The influence of the structure of microstructure fiber on the spectral broadening of femtosecond laser pulses is experimentally studied. These experiments demonstrate that the spectral broadening of 35-fs pulses of 820-nm Ti∶sapphire laser radiation transmitted through 2-μm core diameter microstructure fibers can be enhanced by a factor of about 1.25 by increasing the air-filling fraction of the fiber cladding from 60% up to 80%, and ultrabroad band continua which are almost 700 nm extending from 520 to 1200 nm and 1000 nm extending from 350 to 1320 nm are respectively generated from these two kinds of fibers. The comparison shows that the efficiency of the nonlinear spectral broadening process can be noticeably improved by increasing the air-filling fraction of the microstructure fiber cladding, due to a higher degree of light localization in the core of such a microstructure fiber.

Novel scheme for all-optical AND gate based on cross-gain modulation in cascaded two stage semiconductor optical amplifiers (SOAs) is presented. Single-port-coupled SOA is exploited in the first stage to improve the output extinction ratio, input power of the second stage is properly controlled, and 2.5 Gbit/s all-optical logic AND operation is demonstrated experimentally. Operation principle is illustrated and experimental results are analyzed in detail. According to the experimental results, the extinction ratio of the output signal from the first stage and the optical power into the second stage are very important to the final results of this logic AND gate. So if these factors are controlled properly, the output performance of the logic AND gate can be effectively improved.

Based on the supercell overlapping method the full vector model was adopted to model polarization properties of elliptical-hole photonic crystal fiber (EHPCF) with central defect hole. It was found that this EHPCF with central defect hole has a larger birefringence and walkoff parameter than the solid core EHPCF does. The dependence of birefringence and walkoff parameter on frequency is different from that of the conventional polarization maintaining fiber. A zero walkoff point occurs at the low frequency region in this photonics crystal fiber (PCF). This offers the possibility that the single mode operates at high birefringence and zero-walkoff at a given wavelength. High birefringence and large walkoff parameter can be obtained by a moderate increase in the central defect hole in the core region and the cladding elliptical hole area and ellipticity.

In this paper, the transversal strain on fiber Bragg grating (FBG) is specially analyzed according to the couple-mode theory. For both cases, plane strain and plane stress, numerical simulation is done for uniform FBG. In the case of plane strain, one peak of the reflection spectrum shifts towards the longer wavelength, while the other shifts slightly towards the shorter wavelength and in the case of plane stress, both peaks shift towards the longer wavelength. Finally, a plan of experiment on FBG under lateral load is designed to examine the conclusions. Good agreements between experimental results and numerical simulations have been obtained. The results of the experiment indicate that the transversal strain is between the case of plane strain and plane stress and more close to the case of plane stress. Since the transversal strain and the axial strain have different contributions to the wavelength shift based on the theoretical analysis, it is possible to obtain the measurement of three-dimensional strain from the Bragg reflection wavelength variation.

An air chamber is introduced which is made of two rectangular prisms. Stability and sensitivity of the chamber are improved using the reflectivity character and senseless to tilting of light beam. Transmission characteristics of light beam are analyzed. Transmission equation of probing light beam and measurement equation of the system at both single-wavelength and dual-wavelength are put forward. The times N of light beam going back and forth in the chamber is determined by distance of between planes of symmetry through respective apexes of the prisms. The sensitivity may be chosen by means of adjusting the distance. The results of experiment indicate that the sensitivity of the photometric sensor is N times that of single-pass cell at lower concentration of material to be measured, and when concentration of material is higher, the sensitivity is proportional to the times of light beam going back and forth at the smaller N, and that the times of light beam going back and forth multiplying action on the sensitivity gets weaker at the greater N. The photometric sensor based on rectangular prism with optical fiber is suitable to measuring trace material.

Applying the antibody of CD34 stained the vascular endothelial cell of periodontal tissue and investigated the effects of He-Ne laser irradiation on the blood vessel remodeling (BVR) of orthodontic periodontal tissue in rabbit. 35 rabbits were divided into normal group and experimental group randomly. All of the tissue sections proceeded with CD34 immunohistochemical staining, measured the microvessel density (MVD) the microvessel area (MVA) of periodontal tissue by computer image analyzing system using SPSS software to proceed with statistic test. MVD and MVA received He-Ne laser irradiation were higher than those of the control side. The differences of MVD, MVA between the irradiated and control side in every experimental group were all significant (P<0.05, P<0.01), except for the 1st day group.

The dynamic micro-deformation of the specimen under laser point source is numerically simulated by MSC.Marc software and measured using laser beam reflex amplifier system. Experimental result and simulation result show that the common action of thermal stress and phase transformation stress makes the specimen deformation. The final deformation direction of the specimen depends on the result of the co-operation of the thermal strain and the phase transformation strain, backwards or towards the laser beam. Compared the experimental with the simulation result, the largest deformation is almost the same and the deformation process is a little different. Considering that there is a kind of un-convention temperature distribution in the limit thickness specimen under laser irradiation, the temperature of inner material is higher than that of the boundary. Wave theory is suggested to modify classical heat transfer model so that simulation precision is improved. The conclusion lays the foundation for further research on mechanism and the process of laser bending.

Hybrid laser-arc welding was used to join AZ31B Mg alloy. Weld penetration, surface formation were researched, and effect of arc stability was investigated in positive and negative welding directions during hybrid welding. The results showed that the weld penetration was increased by more than about one times and the weld stability increased by more than one times, compared the positive direction hybrid welding with gas tungsten arc welding only. It has been proved that the welding for magnesium is a perfect process. For negative direction hybrid welding, welding stable was further improved, but weld penetration was not increased. In addition, arc stability in hybrid welding and arc root location were discussed.

In order to calculate the three-dimensional transient temperature field of the continuous moving laser molten pool, a numeric model is established basing on ANSYS software. In the established model, the influences of the surface temperature of material on laser absorptivity and phase change of material on temperature field of laser molten pool are taken into consideration. The analysis on the time-depended temperature field of laser molten pool is also conducted. During laser processing, the heating and cooling process of laser molten pool can be acquired by the numeric model. The calculated results show that when lasers scanning on the top surface of 45# steel base plate from one point to the another point along straight line, due to thermal conductivity, the temperature of laser molten pool increases with time increasing. The calculated result also indicates that the position of the highest temperature point on the laser molten pool surface is slightly lagged the position of the center point of the laser beam. Under the same laser process parameter conditions, the calculated result agrees with the experimental result, this indicates that the established numeric model is correct and reliable.

Co-base self-fluxing alloy was deposited on helical land as cutting lip of end mill which body was made of 45# steel by laser cladding with synchronous feeder. The effect of laser cladding processing parameters on shape and crack of coating was studied, it showed that width of cladding was decided by the effective size of laser beam, which was depended on the power density and the scanning speed. Height of cladding was decided by the ratio of powder feeding rate to the scanning speed, higher laser power can significant reduce crack, and thin cladding shape was valuable to lower the tendency of cladding crack. The special equipment and processing were researched for laser cladding manufacturing end mill. With optimizing parameters using laser cladding technology, functional layers meeting the specification have been achieved on end milling body made of 45# steel. The coating were with crackless, good shape and satisfying hardness, passed cutting test with GB/T122.4.3-90 standard.

Laser beam welding has gained increasing application in the industry, because of its high ratio of penetration deep to weld width, low heat effects and high welding speed. Keyhole effects are the essential characteristic in laser deep penetration welding. A clear stable keyhole was observed with a high-speed camera in laser welding of GG17 glass. The effects of defocus and welding speed on the size and the appearance of the keyhole and the welding pool were experimentally studied. Under the assumption of the keyhole per thin layer being cylindrical, a heat transfer model was proposed to obtain the temperature distribution and the fluid velocity distribution around the keyhole by a finite element method based on the keyhole observed. Experimental study and simulation show that temperature gradient on the front keyhole wall is steeper than that on the rear, the mass flow rate in the welding pool is about ten times the welding speed, and a new technology for quantitative study of keyhole effects in deep penetration laser welding is developed.

Using frequency-doubled Nd∶YAG laser pumped by laser-diode-array as pump source, a high output power, high conversion efficiency, all-solid-state, quasi-continuous-wave Ti∶sapphire laser system is achieved. The maximum of the Ti∶sapphire laser output power of 4.7 W and the conversion efficiency of 19.6% are obtained at 532-nm pump powr of 24 W. To ensure the ideal broadband output of Ti∶sapphire laser, two sets of Ti∶sapphire resonator mirrors were used, respectively. One is from 750 to 850 nm, the other is from 850 to 950 nm. And the transmissivity is 5%, 10%, 15% respectively for two sets. Because the centric wavelength of the resonator laser is nearly 795 nm, the maximum of the Ti∶sapphire laser output power is 4.7 W with the first set of mirror and the transmissivity of the output mirror is 10%. The second set of mirror can generate the output power of 3 W, which is high enough to achieve broadband tuning for the future.

Through the analysis of the loss and threshold characteristics of a laser diode (LD), the threshold current density of LD with external feedback is calculated, according to the theory of multi-beam interference and the definition of equivalent reflection factor. When the length of external cavity approximates to the wavelength of LD, the obtained equation can be used to analyze the influence of the external cavity to the threshold current accurately. When the length of external cavity is much longer than the wavelength of LD, it is out of work. Because in the experiment the external cavity is much longer than the wavelength, the theory model is simplified by analysis to the injected power. The threshold drive current will be reduced obviously for the external feedback. The theoretical results agree well with the experimental findings.

In this paper a completely new type of solid-state round traveling-wave laser is presented. A Nd∶YAG crystal is used as gain medium. Its resonator consists of only two concave mirrors (one of them is directly coated on the laser crystal surface), between which laser beam travels along a closed 3-dimensional loop. Steady oscillation of many kinds of round traveling-wave lasers has been observed. The laser experiment results indicated that the novel laser has simple structure and stable output. Based on the new structure of the new type of solid-state lasers, high-power high-efficient lasers with high beam quality can be developed by end-pumping at multi-points on the laser crystal. High-efficient single-frequency laser and mode-locked laser with short cavity length can also be developed by means of suitable design.

A novel multi-wavelength erbium-doped fiber ring laser is presented. Mach-Zehnder (M-Z) interferometer is used as comb filter and with an interlevel and composite cavity to selecte the wavelengths. The stable three-wavelength outputs with 0.8-nm wavelength span and 0.1-nm linewidth are obtained at room temperature. Without cooling the gain medium in liquid nitrogen or using gratings and complex, expensive devices, this fiber laser has the advantages of being simple and easily attainable at a low cost.

The variable rotation transformation (VRT) method is proposed to control nonlinear chaos system. Control principle is introduced,and acousto-optical bistable (AOB) system is taken as a typical example to demonstrate the effectiveness of this method. The dynamical behaviors of controlled AOB system are given by computer numerical simulation. The results show that the correlation coefficients cosθ, sinθ are system control parameters, the Lyapunov exponent λ of the system can be changed from the positive numerical value in the chaotic state into the negative numerical value in the periodic state by appropriately selecting correlation coefficients ,and the method not only can control the unstable periodic 2np orbits embedded in initial system to stable periodic orbits, but can control chaos system to other periodic 3mp and 2n×3mp (n,m are integers) orbits.

Optimal crystal length, energy conversion efficiency and pulse width of output signal light of a CsLiB6O12 optical parametric amplifier that is pumped by an ultra-short high power laser with output wavelength of 355 nm and pulse width of 10 ps are theoretically analyzed and numerically simulated. It is presented that CsLiB6O10 crystal optimum length is 27.0 mm in the case of Ip(0)=300 MW/cm2, Is(0)=5 MW/cm2, Ii(0)=0. With increasing the pump power and signal power, CsLiB6O12 crystal length is shorter when it acts as nonlinear crystal of optical parametric amplifier. The signal power output of high conversion efficiency is depended on the optimum crystal lengths, pump intensity and signal power.

Pd(mpo)2 complex is a kind of new functional coordination compound. In order to study the optical nonlinearities of this material, the nonlinear optical absorption and refraction coefficients of Pd(mpo)2 complex were measured by using the Z-scan technique. In the Z-scan measurement, the 7 ns laser pulses at 532 nm wavelength were delivered. The sample is the dimethylformanide (DMF) solution of Pd(mpo)2 with the concentration of 0.75×10-4 mol/L. The results show that the nonlinear absorption coefficient β0=(1.916±0.016) cm/GW and nonlinear refraction coefficient γ0=-(3.153±0.048)×10-5 cm2/GW when incident irradiance is very low, and the nonlinear absorption and refraction coefficients linearly decrease with the irradiance increasing. The nonlinear absorption originates from the near resonant two-photon absorption while the nonlinear refraction is enhanced by near resonant two-photon absorption. The linear dependences of the optical nonlinearities on the incident irradiance arise from the population redistribution due to the near resonant two-photon absorption.

The model of the vertical-cavity surface-emitting laser (VCSEL) is established using SIMULINK and the nonlinear behaviors of VCSEL with multiple external optical feedbacks are studied using this model. For short external cavities, the photon density shows periodic cosine undulation along the external cavity length whose period is equal to half of the lasing wavelength; for relatively long external cavities, VCSEL undergoes the regions of chaos, multiple, double and single period orderly with increasing the length of the external cavity, however, these regions emerge contrarily with increasing the external cavity′s reflectivity. If only the first feedback is taken into account, the nonlinearity is weaker than the multiple feedbacks case due to neglecting the high-order feedbacks that own a lot of energy. It is also shown that the nonlinear behaviors can be constrained by increasing the spontaneous emission factor or decreasing the linewidth broadening factor.

Laser induced damage in optical components is a limiting factor to the improvement of high-power laser. Using K9 glass irradiated with the CO2 continuous-wave laser as an example, the thermal and mechanical damage mechanism of optical material induced by continuous-wave laser is investigated. The equations of heat conduction and thermoelastic dynamics are solved through integral-transform method. Transient distribution of temperature field and thermal stress field is described. It is found that the definition of the thermal diffusion length is not applicable when incident laser is Gaussian beam; therefore, the dependence of the site of the maximal thermal stress on irradiation time is derived by curve fitting method, then the analytical solution of the damage threshold intensity is calculated. Because the stress damage threshold intensity is smaller than the melting damage threshold intensity, permanent damage in optical material is produced when circumference stress exceeds the tensile strength. The damage morphology of K9 glass induced by laser is proved to be cleavage burst. The model exhibits good agreement with the experiment result.

The synthesis and character of novel organic photochromic diarylethenes, 1,2-bis (2-methyl-5-(4-(2-(1,3-dioxacyclohex)benzene)thiophen 3-yl) perfluorocyclopentene (1a) and 1,2-bis(2-methyl-5-(4-benzaldehyde)thiophen 3-yl) perfluorocyclopentene (1a′) are studied. These two diarylethenes are mixed with polymethyl methacrylate (PMMA) respectively to coat the substrates by the spin-coating, and then applied to near-field recording by the solid immerse lens (SIL) as well. The size of recording spot is under 1 μm.

The high average power solid state laser (HAP SSL) crystal Nd3+∶Gd3Ga5O12 (Nd3+∶GGG) has been grown by the Czochralski method. (444) double-crystal rocking curve for Nd3+∶GGG indicates that the crystal has a good quality. The absorption and emission spectra of Nd3+∶GGG crystal at room temperature have been studied. The relationship between the energy level scheme and the emission spectra has been analyzed. The absorption, emission cross-section and fluorescence lifetime have been estimated as 4.32×10-20 cm2, 2.3×10-19 cm2, 240 μs, respectively. The spectroscopic parameters of Nd3+∶GGG and Nd3+∶YAG crystal have been compared, and the Nd3+∶GGG crystal has many advantages over Nd3+∶YAG.

Refractive index and extinction coefficient curves of HfO2, Y2O3, Al2O3 and SiO2 were obtained from their corresponding single-layer thin films. HfO2/SiO2, Y2O3/SiO2 and Al2O3/SiO2 multilayer thin films were deposited by e-beam evaporation. Measurement results show that the experimental reflectances of HfO2/SiO2 and Al2O3/SiO2 agreed very well with the theoretical results, but the experimental result of Y2O3/SiO2 was much lower than the calculated theoretical result which told us that the absorptance performance of Y2O3 relied deeply on the deposition conditions. Deposition environment of Y2O3/SiO2 multilayer may create a large amount of non stoichiometrical Y2O3 which made the absorptance increased abruptly. In addition, absorptances of the fused silica substrate and these multilayer thin films were obtained through calculation.

To improve the laser induced damage thresholds of high power laser films, the effects of directional ion cleaning on the characteristics of substrate surface were investigated. Using End-Hall ion source, K9 glass substrates were cleaned under different cleaning parameters. The re-contaminated phenomenon and ion cleaning effect were verified by optical microscope. The contact angles of substrates before and after ion cleaning were measured using a contact angle analyzer. Atomic force microscopy (AFM) and profile meter were used to measure the substrate pattern and roughness before and after ion cleaning with different parameters, respectively. After ion cleaning, the mechanisms of substrate surface characteristics modification e.g. cleanness, surface energy, contact angle, surface roughness and surface topography were analysed. The investigation shows that directional ion cleaning can remove the re-contaminated impurity, increase the surface energy, control the roughness and pattern of surface, and it is an efficient substrate surface processing method to improve the characteristics of substrate.

In this paper, the principle and experiment of the transient thermal gratings method are introduced. To demonstrate the applicability of the method, the thermal diffusivities of semiconductors, metals, and alloys have been measured by transient reflection grating method. As a result, the measured thermal diffusivities agree well with the values of literatures. In addition, the thermal diffusivities of several alloy samples have been analyzed, which illustrate that different alloy structures have different thermal diffusivity mechanisms. Furthermore, interfacial acoustics wave in the air above the sample′s surface has been observed in the experiments.

A novel long-wavelength InP-based resonant cavity enhanced (RCE) photodetector is introduced. High-reflectivity InP/air gap distributed Bragg reflectors (DBRs) have been fabricated by the selective wet etching of InGaAs sacrificial layers with FeCl3∶H2O solution. And the technique has been successfully applied to the fabrication of long-wavelength InP-based RCE photodetector. Thus the problem, the unachievable epitaxy of high-reflectivity InP/InGaAsP DBR, is resolved. The mesa area of this type RCE photodetector is 50 μm×50 μm, the bottom mirror is 1.5 pairs InP/air gap DBR, the interface reflection of the air and InGaAsP layer serves as the top mirror. The measurement results show that the quantum efficiency of 59% at 1.510 μm wavelength, the dark current of 2 nA at 3 V reverse bias, and the 3 dB bandwidth of 8 GHz have been achieved.

All-fiber wavelength-selective filters are the key components in fiber communication systems, those based on fiber couplers incorporated with Bragg gratings are compact, low insertion loss and low cost. In this paper, the filter based on 244 nm ultraviolet-written Bragg grating in hydrogen-loaded conventional 2×2 3-dB fused coupler is reported. It exists an optimized position and appropriate length of grating to obtain high reflectivity from drop port. The filter with maximum reflectivity about 20 dB, bandwidth larger than 1 nm is obtained. The results are qualitatively analyzed with supermode theory. In order to obtain high drop efficiency, the position of the grating and the speed of the step motor should be carefully controlled.

A theoretical model of wavelength conversion based on cross gain modulation (XGM) in semiconductor optical amplifier (SOA) is derived. Characteristics of extinction ratio (ER) of converted signal under both co- and counter-propagating scheme are discussed in details. It is shown that the ER of output probe would decrease with the increase of the bit rate of signal, and the larger the bit rate of the signal is, the faster the ER of the output probe decreases. The ER attains optimal value when the pump wavelength is equal to the small signal gain peak wavelength. The ER of down wavelength conversion (Δλ<0) is larger in evidence than that of up wavelength conversion (Δλ>0). The ER of output probe would be larger as the increase of ER of input signal. And the ER characteristic of output probe of counter-propagating scheme is better than that of co-propagating scheme under the same condition. Finally, the characteristic difference for two schemes is explained from physical layer.

The autocorrelation function of the output polarization states of the optical transmission links in presence of polarization mode dispersion (PMD) and polarization dependent loss (PDL) was investigated by theory and Monte-Carlo simulation method. An analytical expression for the autocorrelation function was obtained by theory, and it is fit well with the result of the simulation. The results show that the bandwidth of the normalized autocorrelation function increases with increasing the polarization dependent loss, and the bandwidth decreases with increasing the polarization mode dispersion.