The method to stabilize the second harmonic generation (SHG) using type Ⅱ phase matching is put forward. The theoretical and numerical analysis has been done. Numerical simulation on type Ⅱ phase matching SHG course in KTP shows that when the fundamental frequency (1ω) light is incident in the SHG crystal deviating the optimal polarizing angle, the second harmonic output (2ω) intensity changes periodically with the length of SHG crystal length increasing. With this kind of periodically changing, when input 1ω intensity fluctuates, the output 2ω intensity curves converge at a certain value of the SHG crystal length. At this point the fluctuation of output 2ω intensity becomes much smaller than that of the input 1ω intensity. With the deviating angle being confined to a certain value, when the input 1ω intensity increases, the required nonlinear crystal length to stabilize 2ω intensity decreases and the energy conversion efficiency does not change. With the input 1ω intensity being confined to a certain value, when the deviating angle increases, the required nonlinear crystal length to stabilize 2ω intensity also decreases and the energy conversion efficiency remains high.

Influence of incoming laser beam and environmental factor on mechanical effect of plasma shock wave was studied. The experiment was performed by focusing output pulses of the Nd:YAG laser at 1.06 μm wavelength with 10 ns pulse width and 320 mJ pulse energy on aluminum targets mounted on a ballistic pendulum. The impulse coupling coefficients Cm was determined as a function of target defocusing distance Z at 1.01×105 Pa. The impulse coupling coefficient increases slowly with the increasing of defocusing distance, and gets maximum quantity at defocusing distance about -12 mm. And then impulse coupling coefficient decreases sharply with the increasing of defocusing distance. The function at 4×103 Pa is similar to it at 1.01×105 Pa, except that the maximum at a larger defocusing distance. The intensity and the diameter of the laser spot are different at the different defocusing distance, so the rarefaction wave effect and the plasma shielding effect are different too. And the mechanical effects of plasma shock wave on target at different defocusing distance are also different. All these factors dominate the influence of defocusing distance on mechanical effect of plasma shock wave induced by laser.

The output capability of large mode area (LMA) multimode fiber laser depends on the fiber bending. To study the relationship, the output capability of multimode fiber laser is measured under various bending diameters, and it also be calculated theoretically. Beam quality factor M2 is measured by the means of knife edge for different bending of LMA fiber and the slope efficiency is measured separately. When bending diameters of 285 mm, 195 mm and 130 mm are used, the corresponding beam quality factors are 2.88, 1.82 and 1.67 with the slope efficiencies of 39%, 35% and 34% respectively. For the LMA multimode fiber used in the experiment, losses of different modes are calculated theoretically under various bending diameters.

Aero-optical aberration wavefront can be represented as a multiplicative summation of the proper orthogonal decomposition (POD) basis functions and time coefficients. So if the basis functions are known, how to obtain the time coefficients real-timely is the key in construction the wavefront. Based on the wavefront′s low order approximation expression, the linear equations set that the time coefficients, basis function′s spatial derivative and the jitters of probe beams are met is established. By solving the linear equations set, the series coefficients are obtained. This approach is applied in the aberration wavefront induced by a heated jet. The results indicate that coefficients obtained by this approach are coincided with those by directed POD analysis of the wavefront time series. The coefficients combined with POD basis functions can reconstruct the wavefront effectively. Because only a few jitters need to be measured among the beam apertures and a few equations need to be solved, so the approach has the potential for real-time coefficients obtaining, sequentially for the fast wavefront reconstruction.

A novel lens arrays optical system with continuously variable focus width from several microns to several millimeters for providing uniform irradiation is proposed, which is composed of two lens arrays and an aspherical lens, and the system converts a circular laser beam into a flat-top square focused spot, which realizes the transformation of beam-shape and the uniform distribution of the spatial intensity at the same time. Based on the adaxial matrix optics and scalar quantity diffraction integral theory, the principle of this system is analyzed, and optimum design of the system parameters and numerical calculations for this system are presented in detail. The simulated results show that the nonuniformity along the x and y direction are ηx=4.6%, ηy=5.3% respectively, the energy efficiency can be up to 95.3%, and by moving the target slightly backward from the focal plane, off-focus length Δz=2 mm is obained, which nearly satisfies the need. The theoretical analysis agrees with the results of the emulational experiment with Zemax optical design software.

In this paper, a novel double Q-switcher structure is designed in order to compensate the thermal induced birefringence in the active medium of 1 kHz laser diode (LD) side-pumped electro-optic Q-switched Nd:YAG laser. The experiment result shows that pulse energy of the double Q-switch Nd:YAG laser is 56% higher than the same situation in single Q-switch uncompensated structure. When the laser output power is up to 450 mJ, pulse energy of 30 mJ is obtained, the extinction ratio of beam is better than 10:1, the pulse duration is about 14 ns, and the optical-to-optical conversion efficiency is 6.7%. At the same time, the novel cavity is modelled and numerically calculating is made by using rate equations, the results are accorded with the experiment.

To get the laser acoustic energy conversion efficiency, TEA-CO2 pulse laser, a spherical piezoelectric ceramic hydrophone and a digital oscilloscope were used to receive, demonstrate and store the optoacoustic signal induced in water. And energy conversion efficiency η was calculated. The results showed that when the laser pulse energy varied below 2 J/cm2, the conversion efficiency η was in the range 10-7～10-5, and increased ten times when the laser beam was focused. If the spectrum width of the laser pulse was fixed, η increased with the pulse energy, on the other hand if the pulse energy was fixed, η decreased when the spectrum width increased. As a result, methods of laser focusing, laser pulse compression and laser energy increasing can be used to enhance the conversion efficiency η, and to get strong thermoelastic optoacoustic signal.

The bistable feature of unabsorbed pump in pump-bypassed Yb-doped fiber (YDF) laser offers a possibility to pump the Er/Yb co-doped fiber (EYDF) in a bifurcated cavity. By this way, the lasing of the second lasing line is in a switching mode with that of 1040 nm lasing line. In this paper the wavelength-switchable lasing of 1040-nm and 1537-nm dual lines is investigated experimentally, and the results suggest that a switchable two-wavelength source could be accomplished efficiently by combining the bistable feature of Yb-doped fiber laser with the hybrid cavity configuration (pump-bypassed cavity plus the bifurcated cavity).

A high Er3+-doped narrow linewidth fiber laser based on fiber Bragg grating (FBG) Fabry-Perot (F-P) cavity was demonstrated. Spatial hole burning effect was restrained by fiber Faraday rotator. Two short FBG F-P cavities were used as narrow bandwidth filters to discriminate and select laser longitudinal modes efficiently. Stable single frequency 1534.83 nm laser was acquired. Pumped by two 976 nm laser diodes (LDs) and two ends output, the fiber laser exhibited 12 mW threshold. Total 39.5 mW output power and one end 22 mW output power were obtained upon the maximum 145 mW pump power. Optical-optical efficiency was 27% and slope efficiency was 29.7%. The output power tended to be saturated when pump power increased. The 3 dB linewidth of laser was less than 7 kHz, measured by the delayed self-heterodyne method with 15 km single mode fiber. The high power narrow linewidth fiber laser can be used in high resolution fiber sensor system.

The origin of lock-in error of the mechanically dithered ring laser gyroscopes (MDRLG) is theoretically analyzed. It is obtained that the lock-in error relates to the input angular velocity, the dither frequency and the dither magnitude. According to the limitation of pulse count decoder caused by the readout circuit, a new method for eliminating the lock-in error of RLG is presented. At first, the phase character at the zero rate of crossing is described by a parabola equation. Secondly, the fractional angular signal that is smaller than a pulse count is compensated. Finally, by utilizing the values of sine, cosine and the second derivate of the phase at the zero rate of crossing, the lock-in error is eliminating. The simulation results show that the maximum output error of RLG is reduced from 6.25% to 0.622%. So this method improves the detection precision of RLG, and the output signal of RLG has preferably stability and repetition.

Based on Possion equation, a thermal model of rectangle end-pumped Nd:GdYVO4 was bulit. The crystal temperature fields of Nd:GdYVO4 were distributed. Then the distortion on pump face was calculated. When the pumping power is 12 W, the radii of pump beam is wp=320 μm, the distortion of Nd:GdYVO4 is 0.855 μm. Based on the previous calculation, the focus of thermal lens changing with input power was calculated. Using ABCD matrix to optimize cavity parameters, V-shaped folded cavity which could compress the laser mode radii on KTP effectively was selected. With the pumped power of 6.71 W, an 1.73 W output power of stable frequency-doubled green light was achieved by V-shaped folded cavity, giving an optical-optical conversion efficiency of 25.8%, and green light non-stability Δ/=1.13%.

The high temperature characteristics of long period fiber grating (LPFG) and its strain characteristics at high-temperature with asymmetric refractive index profile in cross section of fiber induced by high-frequency CO2 laser pulses on common communication fiber (corning SMF-28) were proposed. Experimental results show that the LPFG resonant wavelength shifts linearly when the temperature changes from 200 ℃ to 1000 ℃, and the resonant wavelength shifts linearly with the increase of strain at high-temperature as well. In addition, the measurement sensitivities of strain and temperature were different because the fundamental guided mode was coupled to the different cladding modes.

A scanning fiber probe is developed to perform two-dimensional (2D) scanning for optical coherence tomography (OCT). The probe exploits resonant oscillations of a fiber cantilever, and asymmetry geometrical structure of the fiber cantilever has two distinguished resonant frequencies along orthogonal directions. Orthogonal resonant oscillations are excited simultaneously and 2D scanning patterns are generated when it is actuated by one piece of piezoelectric bimorph through a driving signal with mixed frequencies near above mentioned resonances. The scanning sampling density crucial to imaging quality can be deliberately controlled by setting of the driving frequencies as well as fetching duration. Fine tuning the driving frequencies within the widths of intrinsic resonant curves of the designed fiber cantilever results in large scanning amplitude with different Lissajous trajectories and thus different scanning coverages are produced. For correct image reconstruction, a 2D position sensitive detector is also introduced in the developed probe to record the scanning pattern simultaneously. With the developed probe to the established OCT system, experiments on typical samples for en-face imaging are carried out at 2 frame/s. Those preliminary imaging results are presented in the paper.

Based on the characteristic of semiconductor quantum dots and evanescent wave fiber coupler, a novel fiber amplifier was proposed. This semiconductor quantum dots fiber amplifier (SQDFA) was fabricated by depositing PbS quantum dots prepared by solution route on the fused taper region. Optical amplification was realized by interaction between the signal evanescent field and pump's in the quantum dots. PbS quantum dots were synthesized by simply reverse micelle method. The size of PbS quantum dot was less than 10 nm measured by transmission electron microscope (TEM). The optical gain more than 4 dB was obtained at 1310 nm pumped by semiconductor-laser at 980 nm with 30 mW. The optical gain at 1310 nm shows the spectral blue shift resulted from quantum size effect. This compact quantum dots fiber amplifier has potential applications in high-speed broadband access network.

A new calculation method is proposed for studying the characteristics of liquid crystal spatial light modulator (LC-SLM) when the incident readout light is oblique. The theoretical model is established, and the simulative results are given. According to the relationship of driving voltage to intensity of readout light at normal incidence, rotation angles of LC-SLM molecule with different modulation voltages are deduced and modulation depth is calculated. Phase modulation depth decreases with the incident angle increasing, while phase modulation depth increases with the obliquity of LC-SLM molecule decreasing, i.e., driving voltage of the LC-SLM increases with the intensity of write-in light increasing. With the incident angle increasing, initial phase of readout light decreases, but the maximal initial phase is 0.21π at the incident angle of 10°. The simulative results accord with the experimental data.

It is a higher security technology that the data are encrypted by double-random phase encoding with uniformly distributed random phase.A new encrypted in-line Fresnel holographic mark is proposed based on the double-random phase encoding method, the holography and the digital printing technology. Theoretic and computer simulation prove that the encrypted in-line Fresnel holographic mark has the characteristics of availability and security. Computer simulations also indicate the encrypted in-line Fresnel holographic mark can be compressed with higher compressive ratio. Experimental results on the printing and scanning processes are presented to demonstrate that the proposed encrypted in-line Fresnel holographic mark can be printed on print matter by printer or digital printing machine as an identification mark.

γ-Ni toughened Mo2Ni3Si ternary metal silicide alloy was designed and fabricated by the laser melting deposition process. Differential scanning calorimetry (DSC) and high-temperature microscopic analysis indicated that the Mo2Ni3Si alloy has an eutectic temperature of 1287 ℃ and a liquidus temperature of 1355 ℃. In this paper, the solidification microstructures of γ/Mo2Ni3Si alloy under furnace cooling, water cooling and laser surface remelting conditions were studied. Results showed that under furnace cooling and water cooling conditions, the volume fraction of Mo2Ni3Si primary dendrite and the secondary dendrite arm spacing decreased with increasing cooling rate. However, for the alloy under laser surface remelting condition which had the highest cooling rate (～103 K/s), the volume fraction of Mo2Ni3Si primary dendrite increased markedly to about 62%. Due to its finest structure, the laser surface remelted γ/Mo2Ni3Si alloy possessed the optimum mechanical property (600HV), while many microcracks were observed on the Mo2Ni3Si primary dendrite for the furnace cooled γ/Mo2Ni3Si alloy and its coarse dual-phase structure was much unfavourable to mechanical property.

Laser welding technology and defect of sandwich diamond saw are systemically researched with RofinDC025 laser. The result indicates that a mass of porosities and more Cu are the main welded defect in the welding. The porosities produced by the action together of impurities in the interlayer and powder metallurgy material can be reduced mostly when welding depth is body′s 1/2 in one side and body′s 100% in another side or improving the welding speed. The Cu that produced by the melting Cu plate in the body can be reduced when the lasering lean to the diamond segment. The right welding parameters of 350 mm sandwich saw are that the laser offset is 0～+0.20 mm, in one side the welding line energy is 25～40 J/mm with the laser power under 1000 W, in another side the welding line energy is 80～150 J/mm with the laser power excess 1500 W. Under this optimization condition, the content of Cu is about 0.2%～1.1% in the welded zone, the porosities are less, and the welded blend intensity is up to EN13236 safety standard.

To improve the wear-resisting property of titanium alloy (Ti6Al4V), an experiment of laser cladding (Ti+Al/Ni)/(Cr2O3+CeO2) on titanium alloy by pulsed Nd:YAG laser had been carried out. The microstructure of the clad layer was investigated, and the microhardness was measured. The friction and wear properties of the clad layer were examined in atmosphere. It was found that the microstructures of the clad layer were dispersive undissolved Cr2O3 particles and orbed liquid-precipitated Cr2O3 distributed in the matrixes consisting of fir-tree crystals and eutectics. And a small amount of TiAl ceramic hardening particles was existed. The hardness of the clad zone increased obviously, the maximum was 1150HV, 3～4 times of the substrate. A white narrow metallurgical bonding zone was formatted at interface between the cladding and the substrate, about 10～20 μm. The friction coefficients of the clad layer in dry sliding wear were ranged from 0.2 to 0.3. And the rate of wearing was 4～5 times lower than that of Ti6Al4V alloy guide samples.

The high-speed photography has been employed to realize in situ observation on the formation and evolution of the molten pool in the process of laser rapid forming. The results show that the substrate begins to melt and produce a liquid molten pool with the laser beam scanning on it. After a rather short time (about 1.0 s) the molten pool depth increases to a certain value while the molten pool length fluctuates surrounding an invariableness figure. The depth and width of the molten pool decrease gradually with a constant flow rate powder being fed into the molten pool. And the lifespan of the molten pool turns to be short. Simultaneously the tail of the molten pool runs up that means the thickness of the cladding layer increases continuously with the powder ejecting into the molten pool. The angle between the normal of the free surface of the molten pool and the laser beam axis increases from a few degrees to 20～30 degree. There is an “island heave” emerging and vanishing seasonally at the tail of the molten pool free surface by in situ observation. This is the result of forced convection on the fused liquid of the molten pool induced by surface tension gradient, which has been proved by numerical simulation.

Incoherent radiation of amplifying random media is investigated using Monte Carlo simulation and the characteristics of random laser are observed. The entire emission spectra of random media become narrow abruptly when pumping energies exceed certain threshold values, and when the pumping energies further increase, distinct sharp peaks emerge on spectrum background. The intensity of a certain spatial point within the scattering media is contributed from emissions of many frequencies. And the intensity of single frequency of the entire spectrum is contributed from emissions with wide spatial and angle ranges. It has been pointed out that the incoherent radiation of amplifying random media is essentially different from amplified spontaneous emission without any feedback as well as conventional resonant-feedback laser. The explanation on distinct sharp peaks is that rare photons have experienced rather more scattering events and longer paths in amplifying random media, and these photons accumulate more gain.

In order to provide best parameters for unstable ring resonators with reverse-wave-suppressor (RWS), it is necessary to make numerical simulation. With the help of the self-consistent-equation, Matlab computation results show that RWS can increase the output of forward wave and suppress the reverse wave in unstable ring resonators, by changing the parameters such as the length and magnification of resonator. When forward wave and reverse wave compete for the same particles, which is caused by Doppler frequency shift, suppression ratio of RWS gets high while forward wave output declines. To a certain resonator, a best magnitude can be got to provide the best output amplitude. Results show that introduction of RWS can increase the output of unstable ring resonators. All these computational results are useful for practical unstable ring laser design.

Basing on the dual-wavelength high altitude detecting lidar that we have developed, the daytime observation ability has been realized in its sodium fluorescence channel by employing Na (sodium) atomic optical filter and other relevant technologies. Because of very narrow passband and very high out-of-band suppression of the Na atomic optical filter, the lidar echo at 80～110 km altitude can be obtained even in the noon-time when the background light from the sun is very strong. The ability of 24 hours continuous observation of the lidar system has been demonstrated by the preliminary observation result. This development makes the all time detection and investigation of high altitude atmosphere over our country becoming possible.

In total light scattering particle sizing technique, the calculation of extinction efficiency based on Mie theory can only be applied to the homogeneous spherical particles, what is important is that the Mie theory is expensive in both time and resources. Using the anomalous diffraction approximation (ADA) instead of Mie extinction efficiency can simplify the inversion of particle size distribution. The feasibility and limitations of using the anomalous diffraction approximation for calculating the extinction efficiency of circular cylinder particles are investigated. The genetic algorithm is used to inverse the particle size distribution under the dependent model algorithm. Simulation experiments illustrate that it is feasible to use the anomalous diffraction approximation to inverse the circular cylinder particle size distribution in the total light scattering technique, and the inversion results are steady and reliable. The inversion error is 5.7% when 3% relative error is put in the extinction measurement values. The method has advantages of simplicity, rapidity, and suitability for in-line particle size measurement.

The interaction of laser with solid target material can produce plasma called laser-induced plasma. The counteracting force is generated by the expending of laser-induced plasma. That is the foundation of laser propulsion. The measurement of impulse acting on the targets is very important for the impulse imparting from laser beam to target. A new method is presented by combining pendulum with light-electric tachometer, which is adopted in the experiment for measuring the impulse coupling between laser induced plasma and aluminum target. Considering the structure of measurement equipment and the theory of fluid mechanics, the kinetic equation of the pendulum including air damping term is founded, and target impulse is obtained by using the kinetic equation and the measured pendulum angular velocity. The comparison between experimental results and theoretical results testifies that the difference of the period of the pendulum between experimental measurement and kinetic equation is less than 0.5%. The experimental operation is simple and the experimental accuracy is high.

An optimal design method of parallel plate interferometer is proposed in order to increase the measurement accuracy of angular displacement. The main factors determining the measurement accuracy are respectively discussed based on the analyses of the measurement error of angular displacement. It is noted that the initial angle of incidence on the plane-parallel plate, the index of refraction of the plane-parallel plate and its thickness all have great influences on the measurement accuracy. The research results show that the angular displacement measurement can be realized with higher accuracy by choosing optimal initial angle and component parameters as well as using of a reflecting mirror to amplify the optical path difference.

In the future ultra-span and ultra-capacity optical telecommunication systems, high speed electro-optic polymer modulator is one of the key components, which is an all-fiber component with low insertion loss and high integration. The modulation efficiency can be improved because this kind of modulator can greatly suppress the mode mismatching and operate at much lower modulation voltage. An electro-optic polymer modulator based on the long period grating inscribed in a silica-based optical fiber is modeled as a five-layer uniform circular waveguide, and simulated by using the compact supercell method with the consideration of the complex refractive index of the electrodes. The mode index and mode pattern can be obtained, and can be used to explain some differences of the waveguide properties or the modulator characteristics between with and without the electrodes.

A novel 2×2 optical switch, which consists of phase spatial light modulator (PSLM), polarizing beam-splitter (PBS), mirror, half-wave plate(HWP) and quarter-wave plate (QWP), is proposed. This new kind of configuration of the optical switch has the features of less optical components, compact structure, efficient performance, and insensitiveness to polarization of signal beam. In addition, the straight and the exchange functions of 2×2 optical switch are implemented bi-directionally in free-space. A optical experimental module of polarization-independent 4×4 optical switch is achieved by cascading polarization-independent bidirectional 2×2 optical switch and is analyzed according to path control table. Simultaneously, a kind of polarization-dependent 4×4 optical switch is also investigated for comparison, the exchange sort of the polarization-dependent 4×4 optical switch is achieved by control of polarization state of signal beam for routing.