylene and nylon 66. The preparation formulation and process of the graft modified polypropylene are introduced, and the mechanical and thermal properties of the graft modified polypropylene are tested. The graft modified polypropylene and nylon 66 are welded by laser transmission welding, which shows that the graft modified polypropylene and nylon 66 have good welding performance. Based on central composite experimental design, through response surface methodology, the mathematical model between laser power, welding speed, fixture pressure and the joint strength are established. At the same time, the interactive influence of welding process is revealed and the optimal process parameters are obtained.

Laser surface melting on ZM61 magnesium alloy is carried out by a continuous CO2 laser under a rapid water-cooling condition. The microstructure and phase constitution of the melted layer are analyzed by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microhardness, and wear resistance and corrosion resistance of the melted layer are tested by Vickers microhardness tester, scratch testing machine and electrochemical workstation, respectively. The results show that the melted layer consists mainly of regular columnar dendrites with a significant fine-grain strengthening effect in the water-cooling condition. The phase constitution is altered by the laser melting process, that is, the substrate is mainly consisted of α-Mg and the interdendritic network intermetallic compound Mg7Zn3 while Mg7Zn3 phase partially decomposed into Mg2Zn3 phase during the laser melting process. In comparison to the substrate, the microhardness of the melted layer is enhanced obviously. The peak hardness of the melted layer is 120.4 HV, which is about twice of that of the substrate. The tribilogical property of the melted specimen is improved with a 59.8% wear mass loss of the substrate.The corrosion resistance of the alloy is slightly decreased with the corrosion potential of the melted layer (-1.4455 V) in comparison to that of the as-received alloy (-1.4262 V).

In order to drill hole on the damping materials of nitrile butadiene rubber, a 1064 nm nanosecond laser is used for relevant experiments. Special state of rubber material in this process is observed, and the changing law of its state under the conditions of different pulse width is investigated and analyzed. The results show that honeycomb ablation state appears on the inside of the hole due to the effect of heat and oxygen erosion in the air. And as a result, the increasing velocity of oxygen diffusing into rubber material, oxidation reaction of the rubber in heat affected zone is aggravated, and oxidative denaturation of rubber is occurred. The diameter and depth of the hole that drilled by laser with shorter pulse width are larger, owing to more powerful shock wave generated by instantaneous higher temperature and higher energy density with time. Under the condition of drilling hole with longer laser pulse width, the energy of laser can be accumulated on the inside of the hole. Ablation of rubber in this area is more serious. For the sake of reducing the influence on the performance of rubber by ablation and aging, pulse width of laser should be as short as possible. At the same time, some auxiliary measures should also be adopted to decrease the area of heat affected zone, such as external cooling, injecting protective gas, and so on.

The effect of heating rate on recrystallization process of laser solid forming (LSF) GH4169 superalloy is investigated by changing the heating rate of the sample during heat treatment. The effect of heating rate on recrystallization nucleation site, recrystallization grain growth rate and recrystallization grain distribution are analyzed experimentally. The results show that the lower residual stress of the inner part of each laser scanning path as the low heating rate can hinder the recrystallization process, so in order to make the sample recrystallization the heating rate must be higher than a critical value. With the increasing of heating rate, the recrystallization nucleation site changes from the only overlapping regions of two adjacent laser scanning paths to both the overlapping regions and the inner regions of laser scanning path, and this is beneficial to the uniform distribution of recrystallization grains. Furthermore, recrystallization grain growth rate increases with heating rate increasing within the parameters used in this experiment.

Optofluidic technique has an important application in cell analysis instrument. In view of the insufficient three-dimensional (3D) focusing ability of the trigeminal type-optofludic, the dynamic analysis of optofluidic with traditional structures is done, some factors affecting the 3D focusing are analyzed, and an efficient 3D focusing micro channel architecture is designed, which is suitable for the optical detection of white blood cells. The structure uses sheath stream flow’s press on both sides to achieve sample stream’s two-dimensional focusing. By adding the sags in the channel, it can achieve the sample stream’s 3D focusing. The focusing areas, velocity distribution and particle trajectory distribution under different kinds of sag are obtained with numerical simulation technique, and the corresponding 3D focusing effect is analyzed comparatively. Result shows that the proposed structure has a better 3D focusing ability and indicates that it will have a good potential application value for the optofluidic chip’s development and application in cytoanalyze.

KDP crystal is grown by the traditional temperature lowering method. From the perspective of orientations, nonlinear refraction and nonlinear absorption for KDP crystal are performed by the single Z-scan method at the wavelength of 532 nm. Based on the application of the KDP crystal, the relationship between nonlinear optical parameters and direction has been proved in the picosecond laser pulse. Under the experimental conditions, it is shown that nonlinear refraction can be clearly observed, but no obvious nonlinear absorption phenomena. Self-focusing effect has been discovered in KDP crystal. Then, nonlinear refractive index γ（n2） and nonlinear susceptibility χ(3)k are calculated through the relative theory. The results show that the nonlinear optical parameters γ（n2）and χ(3)k for KDP crystals can be affected by orientations, and the values are small for phase-matching directions (I and II types).

There are usually large low order aberration in the output beam of high energy laser system. It’s possible to compensate the defocus and astigmatism by a set of spherical concave mirrors and cylinder concave mirrors. According to the cantilever beam theory, a cylinder deformable mirror has been designed. By finite element simulation the structure and size parameters of the deformable mirror are optimized, and the deformation stroke reaches 19 μm, the residual peak to valley value is less than 1.4 μm. A prototype has been produced according to the optimal result. The surface precision and the relationship between deformation and driver voltage are measured by a Fizeau interferometer. The experimental results show that by controlling the displacement of the piezoelectric actuator, this deformable mirror structure can produce the desired parabolic surface, and stroke reachs 11 μm.

In this paper, a CO2 laser (λ1=9.3 μm and λ2=10.6 μm) beam expanding system with high variable expanding ratio is presented. The system lens is designed as a combination of four singlet lenses fabricated with chalcogenide glass material Ge20Sb15Se65, the advantage of the superior property of chalcogenide glasses is molding preparation of surfaces. The laser beam expander is designed as start point of two component zoom design idea, with the specific wavelength, incident diameter, material and other optical parameters on the basic parameters of the ideal target optical system. By using Zemax optical design software, the optical structural parameters of the system are optimized. This optical design of CO2 laser beam expanding system with high variable expanding ratio is good beam collimation, simple structure and also has low cost. The results show that this optical system has a maximum diameter of the incident beam is 6 mm, the bandwidth is 100 nm, variable beam expanding ratio is between 2 to 7 and the maximum wavefront aberration is less than 1/4 of central wavelength. Thus, it can be applied in all kinds of opto-electrical fields.

The output beam of a slab laser is rectangular with high aspect ratio, and its divergence angles in horizontal and vertical directions are quite different. It contains large phase aberrations which greatly limit the beam qualities of slab lasers. A beam shaping and aberration compensation system is designed for a slab laser with the wavelength of 1064 nm in this paper. This system consists of 3 cylindrical and 1 spherical lenses. Cylindrical lenses are able to change the propagation of light in a particular direction, and the combination of two cylindrical lenses with different focal directions can achieve beam shaping in two dimensions. By changing the distance between the lenses, the rectangular beam can be shaped into square collimated beam, whose size varied in the range from 15 mm×15 mm to 19 mm×19 mm with low phase aberrations, while the size of the input beam is 15 mm×1.5 mm.

Small-scale self-focusing is an important factor threating the safe operation of intense laser facility, and estimating the marginal value of small-scale self-focusing in laser beam is an important part of the guidance for the safe operation of intense laser facility. The method of using near-field intensity entropy of the output laser beam to reflect the small-scale self-focusing development in laser beam is proposed. Then the variation regular pattern of near-field intensity entropy with the development of small-scale self-focusing is studied by numerical simulation. Using this regular pattern, an early-warning method is given for the obvious small-scale self-focusing happening in intense laser facility. By contrast with the methods of modulation ratio and contrast ratio, the proposed method offers a more obvious assessment.

It is suggested that the dressed-state electromagnetically induced transparency (EIT) can be used as an efficient way to produce light amplification and quantum noise reduction. The four-level tripod atoms are studied in the scheme by dressed-state atom and collective-mode approach. On two-photon resonance, two strong coherent fields induce the depopulation of a coherent superposition state of two lower states, which leads to quantum beat between the cavity modes. While the two strong coherent fields dress the atoms, the system is simply reduced to a standard EIT model, in which the laser transition, the coherent coupling, and the spontaneous decay constitute a successive population transfer channel to recycle the laser electron. It is for the very mechanism that the cavity modes oscillate with high intensities and exhibit squeezing.

Terahertz (THz) and infrared spectra of four kinds of lactose are studied. THz absorption spectra and the dispersion of refractive index of α-lactose, β-lactose, α-lactose monohydrate, D(+) lactose monohydrate are obtained in the frequency range of 0.2～2.6 THz at room temperature by using of THz time-domain spectroscopy (THz-TDS). The experimental results show that there are the significant absorption peaks for these substances in this frequency range. These absorption peaks show a large difference in the presence or absence of crystallization water for the same lactose. This difference is expected to be used to identify these substances. In addition, the absorption spectrum of four lactose is also measured by the Fourier transform infrared spectroscopy (FTIR) within 1.8 and 10 THz. The spectral characteristics between 0.2 and 10 THz of four lactose are simulated based on the single molecular model by using of Gauss 03 software. Both of simulation and experimental results fit well at the position of absorption peaks. At the same time, the spectral characteristics of four lactose are analyzed based on the density functional theory (DFT). The mechanism of molecular motion shown from the experimental results is presented and analyzed.

Using differential circuit constituted by two photodiodes to detect terahertz (THz) wave is the most basic detection method in THz time-domain spectroscopy system. Before detection of THz wave, the first task is to adjust the quarter-wave plate and make the polarized light beam of equal intensity when femtosecond detection light goes through the Wollaston prism, that is to say that the output differential current of the photodiodes is zero. At present, the most common method of adjusting the quarter-wave plate is manual regulation through the observation with the naked eyes by virtue of the experience of operators, so the regulation accuracy is very low. An autobalance device which can make the s polarized light and p polarized light generated by Wollaston prism have the same intensity is developed. The operational amplifier circuit, voltage conversion circuit and analogue / digital (A/D) conversion circuit are used to process the differential signaling of the two photodiodes, the single chip microcomputer is adopted to control rotation of the quarter-wave plate driven by a stepping motor, and the optical balance can be reached fast. The balance precision of 0.9° can be achieved by the developed autobalance device.

Rare earth-ion doped, disordered laser crystals have attracted a great deal of research interest because of their broad emission spectra and high thermal conductivity. Nd∶BaLaGa3O7 crystal is grown by the Czochralski method. The polarized absorption, emission spectra, and the fluorescence lifetime are measured at room temperature. The bandwidth at 808 nm is found to be 15 nm. The 4F3/2 →4I11/2 luminescence bandwidth and the stimulated emission cross section are 27 nm and 4.24×10-20 cm2 respectively. The 4F3/2 lifetime is calculated to be 311 μs. Disordered crystal Nd∶BaLaGa3O7 is an excellent ultrafast pulse laser gain material, and the spectroscopic characterization will provide a basis for its laser application.

Fourier transform infrared (FTIR) spectroscopy is applied to identify three kinds of different quality Xuanwei hams. A total of 27 samples are tested. The results show that the infrared spectra of the three kinds of different quality Xuanwei hams have more obvious difference. The content of lipid, protein, carbohydrate, aldehyde, alcohol, ketone, ester, hydrocarbon and other compounds in the three kinds of Xuanwei hams changes with the marinating period. The content of lipid and polysaccharide decreases with the growth of the marinating period, while the content of protein increases. FTIR spectroscopy combined with principal component analysis (PCA) is applied to identify 27 Xuanwei ham samples, and the synthetic classification accuracy reaches 100%. It is demonstrated that the FTIR method is a powerful tool to perform component analysis and identification of Xuanwei hams.

The photorefractive index change of iron-doped lithium niobate crystal induced by high power ultrashort pulse laser irradiation is calculated in semi-quantitative and verified in experiment. By theoretical calculations, the refractive index decrease of the iron-doped lithium niobate crystal which is induced by the high power ultrashort pulse laser (0.33 mJ, 10 ps at 527 nm) about 10-4. After the relaxation of a few nanoseconds, the index decrease is reduced to 10-5. In the experiment, the same ultrashort pulse laser is used, which is flattened and its intensity distribution is spatially shaped into a right triangle, to irradiate the iron-doped lithium niobate photorefractive crystal, resulting in rectangular prism, thus 1053 nm signal light pulse through the instantaneous photorefractive prism is deflected. The refractive index decrease calculated according to the angle of deflection is about 10-5 and theoretical result is almost in agreement with experiment. This study suggests that all-optical streak camera using the instantaneous photorefractive effect of iron-doped lithium niobate is expected to achieve the measurement of time characteristics of short pulse.