The geomagnetic field, sodium atomic collision and recoil can affect the number of return photons from sodium laser beacon at the sodium layer in mesosphere. The geomagnetic field can cause Larmor precession of sodium atoms and severely reduce the optical pumping when the long pulse and the continuous wave laser act on sodium atoms. Furthermore, the atomic collision can increase the average return photon flux on a certain extent, while recoil decreases it. In addition, downpumping easily causes optical pumping into transition saturation under lower light intensity. In order to get more return photons, repumping may be used to enhance the average return photon flux. The numerical simulation indicates that the laser with 16% repumping power can excite the number of return photons as 2.33 times of the signal\|frequency (D2a) laser.

Coherent beam combination (CBC) with an all-optical feedback loop is an effective way of scaling power with good beam quality. Our research focused on the technology in theory and experiment, especially on the channel scaling, anti phase perturbation, polarization self-selection, pulsed combination and beam splice of passive CBC with the all-optical feedback loop. The important development is reported, and trends of CBC with an all-optical feedback loop are summarized.

Thulium-doped pulsed fiber lasers have attracted considerable interests as novel laser source, due to their wide applications in eye-safe lidar, laser medical system, optoelectronic countermeasure and special material processing. The research and development on ultrafast thulium-doped fiber laser at 2 μm wavelength are classified, which include the technical approach of the ultrafast thuliun doped pulse output, the novel saturable absorbers of passive mode-locking, the characteristics of thulium-doped passively mode-locked fiber laser output, and the development of high power thulium-doped ultrafast pulse amplifier. Up to now, several main mode-locked techniques, such as actively mode-locking, nonlinear polarization evolution, saturable absorber, and nonlinear amplifier loop mirror have been used to achieve ultrashort laser pulses in thulium-doped fiber lasers. The saturable absorber material mainly include semiconductor, carbon nanotubes, graphene and graphene oxide. The most recent work shows that 80 W average power at 1963 nm has been obtained in a three-stage fiber amplifier with pulse width of 20 ps. The prospect of further development and application of such ultrafast laser sources is discussed in the last part of the article.

Passively Q-switched solid-state lasers with short pulse width, high peak power are widely used in medical applications, optical communications, laser ignition and nonlinear optical conversion for generating new laser sources. Composite laser materials for passively Q-switched laser operation are successfully fabricated with thermal bonding technology and ceramic sintering technology. They alleviate the scattering and reflection loss induced in the surface of separated laser gain medium and saturable absorber, further mitigate the intracavity loss. Besides, composite laser materials eliminate the air gap between gain medium and saturable absorber. So the laser material damage is avoided and stable laser operation is maintained. Based on the potential applications of composite materials for passively Q-switched miniature, high peak power solid-state lasers, the advances and outlooks of passively Q-switched solid-state lasers based on Nd:YAG-Cr4+:YAG and Yb:YAG-Cr4+:YAG composite laser materials are reviewed in this paper.

Gas atomization is characterized by higher sphericity, larger apparent density and better fluidity, suitable for preparing laser cladding special powder. Through the ingredient adjustment of thermal spraying powder Ni60, independently designed supersonic nozzle with confined type is put in use for the atomization, and the atomization experiments are performed under different gas atomization pressures, to obtain the laser cladding alloy powder with excellent performances. The results show that with the gas atomization pressure increasing, the particle mean diameter of powder decreases, as well as the volume mean diameter and Sauter mean diameter. Furthermore, the particle size decreases. In addition, the powder with properties of larger apparent density and better fluidity can be achieved to meet the requirement of laser cladding. But the gas atomization pressure might not increase without limit. The optimum gas atomization pressure is 7 MPa comprehensively, under which the experiments of laser cladding with coaxial feeding are carried on. Compared with the coating by cladding thermal spraying powder Ni60 under the same laser cladding parameters, the coating by the cladding self-designed powder embodies a smoother surface without cracks and pores, and the hardnesses of different coatings are approximately the same.

In situ laser cladding coating with γ′-Ni3Al strengthening phase is fabricated by controlling the Al and Mo contents in Ni-based self-fluxing alloy powder on H13 die steel surface. The microstructure and phase structure of the four kinds of chemical composition powder are analyzed by means of optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The results indicate that the macroscopic morphologies of the four kinds of laser cladding coatings are smooth, dense and without obvious macroscopic defects. Ni-based self-fluxing alloy powder with Al added is easier to generate -Ni3Al phase. When the Al content reaches a certain degree, β-NiAl phase is found in the coating. Fe mainly exists as (Fe, Cr) solid solution, while the (Ni, Cr) phase is small. The β-NiAl phase is almost not found when Mo is added in the coating. When the Al content is small, Mo and Fe combining to form Mo-Fe are intermetallic compound. But when β-NiAl phase is generated in the coating as the Al content increases, Mo and Al combine to form AlMo3. The existence of Mo-Fe intermetallic compound makes (Fe, Cr) solid solution less than that of the same Al content without Mo, but the (Ni, Cr) solid solution is more than without Al. The friction coefficients of all cladding coating samples are lower than the H13 steel substrate. The highest microhardness of the coating increases by 3.3 times and the wear resistance increases by 3.8 times, respectively, in comparison with the substrate.

As one of the ultra-precision machining tools, 157 nm laser is an ideal means of surface micro-machining for hard and brittle materials. By establishing the mathematical model, the effects of the process parameters on the etched surface roughness (Ra) are discussed for laser polishing of materials. The roughness calculation formula is derived by using the least squares method. Experimental studies on polishing micro-processing of LED-GaN semiconductor films have been performed using excimer laser with 157 nm wavelength. Through the comparison of multiple sets of theoretical and experimental roughness values, there is an error between them, but the relative errors are all below 15%, and the smallest relative error is only 4%. For 157 nm laser spanning, the ablated surface with lower roughness can be obtained when the laser repetition rate is lower than 15 Hz and the scanning velocity is higher than 0.7 mm/min. The mathematical model can reasonably explain the groove formation mechanism of the etched GaN surface, which provides a theoretical basis to improve the processing quality.

In order to control the quality of laser milling layer, back propagation (BP) neural network model of the milling laser quality including milling depth and width, and milling layer parameters including laser power, laser velocity and defocus amount is set up. The weight and threshold of the BP neural network is optimized by genetic algorithm (GA), and a quality prediciton model is constructed based on BP neural network. The quality of the laser milling layer is forecasted by the model of GA-BP neural network. The results from BP neural network are compared with that of GA-BP neural network. The results of simulation show that the errors of the two network models are smaller, and the test accuracy are higher. Therefore, the two network models can be used to predict the quality of the laser milling. It is also shown that both the astringent and prediction accuracies of the GA optimized BP neural network are improved.

The simulation of long pulsed laser drilling process is done by using the element birth and death method of ANSYS. According to the recoil force of evaporation on the heated surface, a model of ejection of melted materials is built. After coupled solving the two-dimensional axisymmetric differential equation of heat conduction and one-dimensional Eulerian equation of fluid motion by finite element and finite difference method respectively, the results of temperature field and flow field with temporal variation are obtained. The whole shape of the hole will appear by excluding the expelled element during computation, and the result accords with the experiment in literature. The simulation result explains that the irregular shape at the bottom of the hole and a trumpet shaped entrance appearing in the experiment are induced by the interruption of melted liquid within the thin melted depth and the tension between ejected liquid and melted materials adjacent to entrance， respectively.

Butt welding experiments on 1.5 mm thick TC4 titanium specimen are conducted by using 4 kW fiber laser. The specimen is jointed 0.08 mm aluminum foil in the intermediate layer. The optimal weld shape can be attained by adjusting craft parameters. The shape, metallographic structure, tensile properties and microhardness on welding joint are discussed. It is shown that better welding joint and stronger tensile strength can be achieved by adding aluminum foil in the intermediate layer of TC4 titanium specimen. Microhardness is dramatically stronger in the weld pool with TC4 titanium and aluminum foil than that in the weld pool with only TC4 titanium. The difference is about 90 kg/mm2. In the weld pool with TC4 titanium and aluminum foil, grain is much smaller, and the acicular α′ structure is tiny, and the metallographic structure is in net distribution. Besides, the two kinds of welding joints in the heat-affected zone have almost the same microhardness and microstructure.

A study on transmission laser bonding of silicon and glass by Nd:YAG pulse laser is conducted. Independent and interactive effects of process parameters (power, speed and stand-off distance) on geometric elements of melt pool (melt pool depth, width, and depth/width ratio) are discussed. Based on this, effects of laser energy density on melt pool shaping for transmission laser bonding of silicon and glass are analyzed. And the relationships between energy density and geometric elements of melt pool are quantified. The matching curve of the melt pool depth/width ratio and lap-shear strength is obtained. The results indicate that the melt pool depth/width ratio stays steady when the laser energy density is more than 8 J/mm2, and lap-shear strength achieves the maximum value when the melt pool depth/width ratio is 0.25. Effects of laser energy density on melt pool shaping and bonding quality are significant.

The effect of scanning methods and overlap rate on the temperature field and microstructure evolution of DZ125L super-alloy elementary unit in laser metal direct forming is investigated numerically and experimentally. The results show that temperature field in the molten pool leads to the epitaxial growth of columnar crystal from the substrate; the columnar crystal grows highest at the center position; it is multi-directional crystal at the high part. For double-track forming, the temperature field and the change of microstructure in the overlap zone are strongly influenced by the scanning method and the overlap rate; the back-and-forth scanning method easily leads to the change of the solidified direction; the epitaxial growth of columnar crystal between cladding tracks is obtained when the overlap rate is big enough. The results of calculation agree well with that of experiment.

A 1653 nm Raman fiber amplifier with a narrow line-width output, which adopts the all-fiber configuration is reported. The Raman seeder is a distributed feed back (DFB) diode laser with 8 mW output power and 2 MHz linewidth. The pump source is a 1541 nm Er-doped fiber laser. The Raman gain fiber is 500-m long nonlinear fiber (HNLF). When the pump power is 3.32 W, the output power of the Raman fiber amplifier is 260 mW, corresponding to 15.1 dB gain and 12% slope efficiency. Since the central wavelength of this laser is located at one strong absorption peak of methane molecular, it can be used in many fields, such as the atmosphere monitor and natural gas leak detection system.

In this paper, dual semiconductor saturable absorber mirrors (SESAMs) are utilized to realize stable passively mode locked laser operation, and shorter and more stable picosecond pulses in long time are obtained compared with the case with single-SESAM mode locking. In theory, Haus master equation describing the mode locking dynamics of saturable absorber is numerically solved with split-step-Fourier transform method. The detailed dynamic pulse evolution process with dual-SESAM mode locking is simulated. The relationship between the pulse formation and two SESAM saturable absorption loss parameters q1 and q2 are analyzed. Also the mode locked pulse widths and stability region are calculated, and the numerical results are in agreement with the experimental results well.

A compact and wide-temperature Nd∶YAG laser and grazing-incidence amplifier are reported. Fiber-like Nd∶YAG crystal is used as gain medium and a vertical-cavity surface-emitting laser array(VCSEL) is used for the pump source. Cr4+∶YAG is used for passive Q-switch. In continuous-wave (CW) mode, a maximum output power of 1.808 W is achieved at the highest attainable absorbed pumping power of 5.47 W with an optical-optical conversion efficiency of 33.05% and the slope efficiency of 36.5%. In Q-switched mode, pulse with the shortest pulse width of 7.5 ns, single pulse energy of 87.1 μJ and peak power of 11.6 kW is obtained. Grazing incidence and double-passes amplification of laser with single pulse energy of 81 μJ and pulse width of 13 ns obtained by pulse-pump is investigated. With the maximum pumping power, the pulse energy of 0.88 mJ is obtained with the gain of 10.86 and the energy extraction efficiency of 19.44%. After amplification, beam quality turns into M2x=1.196 and M2y=1.307 from M2x=1.175 and M2y=1.248. This laser system is compact and air-cooled. The fluctuation of output energy is below 3% when the temperature ranges from 15 ℃ to 31 ℃.

The theoretical analysis and experimental research of the optical parametric amplifier (OPA) based on periodically poled MgO:LiNbO3 (PPMgO:CLN) are presented. The quasi-phase-mathed (QPM) wavelength-temperature tuning curves and the curves of average power of each light versus crystal length are simulated, and the influencing factors of optimum length are investigated. When the crystal with grating period of 31.3 μm is operated at 150 ℃ and the OPA stage is pumped by a Q-switched NdYAG laser with average power of 44 W, the input idle power of 4 W at 2.765 μm is amplified by 13.3 W, and the conversion efficiency is 21.14%.

The differences of the maximum output powers and optical-to-optical conversion efficiencies of the intracavity doubling single-frequency Nd:YVO4 lasers pumped by 808 nm and 888 nm laser diodes are compared. The results prove that direct pumping is an efficient method to improve the intracavity doubling laser performance. However, due to the contradiction between the absorbed efficiency and nonradiative transition under 888 nm pumping, the doped concentration of Nd:YVO4 crystal is an important factor for the laser design. By analyzing the influence of Nd3+ doped concentration on the lasing performance in experiment and theory, a Nd:YVO4 crystal with doped concentration of 0.8% (atomic fraction) is chosen as gain medium. At last, a high-power single-frequency 532 nm laser of 21.5 W is obtained from Nd:YVO4 crystal with Nd3+ doped concentration of 0.8% pumped by 888 nm semiconductor laser, and the corresponding optical-to-optical conversion efficiency is 31.6%.

With the rapid development of laser diode and the presence of advanced technology in thermal management and mode control, the average power of solid state laser has already rushed to 100 kW class in recent few years. The characteristics of solid state laser compared with chemical and gas lasers are outlined at first, followed by the detailed examination of several technical approaches which can enable 100 kW laser output, including heat capacity laser, thin disc laser, slab laser systems based on coherent combination, liquid cooling solid state laser(under HELLADS project) and finally fiber laser. After introducing the core concepts and presenting the current research status of these lasers, we conclude by pointing out the secrets behind the good beam quality.

The combination of periodic nonlinear polarization crystal and fiber laser is an effective technological mean to achieve visible and ultraviolet band laser output. In this paper, linearly polarized all-fiber laser oscillator is used as the pumping source, and single-pass, second harmonic generation in 5% (mole fraction) MgO doped periodically poled lithium niobate (PPMgO∶LN) nonlinear crystal is demonstrated. The temperature tuning characteristics are analyzed. Keeping the crystal temperature at 26.9 ℃, the green light output power of 1.437 W is achieved at the pump fundamental power of 8.05 W with the best harmonic efficiency of 17.84%.

A continuous-wave (CW) tunable NdYVO4-PPLN intra-cavity resonance single oscillator (ICSRO) under 880 nm laser diode (LD) resonance pumping is reported. 1.54 W maximum idler output power at 3.66 μm is obtained under the pump power of 21.9 W, corresponding to an optical-optical conversion efficiency of 7.0%. The ICSRO under 880 nm in-band pumping shows significant improvements in threshold, output power, conversion efficiency and power stability compared with that under 808 nm traditional pumping. Since the back-conversion process harms the single resonance oscillator (SRO) down-conversion efficiency under high pump power, the influence of output coupler transmittance on SRO threshold and down-conversion efficiency is investigated. By increasing the output coupling of resonant signal to raise the SRO threshold, the down-conversion efficiency can be maintained under high pump power and efficient signal output can be obtained. 1.54 W idler output and 5.03 W signal output are obtained under the pump power of 21.4 W, corresponding to a total extraction efficiency of 30.2%.

Tunable Tmfiber lasers within a wavelength range around 2 μm have numerous applications such as communications, lidar etc.. In this paper, a high power, widely-tunable Tmfiber master oscillator power amplifier (MOPA) system is reported. The master oscillator is tunable over 160 nm (1921～2084 nm) by use of a diffraction grating, which is placed in the Littrow configuration to provide wavelength selective feedback. The MOPA laser is tunable over 140 nm (1936～2081 nm) and continuous-wave output power higher than 54 W is obtained over a tuning range of 100 nm from 1962 nm to 2066 nm, limited by the seed laser tuning range. The laser yields 77.4 W output power at 1981 nm, corresponding to a slope efficiency of 34.4%.

914 nm wavelength in-band pumping of Nd:YVO4 reduces crystal thermal load and end-surface thermal stress, then the performance of Nd:YVO4 regenerative amplifier is enhanced at high repetition rate. The influence of high-voltage-duration applied to Pockel-cell on Nd:YVO4 regenerative amplifier with output pulse stability of 100 kHz is investigated in detail. When 68 W pumping power at 914 nm center wavelength is absorbed by the Nd:YVO4 crystal and appropriated high-voltage-duration is applied to Pockel-cell, the Nd:YVO4 regenerative amplifier that produces stable 21.2 W average power at 100 kHz repetition rate is seeded by a low power of 1 nJ and 5.7 ps duration semiconductor saturable absorber mirror (SESAM) mode-locked Nd:YVO4 laser with repetition rate of 42.7 MHz.

A tunable all-solid-state Nd:YVO4 ring laser, intra-cavity frequency doubled by a type-Ⅰ matched LBO crystal with 671 nm laser output, is demonstrated in this paper. The laser resonator is designed with a four-mirror ring configuration. The YVO4-Nd:YVO4 composite crystal is end-pumped by a 880 nm laser diode (LD). A Faraday optical diode consisted with TGG rotator and half-wave plate is placed inside the resonator for forcing the laser to operate unidirectionally. A solid Fabry-Perot etalon and a piezoelectric-ceramic are inserted into the cavity for tuning the wavelength. The single-frequency output power of 1.08 W at 671 nm is obtained under the pumping power of 23 W (the absorbed pumping power of 14.5 W), the optical-optical conversion efficiency is about 7.4%. With the etalon tuning, a maximal output power of 738 mW is obtained.

A continous-wave (CW) 500.9 nm laser using intracavity sum-frequency mixing in a doubly resonant configuration is reported. The laser has two sub-cavities. A Nd:YAG crystal and a Nd:YVO4 crystal are pumped by two laser diodes respectively in two sub-cavities. In the two cavities wavelengths of 946 nm from Nd:YAG and 1064 nm from Nd:YVO4 are chosen to be mixed into 500.9 nm laser. A composite Nd:YAG crystal is used to deduce the thermal lens effect under high power pumping, and cavity design is optimized considering the thermal lens effects. Better matching of the modes for the two wavelengths is obtained. In the overlapping of the cavities, sum-frequency mixing is generated with a type-Ⅱ critical phase matching KTP crystal. An output power of 730 mW at 500.9 nm is obtained at the incident pump power of 17.8 W for the Nd:YAG crystal and 10.6 W for the Nd:YVO4 crystal. The analyses and experiment show that the doubly resonant intracavity sum-frequency mixing is a useful method to obtain 500.9 nm laser efficiently.

In order to produce the orthogonally and linearly polarized dual-frequency laser output at 1550 nm, a two-wavelength single-longitudinal-mode erbium-doped fiber (EDF) laser with a structure of compound ring cavity is designed, which employs a polarization-maintaining fiber Bragg grating as the wavelength selector, and uses a saturable absorber of an unpumped EDF as laser single-longitudinal-mode selector. The basic principles of single longitudinal-mode selection of both compound ring cavity and unpumped EDF saturable absorber have been briefly introduced, the effect of the unpumped EDF length on the single-longitudinal-mode selection is theoretically analyzed, and the two-wavelength laser oscillating characteristics are investigated experimentally on different longitudinal-mode selection occasions. The experimental results show that the EDF laser with a compound ring cavity in which both a polarization-maintaining fiber Bragg grating and an unpumped EDF saturable absorber are included can steadily output orthogonally and linearly polarized two-wavelength single-longitudinal-mode laser at 1550 nm, and the wavelength spacing is approximately 0.344 nm. Such a two-wavelength single-longitudinal-mode fiber laser will find wide applications in the fields of laser sensing and measuring system, dense wavelength division multiplexing (DWDM) optical fiber communications, and so on.

A subnanosecond pulsed, one-stage Yb-doped fiber master oscillator power amplifier (MOPA) system for different pumping constructions is reported, which is seeded by a passively Q-switched NdYAG microchip laser. The comparison and discussions of average power, spectrum, together with pulse temporal profile of output laser under the forward pumping and backward pumping conditions are presented. Results show that the latter one provides the better performance, in which average output power as high as 9.3 W is achieved with pulse duration of 450 ps at 10 kHz repetition rate. The corresponding peak power is higher than 2 MW.

A passively Q-switched pulse fiber laser based on graphene saturable absorber is reported. Graphene, polyvinyl alcohol (PVA) with polymethyl methacrylate (PMMA) are mixed as solute and dispersed in the 2-dichlorobenzene (DCB) solvent. The graphene film is on the end face of single mode fiber by using optically driven deposition and introduced in a ring cavity fiber laser as an optically saturable absorber. The stable Q-switched operation is initiated with erbium doped fiber amplifier (EDFA) power of 4 mW. When the central wavelength is 1564 nm, the stable pulse sequence with repetition rate, pulse duration, single pulse energy and pulse peak power continuously switchable with the change of the EDFA power is generated by the passively Q-switched pulse fiber laser. The maximum single pulse energy is 82.4 nJ and the maximum pulse peak power is 25.1 mW at the pulse repetition rate of 28 kHz. Meanwhile, the minimum pulse duration of 3 μs is obtained. This fiber laser also has the ability of long time stable operation.

To further improve the energy transfer efficiency of the semiconductor laser shaping system, a semiconductor laser shaping system based on hyperbola substrate microlens array is proposed. Semiconductor laser beam collimation and splitting can be simultaneously achieved by this microlens array, as a result the number of optical surface is reduced. Slow axis collimated lens of semiconductor laser is designed with the use of telecentric optical path so as to meet the small field requirement of microlens. With the simulation result in ZEMAX, the feasibility of the semiconductor laser shaping system based on hyperbola substrate microlens array is verified. A 30 mm×15 mm irradiance area is obtained with the unhomogeneity of less than 7%, and the energy transfer efficiency of the system reaches 96%.

A numerical model for propagation of optical pulse in fiber is established based on nonlinear Schrdinger equation (NLSE), and the formation mechanisms of self-similar pulse in the oscillator are studied. Self-similar pulse evolution in laser is available under reasonable parameters. The pulse, with strict linear chirp, can be compressed to 90 fs, and its peak power reaches to 26 kW. Pulse width is broadened or compressed along with the different positions of the oscillator. This is because of the interaction of self-phase modulation and group velocity dispersion in fiber. With the increase of net dispersion of the cavity, the output pulse energy increases gradually, while the pulse breathing ratio decreases gradually. Whereas, with the increase of pumping power, both pulse energy and pulse breathing ratio increase. This self-similar pulse can be compressed to near transform-limited with ultra-high peak power.

A compact laser diode side-pumped multipass Nd:YVO4 slab laser amplifier is reported. The master oscillator is a passively Q-switched microchip laser, and the seed laser with average power of 0.5 W and pulse duration of 2.371 ns is obtained in TEM00 mode when the repetition frequency is 20 kHz. In order to achieve high efficiency and high gain amplification output, we design a compact structure to collimate the pump laser and the seed laser. In order to optimize the energy extraction and reduce the thermal aberrations, the pump laser is collimated by a cylindrical microlens in the vertical direction. In order to match the horizontal gain diameter, the spherical lenses (f=75 mm) are used to focus the laser into the slab in the first pass, and the cylindrical lenses (f=60 mm) are used to focus the laser into the slab in the second and the third passes. After three-pass amplification, average output power of 5.5 W, pulse duration of 2.52 ns and M2 of 1.5 are achieved when the repetition frequency is 20 kHz, and the corresponding energy extraction efficiency is greater than 14%.

An all-solid-state continuous-wave (CW) single-frequency 1.34 μm Nd:YVO4 laser is designed and fabricated. Based on a polarized and dual-end pumping scheme, a Nd:YVO4 crystal is directly pumped by an 880 nm laser diode, the 1.06 μm laser is suppressed by the coating of cavity mirrors, and a ring resonator is designed. The measured maximum output power of 9 W at 1.34 μm is obtained with optical-optical conversion efficiency of 18%. The stability of the output power is better than ±1% over a period of 4 h and the frequency shift is less than 8.5 MHz in 1 min. The output beam is almost diffraction limited with a measured beam quality of M2=1.03.

LD pumped Nd:YAG crystal laser emitting at 1356 nm single wavelength from 4F3/2-4I13/2 translation is reported. Continuous-wave (CW) output power of 2.4 W with 1356 nm and 1414 nm dual-wavelength is achieved using flat-flat cavity, and the corresponding optical conversion efficiency is 26.7%. With the insertion of an acousto-optic Q-switcher in the cavity, the loss for 1414 nm increases, so that the 1356 nm CW single wavelength as well as the Q-swithched pulse are achieved. At the pulse repetition frequency of 5 kHz, the pulse width is 71 ns and the peak power is about 3.66 kW.

An intra-cavity frequency doubled Yb:YAG/BIBO 515 nm thin disc laser is demonstrated. The Yb:YAG crystal with 10% doped concentration is 420 μm in thickness and 11 mm in diameter. It is mounted onto the micro-channel copper heat sink by Cr/Au/In.The pump light absorption and pump beam radius are calculated. A four-pass optical coupling system is well designed with two spherical imaging mirrors with diameter of 26 mm and curvature radius of 50 mm. A 3 mm×3 mm×2 mm BIBO crystal cutting at a type-I phase-matching direction of (θ，Φ)=(166.7°，90°) is employed. With 24.9 W incident pumping power, the maximum output power of 680 mW at 515 nm is obtained. The optical-optical conversion efficiency is 2.73%.

The four multi-metal sulfides Cu5FeS4, BaCu2S2, CuGd2S4, and CuAlS2are prepared by ultrasonic atomization and coprecipitation with Fe(NO3)3, Al(NO3)3, Ba(NO3)2, Gd2O3, Cu(NO3)2 and Na2S as raw materials. The phases of multi-metal sulfides are investigated by X-ray powder diffraction. The morphology of the multi-metal sulfides are observed by scanning electron microscope. The absorption and transmittance of the multi-metal sulfides in state of sol from visable light to near infrared wavelength are recorded. The results indicate that the four multi-metal sulfides are of high absorbance for near infrared light, while high transmittance for visible light. It suggests that the nano multi-metal sulfides with such special absorbing characteristics is proposed to be applied in design for novel solar heat shielding.

Tisapphire single crystals are important tunable laser materials. Recent researches are focusing on how to grow large-size and high-quality Tisapphire crystals to meet the demand of high-energy laser development. 30 kg grade Tisapphire of 0.2% ion concentrations has been successfully grown by the Kyropoulos (KY) technique through the optimization of the growth process. The experimental tests show that the crystal has a homogeneous titanium distribution and good optical performance. Meanwhile, the figure of merit (FOM) value of the crystal is larger than 200. The present paper is of great importance for the growth and laser application of large-size Tisapphire crystal.

A new type of neodymium-doped lanthanum fluoride (LaF3Nd) nanoparticles are synthesized by hydrothermal method. It exhibits hexagonal structure and a size of about 25 nm. A series of different concentrations of LaF3Nd nanoparticles dispersion are prepared by ultrasonic technology. The visible-near-infrared spectra show that the dispersion with the optical path of 5 mm and neodymium ion concentration of 1×1020 cm-3 shows high transmittance of 85% at 1053 nm. The lifetime of the La0.95Nd0.05F3 nanoparticles dispersion is 200 μs, compared with that of the powder, it is reduced by 3.8%. These results indicate that the LaF3Nd nanoparticles dispersion with low fluorescence quenching rate, high ion concentration and high transmittance is a kind of promising material used for high repetition rate, high-power and ultra short pulse liquid laser.

Based on the time dependent theory, the random laser emission in two-dimensional disordered medium with different pumping rates and refractive indices is calculated. The spatial distributions of emission spectra and lasing modes are also analyzed. The calculated results show that the larger the difference of refractive index between scattering medium and background medium is, the smaller the lasing threshold is. The emission spectra of different regions are different, and change with the intensity of pump source. The lasing emission is mainly distributed in some certain regions, the pumping efficiency is different for these certain regions, and spatial extent overlap of modes is produced between regions.

AlGaN/AlN/GaN high electron mobility transistors (HEMT) structures with AlN interfacial layer of various thicknesses are grown by metalorganic chemical vaper deposition, and their electrical properties are investigated. The HEMT sample with an AlN layer thickness of about 1.5 nm shows a highly Hall mobility of 1680 cm2/Vs with a low sheet resistance of 310 Ω, and high two-dimensional electron gas (2DEG) density of 1.2×1013 cm-2 are obtained at room temperature, indicating good electrical properties of the HEMT material. Furthermore, the results from atomic force microscopy and high resolution X-ray diffraction measurements confirm that the samples possess well surface morphology and heterostructure interface. Thence, the well heterostructure interface enhances the 2DEG density and mobility of the HEMT materials.

In order to improve particle size inversion accuracy of the dynamic light scattering (DLS), considering non-negative characteristic of the particle size distribution (PSD) and strong anti-noise characteristic of truncated singular value decomposition (TSVD) method, TSVD inversion methods of the trust-region (Trust) and interior point Newton (IPN) non-negative constraints are compared in this paper. Combining characteristics of two methods, a particle size inversion method based on Trust-IPN and TSVD (Trust-IPN-TSVD) is proposed. This method inherits the advantages of the Trust-TSVD and IPN-TSVD methods. The inversion of Trust-TSVD, IPN-TSVD and Trust-IPN-TSVD method for 200~500 nm unimodal distribution particles and 100~700 nm bimodal distribution particles is simulated. Results show that compared with the Trust-TSVD, for unimodal and bimodal distribution particles, Trust-IPN-TSVD can improve the peak value error and the relative error of inversion PSD by 1.68%, 0.2461 and 1.41%, 0.0587, respectively, and its PSD is smoother. Compared IPN-TSVD, for unimodal and bimodal distribution particles, Trust-IPN-TSVD can improve the peak value error and the relative error of inversion PSD by 4.52%, 3.710 and 9.47%, 0.4229, respectively, and its PSD is significantly narrower. Therefore, the inversion PSD of Trust-IPN-TSVD method has higher accuracy and better smoothness, and is more consistent with the theoretical distribution. Finally, the inversion of experimental particles confirms this conclusion.

A frequency mixing method with photon counting level weak local oscillator (LO) and echo signal is put forward to decrease the shot-noise from the strong LO. The receiver is multi-pixel photon counter(MPPC), the central frequency of the mixing signal is 1 MHz, and the optical path differences are 30, 45, 60 m respectively. The experimental analysis shows that power spectral density (PSD) of every data segment has a great number of noise no matter what the distances is. Accordingly, the method of PSD averaging is used to extract the signal from the deep noise, then, matched filtering method is also introduced to enhance the signal-to-noise ratio (SNR). The PSD averaging and matched filtering method are adopted for the frequency mixing signal at the distances of 45 m and 60 m from the signal receiving system, as a result the SNRs are improved by 5.90 and 2.73 times compared with the original PSD signal, and the higher the initial SNR is, the more prominent the improvement of SNR is.

Measuring far-field laser beam profile is an effective way to study the atmospheric transmission effects of high power laser and evaluate the pointing capability of high power laser system in a long distance. A laser beam profiler based on detector array is developed to measure the far-field beam intensity and temporal-spatial distribution of the high-repetition-rate pulsed laser beam, and the image of the far-field beam profile is reconstructed with the bilinear interpolation method. The detector array is composed of 297 Si-PIN photodiode detectors, with the spatial resolution of 1 cm in the central region, an effective sensitive area of 32 cm, and response wavelength between 300 nm and 1100 nm. The beam profiler is capable of measuring far-field beam profile of 1～20 kHz repetition rate pulsed laser, with minimal detectable pulse width of 10 ns, and dynamic range of energy density of 0.02～100 μJ/cm2.

A theoretical model is proposed and a novel system is built for measuring temperature based on the change rule for output power of single-mode-multimode-single-mode (SMS) fiber with temperature. The new measuring system can get the variation of the temperature which has a linear relationship with the output power by measuring the phase change of the output power. The calibration coefficient between the phase and the temperature is 2.5347 for a particular SMS fiber by comparing the two temperature variation. Then, a naturally rapid warming and a linearly slow warming of the temperature are checked by the SMS fiber and a thermometer. It is shown that the error is less than 5%.

An embedded microstructure fiber device with large-core plastic cladding fibers inserted is presented. The refractive index profile of the taper end is uniform, and so is the power distribution. On the basis of the theoretical analysis, the coupling coefficient of the nearest-neighboring fibers is exponentially decreased with the decreasing diameter of the taper. The transmission loss of the device is lower when the length of the taper is longer. This kind of devices are fabricated by the fixed flame method and the movable flame method, respectively. The taper is elongated nearly five times by the movable large-hot-zone fiber-tapering system. The transmission loss of the two devices from one inserted fiber to the taper end is measured with He-Ne laser at about 632.8 nm wavelength. The loss values are about 2.63 dB with the taper length of 0.7 cm and 1.06 dB with the taper length of 3.4 cm. The influence of the taper length agrees with the theoretical analysis, and low-loss device can be achieved by improving the structure.

The absorption characteristics of ytterbium-doped single-cladding fiber are studied experimentally. The effects of pump power, fiber length and seed power on the absorption characteristics are analyzed. The results indicate that, under the situation of absorption saturation, the fiber can resorb 40～60 mW pump power for every 100 mW increase of pump power, and the absorption coefficient tends to a constant with the increase of pump power. The re-absorption capacity and the absorption coefficient of the fiber can be improved with the increase of the fiber length. Besides, it is another way to significantly improve absorption ability of pump light that injecting seed light.

Because of the problem about long burst error which is caused by turbulence in atmospheric optical communication, a scheme of low-density parity-check (LDPC) code with channel interleaving is investigated. Taking the interleaving distance as fitness function, a design method of interleaver based on genetic algorithm is put forward. According to the analysis of the distance property about some interleavers, the new interleaver has obvious advantages compared with the block interleaver,the random interleaver and the chaotic interleaver.The simulation results show that compared with the random interleaver and the chaotic interleaver ,the interleaver based on genetic algorithm at bit error rate (BER) of 10-5 have more gain 0.5 dB and 0.87 dB under weak turbulence, respectively. Above all,the new design scheme of interleaver will have certain utility in atmospheric optical communication.

The distributed optical fiber Raman temperature sensor system (DTS) uses optical fiber Raman scattering effect to measure temperature. However, the spontaneous Raman scattering signals are particularly weak, completely submerge in the noise, and affect the system’s temperature measurement accuracy. To solve this problem, this paper proposes to use wavelet transform, which has been widely used in engineering field, for signal processing. By using Matlab and VC combined programming, wavelet denoising is applied to the system actually. The results show that this method can eliminate signal noise effectively. The average error of the measured temperature is reduced from 3.1 ℃ to 1.1 ℃. And then, both the resolution and precision of the measured temperature of the system are improved.

Side-polished coupling cannot damage the central air hole of capillary optical fiber(COF), so that COF can be conveniently used as atomic guiding or sampling tube. Side-polished coupling of single mode fiber and a novel COF is studied by experiment. And the results prove the coupling method is feasible. By analytical equations, the quantitative relationship between the thickness of the residual cladding and the coupling optical power is calculated. It may be the basis for further study on the side-polished coupling for COFs. Side-polished coupling method also can expand the application of COF or other similar microstructure fiber.

A new kind of dual-core photonic crystal fiber (PCF) polarization splitter based on tellurite glass is designed. The full vector finite element method, coupled-mode theory and the full vector beam propagating method are emplyed to investigate the characteristics of the polarization splitter, meanwhile the quartz glass dual-core PCF polarization splitter with the same structural parameters is applied to compare. Numerical investigations demonstrate that the designed polarization splitter has higher extinction ratio and lower coupling loss. The two polarized lights are separated entirely with 441 μm fiber at the wavelength of 1.55 μm and the extinction ratios in x and y polarization directions are -50.1 dB and -53.6 dB, respectively. When the extinction ratio is less than -20 dB, the bandwidths are 34 nm and 36 nm respectively, and the coupling loss is only 0.0009 dB.

An all-optical signal optimization structure based on the self-phase modulation (SPM) effect of fiber is designed by using two single-mode fiber spans with dispersion compensation, and combining a phase shifter. The self phase modulation effect of fiber is analyzed theoretically. The working principles of optimization structure and all-optical XOR gate based on semiconductor optical amplifier (SOA) and Mach-Zehnder interferometer (MZI) are introduced respectively, and the simulation models of all-optical XOR gate and all-optical signal optimization structure are built by using the optical communication system design software OptiSystem. The all-optical XOR output results at 10 Gb/s and 40 Gb/s rate are optimized respectively, making that the XOR output extinction ratios are improved respectively from 10 dB and 9 dB to about 26 dB, and the eye diagrams with good quality are obtained. The results show that the conventional all-optical XOR output extinction ratio is low generally, the all-optical signal optimization structure can improve the extinction ratio significantly and improve the quality of the output signals.

The diffractive optical element (DOE) is widely used to generate various illumination modes for pupil shaping optics in the projection lithography system. A mixed multi-region design method is proposed to calculate the phase of DOE, aiming at the poor spatial coherence of excimer laser. The DOEs generating conventional, dipole and quadrupole illumination modes are designed and analyzed by both the repeated multi-region design and the mixed multi-region design. Compared with the results of the repeated multi-region design method, the non-uniformities of the mixed multi-region design method can decrease from 26.45% to 1.12%, from 19.93% to 5.45% and from 17.93% to 3.54% respectively for the conventional, dipole and quadrupole illumination modes using the same local optimization algorithm. The analysis results indicate that the DOE designed by the mixed multi-region design can improve the uniformity of the far-field intensity distribution greatly while maintaining a high diffractive efficiency without changing the local optimization algorithm.

Taking advantages of the monochromatic X-ray diffraction property of Laue crystals, an innovative use of logarithmic spiral bent Laue crystals for X-ray monochromatic imaging is investigated. According to the ray tracing method and the surface equation of the logarithmic spiral, the imaging principles and characteristics of the logarithmic spiral bent Laue crystals are studied, including the condition that the diffracted beam can be separated from the transmitted beam, the magnifications and the field of view (FOV). A logarithmic spiral bent quartz (1010) Laue crystal analyzer is developed. With the proposed crystal analyzer, the monochromatic backlight imaging experiment for the mesh grid with a diameter of 50 μm is carried out by taking an X-ray source of Cu target as the backlighter. The experimental results show that the spatial resolution of the analyzer is approximately 11.9 μm under a source diameter of 110 μm. Furthermore, the FOVs of the crystal analyzer are 22.3557 mm and 8.2602 mm in horizontal and vertical directions, respectively.

The identification and measuring method of petroleum pollutant is proposed by three-dimensional fluorescence spectroscopy combined with parallel factor analysis. Different concentration solutions of 97# gasoline, 0# diesel and kerosene in CCl4 are as measuring samples. Every petroleum product as one component is considered as a whole and the specific components are not taken into account. By mixing gasoline and diesel with different concentrations and taking kerosene as interfering substance, the three-dimensional fluorescence spectra of samples are measured with FLS920 fluorescence spectrometer. Instrumental error and effect of scattering are removed and the true spectra are obtained by using excitation and emission correction and blank subtraction. The experiments use the second-order calibration algorithms based on the parallel factor to analyze the spectral data and the second-order advantage is adequately exploited. It is proved that the identification and measurement of different components in mixed sample are achieved accurately in existence of interfering substance and good recovery is obtained.

The pigments on the mural paintings from a Ming Dynasty tomb excavated in Jiyuan City are analyzed by micro-Raman spectroscopy. All the pigments are identified compared with the Raman spectra of standard pigments. The red pigments are identified as cinnabar and haematite, the green pigment as malachite, the black pigment as carbon black and the yellow pigment as yellow ochre. Moreover, the white or grey-white crystal deposits on the mural paintings are also identified by Raman analysis as calcium carbonate in the form of calcite. It is deduced that these crystal deposits originated from the calcium carbonate in the limestone base layer. Driven by the underground water, they penetrated through the pigment layer and re-crystallized on the surface of the mural paintings. The results show that micro-Raman spectroscopy is an effective analytical method for the identification of the pigments and other materials on ancient mural paintings.