By means of analyzing component and source of major contamination in high-power laser facility to investigate impact law on damage resistant ability of large aperture optics surface, clearness control requirement of optics surface in high-power laser facility is obtained. The sampled contamination particles in high-power laser facility are analyzed by scanning electron microcopy. The contamination particles on optics surface are fabricated by natural setting method, damage threshold and law of optics are investigated by Nd∶YAG (SAGA-S). The results show that collected particles are about 20% metallic, 40% organic and 40% mineral, respectively. Both laser cleaning effect and laser induced damage occurrs during the laser irradiation. When the laser energy density is above 10.9 J/cm2 , the particles are removed by the laser energy density. But when the laser energy is above 14.6 J/cm2, damage points occur on the optical surface due to the contamination particle, and the laser induced damage threshold descends with the size of the particle.

By optimizing the pump structure, the axially non-uniform absorption coefficient of YAG crystal is compensated. A 15 mm diameter Nd∶YAG crystal is uniformly pumped. The effect of axially non-uniform absorption coefficient of Nd∶YAG on the uniform pumping is analyzed. Then a new method that can optimize the gain distribution through the modulation of the distance and the central pump wavelength is given. A side-pumped amplifier structure is designed to verify the simulation results by experiment. The scheme used for obtaining uniform gain distribution for Nd∶YAG rod with axially absorption coefficient with range of 2.343~2.882 cm-1 has been proved experimentally.

Research results of microlens beam shaping and homogenizing optical system for the 248 nm excimer laser are reported. Through the actual filming, an excimer laser light energy distribution color image is obtained. Matlab is used to analyze the image and extract relevant information to calculate. Then an actual energy distribution of excimer laser light source is simulated by the optical software ZEMAX. According to the characteristics of the light energy spatial distribution, a microlens beam shaping and homogenizing optical system for the 248 nm excimer laser is designed and fabricated. The experimental results are in good agreement with the theoretical simulations. After the shaping and homogenizing, a high uniform beam spot is obtained finally. The profile of this spot is a standard square with a size of 18 mm × 18 mm. The energy uniformity error (process window) of the beam spot is less than ± 2% , and the top- hat factor of energy distribution is about 0.90. This optical system can transform 85% of the total input beam power into the work plane of output beam. The spot shape of original excimer laser is irregular, and the energy distribution is nonuniform. This technical scheme can be a good solution to these problems. The successful development of this optical system has independent intellectual property rights, and also provides a technical support for the excimer laser micromachining with high quality and efficiency.

Because of multiple scattering, laser beam is diffused and transforms into speckle when propagating through scattering media, such as milk, biological tissue et al. Realization of diffused light into a focal spot by modulating the wavefront of the incident beams is of great significance. In this study, focusing laser beams through opaque scattering media is achieved by introducing the spatial light modulator and continuous sequential feedback algorithm to modulate phase of the incident beam. The maximum enhancement factor of intensity obtained is 50.6139. The influence of the number of square segments of the spatial light modulation and the phase precision of every segment on the enhancement factor of intensity is discussed. Experimental result shows that light intensity at the target area increases with the increasing number of square segments of the spatial light modulation, and becomes stronger with the increasing phase precision.

Using the bichromatic laser whose two frequency components are linearly polarized with the polarization directions orthogonal to each other (lin⊥lin), a better performance coherent population trapping (CPT) based atomic clock can be realized. A laser system is realized, which is a master-slave injection locking configuration with an external-cavity diode laser (ECDL) as the master and a microwave modulated vertical-cavity surface-emitting laser (VCSEL) as the slave by injection locking the + 1st sideband of the output multichromatic laser, and the quasibichromatic laser beam is obtained. The behaviors of the obtained beam and the effects of applying it to generate CPT resonance with atoms are experimentally studied, and some meaningful results provide helpful reference to CPT atomic clock related studies.

To analyze the phenomenon related to the detection of explosives by laser illumination and imaging, theoretical analysis of the process of the laser illumination on the target is carried out firstly. The simulation is implemented with the software ANSYS. Three- dimensional models are built for the study of temperature distribution. A CO2 laser is used with expanded beam to irradiate the target (3 m away), and obtain thermal images (8~14 μm) of the targets with TNT and RDX residues. Studies show due to the effective radiation of explosive and background is determined by the emissivity and reflectivity in 8~14 μm waveband when laser irradiation at a certain power, the explosives and the substrate have significant difference in thermal images. Moreover, irradiation power and time difference may also be important factors affecting the detection.

According to aberration characteristic in length direction of rectangle beam from a master oscillator power-amplifier (MOPA) slab solid system, a new type of wavefront corrector named one-dimension deformable mirror (DM1D) with actuators arranged in one direction is developed. The key parameters such as the thickness of the reflecting mirror, the shape of the cementation face are analyzed and optimized by simulations. The surface of the DM1D is driven by 11 piezoelectric actuators, whose static peak to calley (PV) distance is less than 0.17 mm and which can provide an effective dynamic correcting range more than 5 mm. With activity refrigerating design, the temperature rise of mirror surface can be controled within 1 ℃, which is caused by the input high power laser with the power density of 8 kW/cm2 in long time. The beam quality factor β of the output laser beam can be reduced from 8.82 to 4.38 by DM1D in closed loop experiment, proving that the aberration is effectively compensated. The correcting capability and practicability of the DM1D are verified in more experiments.

Comparative studies on the thermal effect and laser performance of diode-end-pumped Nd∶YAG crystals at 946 nm are presented. The temperature of end surfaces and thermal lensing of crystals are measured. When the absorbed pumping power reaches 10 W, the end surface temperature of the atomic fraction of 1.0% doped composite crystal is 25.9 ℃, which is only 1/3 of that of 1.0% non-composite crystal. Morever, the composite crystal can relieve the thermal lensing effect under the same condition. A compensation of the thermal effects in electro- optical crystals is achieved by employing a quarter-wave plate, which allows for the production of an electro-optically Q-switched 946 nm Nd∶YAG laser at 1 kHz. A maximum output power of 350 mW and 17 ns pulse duration laser is achieved with the atomic fraction of 0.5% doped composite crystal under the incident pumping power of 10.4 W. The power stability is 2.7% . The maximum output power is more than three times higher than that of a noncomposite crystal and two times than that of a atomic fraction of 1.0% doped composite crystal.

Extreme ultraviolet lithography (EUVL) technology that harnesses extreme ultraviolet (EUV) source with wavelength of 13.5 nm can easily break through the technology node of 30 nm thus realize large-scale industrial production. Capillary discharge that directly converts electric power into EUV radiation power of the plasma has a higher conversion efficiency of energy. A coupled EUV source from three plasmas in capillary discharge, by making use of the interaction of the thermal expansion of laser produced plasma (LPP) with the Lorentz force received by three plasmas, produces a larger area of EUV radiation. Therefore, it greatly reduces the repetition rate of capillary discharge under the premise of the requirement for EUV utilization which is favorable for lithography production. On the basis of realizing concurrent discharge of three pairs of electrode and synchronized ignition of discharge with laser, the effect of laser on the coupled source is discussed. It is found from experiment that the positional coupling has so little influence on EUV source that the dynamical coupling caused by LPP becomes the key to the problem to be solved gradually.

Based on the segmentation characteristics in space frequency of wavefront distortion, a new method of constructing wavefront distortion is proposed to study the relationship between wavefront distortion and coherent beam combination (CBC). Taking the structure and parameters of SG- III technical integration line as a model and using Monte-Carlo method to realize the simulation, the effects of low and midhigh frequency wavefront distortions are analyzed. Moreover, the corresponding relationships between the low, mid- high frequency wavefront distortion and the result of CBC are established respectively. The results provide an analysis thought and a theoretical reference of wavefront distortion correction for CBC in highpower laser facilities.

Base on speckle formation mechanism in laser projection display system, two key parameters that influence speckle suppression are theoretically analyzed, namely the number N of statistically independent speckle images and the number M of projection-lens resolution elements within a single imaging-lens resolution element on the screen. The increasing value of the parameter M or N can effectively reduce the contrast of the speckle image. However, although the number N of independent speckle images projected on the screen tends to infinity, the contrast of the speckle image can only be reduced to 1/ M . By using a rotating small diffuser to generate independent speckle image, the degrees of speckle suppression are experimentally compared without projectionlens and with projection-lens in simplified projection system. And the effects of the change of the F-number of the projection-lens or the F-number of the imaging-lens on the parameter M and the speckle suppression are experimentally analyzed. The results demonstrate that for the same value of N and under the same test conditions, the contrast of the speckle image increases from 0.146 to 0.427 and the speckle is more serious due to the presence of the projection-lens, and the increase of the F-numbers of the projection-lens can further deteriorate the speckle image, which will be a challenge for the miniaturization of laser projection system.

Key Laboratory of Film Electronics and Communication Devices. In order to obtain double-pulse with tunable pulse width, a scheme of laser structure based on semiconductor optical amplifier (SOA) is proposed. In this scheme, the SOA is put asymmetric in the nonlinear optical fiber loop mirror, pulse produced by nonlinear polarization rotation of the SOA. when the drive current of the SOA is up to 200 mA, through adjusting the polarization controller, double-pulses with pulse durations of 33.40 ns and 30.08 ns, with frequency repetitions of 10.05 MHz and 12.70 MHz are achieved, respectively. By changing the cavity length of the laser and the position of the SOA in the nonlinear amplifying loop mirror (NALM), double-pulse width changes accordingly due to the switch characteristics of the NALM.

The all-fiber passively mode-locked erbium-doped femtosecond fiber lasers based on semiconductor saturable absorber mirror (SESAM) and graphene oxide saturable absorber mirror (GOSAM) in the same cavity are demonstrated. The fiber ring laser is constituted with 1.4 m Er3+-doped fiber as gain medium, which is pumped by 974 nm diode laser, and with the total cavity length of 12 m. Stable mode-locked laser pulse train occurrs at 29 mW incident pump power by employing GOSAM as the saturable absorber. The pulse width is measured to be 703 fs, and the center wavelength is 1557.67 nm, and 3 dB spectral bandwidth is corresponding to 3.91 nm. However, inserting SESAM with a modulation depth of 18% in the configuration mentioned above, we can obtain ultrashort pulse at 32 mW pump power, and the pulse width decreases to 542 fs. The laser center wavelength and the 3 dB spectral bandwidth are 1561.5 nm and 5.41 nm, respectively. Experimental results show that the novel mode-locking device—graphene oxide has the similiar distinguished saturable absorber ability. With its advantages of low price, simple preparation, it seems to be a good candidate for saturable absorbers in achieving ultrashort pulse operation.

For better understanding the mechanisms of laser cleaning for contamination on surface of stonework, such as black ink and smoked dirt, the cleaning experiments are carried out. Its cleaning thresholds are obtained. Meanwhile, the finite element analysis software is used to calculate the temperature and stress of contamination under laser irradiation. The experimental results are discussed combining the calculation. The evaporation of contamination and thermal stress could be the main causes for removing of the pollutants. The site experiment of laser cleaning of black ink and smoked dirt in Yungang grottoes shows that this technique has a great advantage and can be applied for conservation of stonework.

Directional repair of the same material by laser direct forming is performed on the columnar crystal substrate of DZ125L. Microstructure and normal mechanical properties of cladding layers are analyzed and tested. Besides, the mechanical properties of the interface between cladding layers and directional substrate are tested. The results show that the microstructure of laser direct forming DZ125L is columnar crystal with the primary dendrite arm spacing of 8~12 mm and the deterioration of secondary dendrite arm. The size of columnar crystal after heat treatment rises to 30~90 mm and γ′ strengthening phases separate out on the matrixes of columnar crystals in quantity and uniformly; The longitudinal tensile strength of as-deposited columnar crystal is 1312 MPa, while the elongation is 5.27%. After heat treatment, the longitudinal tensile strength and elongation are 1201 MPa and 6.69%, respectively, which both meet the national standards. The interface between cladding layers and directional substrate shows good mechanical property, which can meet the operation requirements.

To investigate the influences of regular patterns on friction coefficients of wheel-rail contact under mixed lubrication, longitudinal, transverse and rhombus patterns are designed. The film thickness, pressure and contact area ratio are calculated by using deterministic model instead of average flow model. Based on the loadsharing concept, the hydrodynamic film and asperities both contribute to carrying the total load. Therefore the friction force is composed of hydrodynamic friction force and asperity friction force. According to the designed patterns, the surfaces of wheel discs are textured by YAG laser. The friction coefficients are tested on a RSW-2 type wear testing machine and the results are compared with that of the grinded without laser textured. It is shown theoretically and experimentally that the friction coefficient of rhombus pattern is higher than that of longitudinal and transverse patterns. And the friction coefficient of longitudinal pattern is slightly higher than that of transverse pattern. Therefore, laser texturing of the textured surface with rhombus distribution can increase the friction coefficient obviously between wheel and rail under oil-contamination condition.

To improve the wear resistance property and bioactivity of Ti6Al4V alloy which is utilized as implant in medical application, the composite coating of Hydroxyapatite (HA)/TC4 is fabricated on the surface of Ti6Al4V alloy by laser cladding. This process has shown distinctive advantages due to combination the mechanical property of metal substrate and the biological property of ceramic coating. Through optimizing the ratio of HA/TC4 composite and laser cladding parameters, ideal single layer and multiple layer overlapped bioceramic composite coating is fabricated without metallic defects. The composite coating contains phases such as α -Ti, Ti3P, TiO, biocompatible ceramic phases as CaTiO3 and β -Ca3(PO4)2. The width of wear track of composite coating is lower than that of the substrate, which indicate that the wear resistance of Ti6Al4V alloy is significantly improved. The contact angle of simulated body fluid (SBF) against coating is smaller than that against the titanium substrate, which indicate that the wettability is improved by laser cladding coating.

The effect of shielding gas compositions containing various oxygen contents on the weld homogeneity and fluid flow is investigated during CO2 laser and gas metal arc (GMA) hybrid welding process. The results indicate that the shielding gas compositions show significant effect on the homogeneity of weld metal in leading laser. Almost homogeneous distribution of alloying elements can be attained if the oxygen content in the arc shielding gas is more than 2%. In He-Ar shielding, the fluid flow behind keyhole is outward, whereas it is inward as the shielding gas contains greater than or equal to 2% O2. These phenomena are mainly determined by Marangoni flow. The direction of Marangoni flow changes from outward to inward when the oxygen content in the shielding gas is over 2%. It promotes the inward flow of the entire molten pool, resulting in homogeneous distribution of alloying elements in hybrid welds.

The excellent welding joints are obtained when the high strength automobile special steels are welded by CO2 laser. In order to improve the measuring accuracy of the test, the small hole method of measuring residual stress is revised necessarily. The simulation results coincide with the modified test values after ANSYS software being used to calculate residual stress. The influence of line energy on residual stress is researched for laser welding high strength steel plates by the test method. The test results show that the longitudinal residual stress reaches a maximum at a distance of approximately 2.5 mm far away from the center of welding seam，and the farther away from the weld seam, the smaller the value of residual stress is, and the residual stress ultimately achieves stability. The residual stress distribution of the initial stage is close to that of the stable stage by adding the arc plate in front of the welded specimen, which eliminates unstable phenomenon of residual stress of the initial stage. The transverse residual stress increases gradually and the maximum value of the longitudinal residual stress decreases when the line energy increases.

Research on the changes of structure characteristics and optical properties of the port wine stain (PWS) skin after photodynamic therapy (PDT) can evaluate the treatment effect objectively and provide reference for the clinician to adjust the protocol. Based on optical coherence tomography (OCT), the structure characteristics and scattering properties of the PWS skin are measured. Through analyzing the OCT signal characteristics shown in epidermis, dermis and blood, the thickness of epidermis, the diameter and depth of ectatic vessels in the PWS skin before and after PDT are calculated. An optical properties extraction algorithm is developed based on extended Huygens-Fresnel light propagation theorem, to extract the scattering coefficience of the PWS skin before and after PDT. The parameters of 28 PWS patients obtained before and after PDT are compared. The results show that the changes of epidermis thickness and scattering coefficients are not obvious (p>0.05). However, the mean ectatic vessels diameter is decreased and the locations of ectatic vessels in OCT images are deeper than those before PDT (p<0.05). This study indicates that OCT can be used as a noninvasive and in vivo measurement method to evaluate the structure and optical properties of PWS skin. The conclusions imply that this measurement method can be used to evaluate the treatment outcome and adjust PDT protocol individually.

Nano gold refers to the particles with size between 1~100 nm, it can be used to strengthen the light absorption of blood in the process of laser treatment of vascular dermatosis because of its good biological compatibility, structural stability and optical properties. The gold colloid is prepared with sodium citrate as reducing agent. Effect of temperature, reaction time, sodium citrate dose on the size and absorption spectra of gold colloid is studied. Thus the best condition for preparing gold colloid is obtained. After the gold colloid with size of 16 nm is prepared, it is added to blood to study the effect of colloidal gold on the properties of light absorption of blood as a function of temperature. The results show that the absorption of blood increases with the increase of volume ratio. Blood absorption peak values at 545 nm and 581 nm increase by 1.33 times and 1.09 times respectively when the ratio is 5. Under the condition of variable temperatures, colloidal gold does not affect the dynamic absorption characteristics of blood.

For quantitative evaluation problems of the influence of the atmospheric turbulence on offshore laser communication, an approach of measurement of the atmospheric refraction structure constant is proposed based on acquisition and synchronization of 850 nm and 1550 nm band of the laser. Using real-time image processing system field programmable gate array (FPGA) and multi-core digital signal processor (DSP) architecture to realize extraction of target center position and statistics of target gray, the angle of arrival fluctuation variance and the scintillation index are obtained. The dual-band results are calculated by the classic model to obtain the atmospheric structure constant of refractive index and then the obtained results of dual-band under the same condition are compared, and the parameters of the corresponding model are revised, so that the atmospheric refractive index structure constant is calculated to be relatively stable and reliable. Experimental results show that using the improved model to calculate the atmospheric refractive index structure constant, the similarity of results is not less than 80%, and the important parameters can be used as a quantitative assessment of the influence of the atmospheric turbulence on offshore laser communication.

Oxygen absorption rate is the core of passive ranging technology calculation using oxygen A band. In order to ascertain the influence of extreme winter weather on the calculation of oxygen spectral absorption and the accuracy of passive ranging, the passive ranging technology is investigated under the conditions of snowing weather and fog and haze weather. The source is a 1000 W tungsten halogen lamp, and the measuring device is a grating spectrometer with 1 nm resolution. The test data are processed at the range of 550 m. According to the mathematic model of oxygen absorption rate and path length using the correlated-K distribution, the distance is solved by the oxygen absorption rate of tungsten halogen lamp in extreme winter weather. The results indicate that the measurement accuracy of oxygen spectral absorption is affected by extreme winter weather, so the ranging error is great in extreme winter weather; but after removing background, the ranging error is reduced to 8.36% in fog and haze weather and 5.45% in snowing weather. By using background elimination method, the measurement accuracy of oxygen spectral absorption and the ranging precision can be increased in extreme winter weather.

An unobscured reflective optical system with two-mirrors three-reflective is described to reduce off-axis difficulty processing. A piece of aspherical mirrors instead of the primary mirror and third mirror in the traditional off-axis three-reflective system, that is one mirror achieve two mirrors′ responsibility, the complexity of the optical processing is reduced, as well as the difficulty of the alignment. Based on the aberration theory of three reflective system, formula of the coaxial structural is deduced, the equation for the system is obtained as well. The parameters of the unobscured off-axial two-mirrors system are that focal length of 1000 mm, F number is 10, field of view is 2° × 0.4° , and the surface type of the two mirrors are all quadric surface. From the figure of spot digram, modulation transfer function, point spread function and encircled energy, it is observed that image quality is good and energy is more concentrated. The optical system is designed with small volume, simple structure, and light weight.

Optical switch is an important part of a multi-path electronic switch. We propose an optical switch based on a liquid prism. The device consists of a liquid prism and a non-transparent diaphragm with two holes. In initial state, the liquid-liquid surface shows a shape of the positive lens, the incident light can be focused through the liquid cell and then be blocked by the aperture slot. At this time, the device shows light-off state. When a voltage is applied to one side of the liquid prism, the device shows light-on state. Meanwhile, when voltage is applied to both sides of the sidewall electrodes, the liquid-liquid surface presents the shape of a negative lens and the incident light divergence occurs. At this time, the device expresses the both light- on state. Our experiments show that the proposed device has faster response time (rise time: ~85 ms; fall time: ~140 ms) and higher optical attenuation (~965:1) in adaptive liquid optical switches. The device has potential application in light shutters, variable optical attenuators and optical routers.

As a method for light- filtering, acousto- optic tunable filter (AOTF) has wide application prospect. Design and manufacture of high-performance AOTF are key part of this tech. In this work, based on the momentum mismatch, the diffracted efficiency of an AOTF is calculated. Also the relations between momentum mismatch and band-pass and aperture are investigated. The results demonstrated that the tune relation of an AOTF changed with the incident angle of light and the diffracted wavelength is decided by acoustic wave at a fixed incident angle of light. Otherwise, the aperture and band-pass of an AOTF changed with the incident wavelength; we can acquire narrow band-pass and big aperture with a proper incident angle. The theoretical calculations are in agreement with experimental results. This research will be helpful for the design of an AOTF with good performance.

In the field of wireless ultraviolet non- line- of- sight communication, atmospheric scattering and the angle of transceiver are important factors thoes affect the ultraviolet (UV) communication system performance. Based on the single scattering model of UV non- line- of- sight (NLOS) communication, a signal noise ratio (SNR) and channel capacity estimation method of UV NLOS communication is proposed. Then the estimated SNR and quantum- limited SNR as well as their channel capacities are calculated respectively. Comparing between two simulation results, the correctness of the method is verified. In addition, the path loss and channel capacity of UV NLOS communication under different angles of transmitter and receiver are simulated by using computer. Channel capacity under different background noise conditions is also analyzed. The simulation results show that transmitter elevation angle, receiver elevation angle and receiver field of view angle (FOV) have a great influence on the path loss and channel capacity of UV communication. Conversely, transmitter beam divergence angle has little impact on them, and channel capacity decreases as background noise increases.

In high power fiber amplifier which uses large mode area (LMA) fiber, the high-order modes(HOM) appear with the increase of laser output power, and the beam quality degrades severely. The influence of fiber bending on thresholds of HOM is studied in experiments based on the fiber bending loss theory. A ytterbium-doped all- fiber narrow- linewidth and high power master- oscillator power amplifier (MOPA) system is built. Novel watering cooling plates of different sizes are designed and used in the main amplifier stage. By using these plates, a series of optimizing experiments are done with the LMA fiber bending at different radii. The threshold of highorder modes are raised successfully and kW-class nearly single mode laser output is obtained. The beam quality factor (M2) is about 1.4 at 1.31 kW.

A novel high precision fiber Bragg grating (FBG) pressure sensor is proposed. The sensor is based on the structure of elastic diaphragm. The pressure sensing FBG (PS FBG) is connected directly to the diaphragm. Axial displacement occurs under pressure and compresses the PS FBG to realize pressure measurement. The temperature compensating FBG (TC FBG) departs form the diaphragm. So it is insensitive to external pressure. Both FBGs are applied with certain pretensions. Therefore, their response to environmental temperature is nearly the same. Accordingly, real-time temperature compensation can be realized. Without strain delivery among structures, the proposed sensor responses to external pressure immediately and ensures a high precision measurement. In the experiment, the pressure measurement fluctuation of the sensor is less than ±0.7%F.S. during temperature variation. The pressure precision reaches 0.19%F.S. in the rage of 25 MPa.

Coupling efficiency expression of single-mode fiber to single lens and lens array with the same single lens diameter is analyzed under Von Karman turbulence. The structure of small caliber lens array is designed. It is proved that an array with each receiving aperture which is 2 to 3 times of the spatial coherent radius is more suitable for a long distant free space optical communicaton system under strong turbulence and long communication distance, because the system has best coupling effect. It is proved theoretically and experimentally that the coupling efficiency of lens array spatial light is better than that of single lens of equal diameter within sufficient distance.

Through Faraday- effect, dual- polarization fiber grating laser based on magnetic field sensor is demonstrated. However, the sensitivity to magnetic field of such sensor is dependent on the initial beat frequency of the laser. Therefore, the relationship between the beat frequency and the sensitivity of such sensor is studied. Theoretical and experimental results show that the dependence of the sensitivity on the beat frequency is nonlinear. Moreover, the sensitivity increases with the decrease of beat frequency. However, there is an upper limit of this sensitivity which is determined by Verdet constant. By lowering the beat frequency to 2 MHz, the maximum sensitivity about 43 Hz/mT to magnetic field is achieved for a dual- polarization fiber grating laser inscribed on an erbium doped fiber. It also shows that the beat frequency is dependent on the polarization of the 980 nm pump. Therefore, dynamical tuning of the sensitivity optically can be demonstrated by tuning the polarization of the 980 nm pump.

A polarization splitter based on dual-core photonic crystal fiber (PCF) with short-length and ultra-high extinction ratio is proposed, and the coupling property of the dual-core photonic crystal fiber and the performance of the splitter are studied numerically based on full vector finite element method (FEM). It is found that the coupling length of the dual-core PCF can be reduced obviously by enlarging the ellipticity of the hole between the two cores and adjusting the doped index properly, a polarization splitter based on the proposed dual-core PCF with a length of 0.58 mm is achieved that can separate the x polarized light and y polarization lights and the extinction ratio of the splitter can reach 82.33 dB at the wavelength of 1.55 μm. Meanwhile, the bandwidth of extinction ratio more than 20 dB and 10 dB can be as wide as 70 nm and 110 nm, respectively, which covers the C+L wavelength bands. This proposed splitter provides a new structure for designing a splitter with short length, wide bandwidth and high extinction ratio.

TiO2, a kind of inorganic metal oxide semiconductor material, has been widely utilized. It is becoming a research hotspot to improve photocatalytic activity and photoelectric conversion property of TiO2 through incorporation of impurities. The electronic structure and optical properties of N doped, Cu doped and N- Cu co- doped rutile TiO2 are studied by using plane wave pseudopotential method of first- principles based on density functional theory. The results show that with N and Cu co- doped TiO2, new impurity energy levels would be formed in band gap of TiO2 due to the synergistic effect of 2p electrons of N and 3d electrons of Cu. Among them, one of impurity levels is in steady- state, the another level is in metastable state. It is favorable for decreasing the transition energy of electron and effective separation of photoproduced electrons- hole pairs, which largely improve the photocatalytic activity of TiO2. The curve of optical absorption coefficient of N-Cu co-doped TiO2 has larger red shift in the visible region than that of N doped TiO2 and Cu doped TiO2, and the reflectivity of N-Cu co-doped TiO2 also increases.

The slow light propagation in a Ge20Sb15Se65 chalcogenide photonic crystal slab waveguide (PCSW) of air holes is investigated via the three-dimensional plane wave expansion (PWE) method. By perturbing the first two rows of air holes adjacent to the waveguide core, the group index, the bandwidth and the dispersion can be tuned effectively, and the symmetric chalcogenide photonic crystal slab waveguides with zero dispersion are obtained. The slow lights with the group indices of 125, 40, and 18 are demonstrated, with the bandwidths of 1.7, 5.6 and 9.7 nm, respectively. Finally, the effects of refractive index of chalcogenide materials on the slow light in the photonic crystal slab waveguide are discussed. It shows perfect slow-light properties in chalcogenide PCSWs and can be used as an affordable reference for further research in chalcogenide photonic crystal waveguide devices.

A one-dimensional photonic crystal structure including two nonsymmetric magneto-optical (MO) metal defects is proposed to achieve nonreciprocal transmission. The nonsymmetric magnetic microcavities are made of the MO metal defects in photonic crystal. The transmission properties of the structure are studied by the transfer matrix method based on the MO material. The MO effect breaks the time-reversal symmetry while the coupling of two nonsymmetric microcavities breaks the mirror symmetry, which results in nonreciprocal transmission. With the increase of incident angle, the interval of two nonreciprocal tunneling channels increases and reaches its maximum at 50°. When the external magnetic field increases, the interval of two nonreciprocal tunneling channels increases and reaches a maximum at a certain value. The results are demonstrated through an electromagnetic field simulation based on the finite element solver.

Aiming at the problems such as difficult to mearsure and bad consistency of the surfaces in polishing long-focus lens array elements by conventional method, the new way using continuous polishing machine is proposed. According to the theoretical research of the continuous polishing system, the surface of the polishing pad can keep spherical. The workpieces with small curvature spherical surfaces can be polished with the character. The adjusting methods of the polishing pad surface curvature are elaborated. According to the experiments of polishing lens array elements with aperture of 45 mm and curvature radius of 57207 mm in 0.69 m continuous polishing machine, the element surface accuracy and consistency are both better than using conventional oscillating polishing method. At last, the range of the curvature radius that can be polished in the continuous polishing machine is discussed and find that the smaller the polishing pad is, the stronger the ability of polishing spherical surface is. The radius of curvature which is polished in 0.8 m diameter can be as amall as 10 m.

Trapping forces of core-shell particles trapped by Laguerre-Gaussian beams (LGpl beams) are calculated using T-matrix method. The results show that both the maximum of axial and radial trapping efficiencies and trapping regions of optical tweezers increase with the numerical apertures of objective, while the axial and radial trapping efficiencies reduce with too big or too small numerical apertures of objective. The axial and radial trapping efficiencies of optical tweezers increase with the refractive indices of particles cladding, when the refractive indices of particles core are greater than the refractive indices of particles cladding. The axial and radial trapping efficiencies of optical tweezers decrease with the refractive indices of particles cladding, when the refractive indices of particles core are less than the refractive indices of particles cladding. The axial trapping efficiencies increase firstly and then decrease with the azimuthal model index (l) of the LGpl beams. The maximum of axial trapping efficiencies decrease and the curve is parallel to x-axis gradually with the increase of the radial model index (p) of the LGpl beams.

An improved two-step phase-shifting algorithm based on the Gram-Schmidt orthonormalization is proposed. After removing the direct current of the interferograms by a Gaussian high- pass filter and orthonormalizing the intensity of the two-frame filtered interferograms by Gram-Schmidt process, the phase shift can be extracted by an arcsine function according to the relationship between two orthogonal vector norms. In the two-step phase-shifting interferometry, as long as the phase shift value between two-frame interferograms is determined, the measured phase can be retrieved by an arctangent function. This method can not only extract the accurate phase shift value, but also retrieve the phase rapidly. By means of computer simulation and experiment, and comparing the performance of this method with several two-step phase-shifting algorithms, the result proves the effectiveness and the advantage of the proposed method in the phase measurement.

To overcome some drawbacks of splitting-light path (SLP) for plane and concave grating typed spectrometer, including serious aberration, worse spectral fatness and low diffraction efficiency etc, a novel SLP based on volume phase holographic transmission (VPHT) grating is designed. For this grating, its manufacture and theories are investigated, and its diffraction efficiency is numerically simulated. In order to validate this designed SLP, the spectral scaling experiment is performed and the spectral resolution is better than 2 nm, the calibration equation between the scaling wavelength and corresponding pixels is gotten via linear least square fitting algorithm. It is proved that the wavelength absolute value is about 0.37 nm on the wavelength of 635 nm with the method of averaging multiple measurements, the root-mean-square error (RMSE) of full scaling wavelengths is 0.3 nm. In addition, for wavelengths of 200~800 nm, the relationship between wavelength biases and corresponding diffraction wavelengths is established via polynomial fitting algorithm, which can greatly solve the problem of wavelength calibration in SLP.

Wavelength-swept laser is the key component for optical fiber sensing and optical coherence tomography, and its output spectral characteristics determine the resolution of the sensing and imaging systems.An improved heterodyne method and a direct measurement method by fast synchronous time gating with an electro-optic modulator (EOM) are proposed to dynamically measure the output spectra of a selfmade prototype of a ring cavity wavelength swept laser. The spectral linewidth, hence the coherence length of the laser source, are obtained to show its increasing dependence on the wavelength-swept frequency. The linewidth measured by the EOM method is greater than that of the heterodyne method due to the modulation, and the respective linewidth are 37 pm and 4.9 pm while the wavelength-swept frequency is 60 kHz.

The characteristics of underwater ship wake bubbles and interference images under different water conditions by laser with high degree of coherence are studied, and the coherent figures with different depolarization angles are simulated. The simulation model of laser scattering detection by ship wake bubble clusters is based on Monte Carlo method. By the simulation, the intensity of multiple scattering is studied and the distributions of intensity received by forward and backward screens are also given. The Mach-Zehnder experimental platform is set up to detect underwater ship wake bubbles with coherent method in order to verify the veracity of theory and simulation. The results show that it is available to acquire useful forward-scattering information through coherent images. There are great differences among different water conditional coherent images which can be used to distinguish different kinds of water conditions, and further, different sorts of ship wakes. The research offers a new method to judge ship wakes and provides a new idea about ship wake zone detection.

Geiger-mode avalanche photodiodes (G-APD) arrays is being concerned in ultra-weak-light detection. It is necessary to analyze performance of satellite laser ranging system based on G-APDs before engineering application. In this paper, the way of numerical calculation and simulation is used. In the condition of laser echo in the magnitude of single photon and only considering the dark counting noise, although the detect probability and the degree of identifying detection data are low, the effective detection points are enhanced relative to using a single photon detector. As laser echo in multiphoton and only considering the dark counting noise，the use of G-APDs is able to reduce the output of the detector drift. The laser echo is flooded when the detector working in geiger mode because of the strong noise which contains the dark counting noise and day light noise. The flooding effect is restrained by using G-APDs.

In order to improve the resolution of phase modulated surface plasmon resonance (SPR) measurement technology. The signal processing technology is optimized. In the differential phase SPR biosensor based on Mach-Zehnder configuration, the SPR phase can be extracted by comparing the phase difference between the interference signals of p- polarization and the reference signals of s- polarization. The 2- path interference optical signal is recevied by computer. According to the mathematical theory and signal processing knowledge, select and processing the interference optical signals. The phase difference of 2-path signal is analyzed at the same time. In the signal processing technology, the phase difference of ups and downs is 0.006°, and the sensitivity limit is 4.7×10-7 RIU.

With the development of kilo-Herz (kHz) satellite laser ranging technology, high precision and high frequency data of satellite laser ranging is becoming a foundation for the research of satellite spin. Based on Yunnan Observatories kHz satellite laser ranging system, the AJISAI satellite spin is analyzed. Firstly, the original observation data by the orthogonal least square method are proprocessed, and the data of AJISAI using the method of spectrum analysis are studied. Finally, AJISAI satellite corner reflector panel arrangement is combined, AJISAI satellite spin is analyzed, and the satellite spin mean rate is about 0.4382 Hz. This method can be extended to other laser satellite spin determination. At the same time, this method provides a basic condition for building a high precision satellite spin model.

Femtosecond laser induced breakdown spectroscopy (fs-LIBS) is employed to analyze Cu-Al sputtered thin films. The laser induced plasma spectra at different delay time (0~1000 ns) and gate width (100~1000 ns) are obtained. The Stark broadening effects are analyzed for the Al I line at 396.2 nm. Quantitative component analysis for the thin films is carried out with the calibration curve (CC) and the calibration free (CF) method, respectively. The composition difference between the thin films and corresponding targets is compared as well. Additionally, depth profiling is carried out for Al67Cu33 thin films using fs-LIBS combined with a synchronous real-time reflectivity monitoring sub-system. An average ablation depth of 90 nm per pulse is observed at the laser energy of 0.2 mJ.

In order to classify the brands of Chinese liquors effectively, the fluorescence characters of Chinese liquors are compared and analyzed. The concentration scores of training samples and testing samples are obtained by using parallel factor method (PARAFAC) combined with genetic algorithm (GA). Support vector machine (SVM) method is adopted to establish the identification model of Chinese liquors, and the accuracy rate of prediction is 97.5%. The experimental results show that the concentration scores of the three principal components reflect the difference between brands. The combination of PARAFAC and GA provides an accurate method for the rapid identification of unknown samples. The results indicate that PARAFAC-GA-SVM has higher prediction accuracy. The proposed method can effectively extract the spectral characteristics, and also reduce the dimension number of the input variables of SVM. The results can provide a new way for the identification of Chinese liquors.

The laser damage mechanism for thin films on zinc-germanium diphosphide (ZGP) crystal is studied experimentally and theoretically to enhance the laser induced damage threshold (LIDT). ZGP which grows at one time is cut into 6 pieces, and is grinded and polished simultaneously. Four of the samples are coated with antireflection multi-layer optical thin film and are analyzed by scanning electron microscope (SEM), it is found that the thin film is rather smooth while some clusters still exist on some areas of the thin film. Secondary ion mass spectrometer (SIMS) is also used to ascertain that the clusters contain platinum. Laser whose wavelength is 2 μm and pulse width is 31 ns is used to test the thin film on ZGP according to the 1-on-1 method of ISO11254 standard to measure the LIDT of the thin film. The results show that the average LIDT of those coated samples is 0.68 J/cm2. The LIDT is also calculated by finite element method and the result is 3.2 J/cm2. The study shows that platinum impurity has significant impact on the LIDT of optical thin film on ZGP and therefore decreasing the impurity density will increase LIDT of the thin film.