The formation and the stability of the sequence of odd and even gap solitons in self-focusing photovoltaic-photorefractive crystals are studied. These gap solitons only exist in semi-infinite gaps, and their existence domain decreases with the increase of their orders. The gap solitons with higher order occupy more lattices. The energy flow value of these gap solitons increases with the increase of propagation constant. Given a propagation constant, gap solitons with higher order have higher energy flow value. For high-order interphase solitons, the intensities of side lobes are larger and the intensities of the middle lobes are the same. The intensities of side and middle lobes can be controlled by changing the propagation constant. The stability of these gap solitons is investigated numerically and they are proved to be stable.

The performance of the mixed radio frequency/free-space optical (RF/FSO) systems is presented based on decoding and forward relaying. A mixed RF/laser communication system model is constructed with subcarrier multilevel phase shift keying modulation. The exponentiated Weibull atmospheric turbulence channel with pointing error effect is adopted for FSO communication link and the RF link undergoes the Nakagami-m fading channel. We derive the analytical expressions for cumulative distribution function of equivalent signal-to-noise ratio. The novel mathematical presentations of outage probability and average bit-error-rate are developed based on the Meijer′s G function. The outage probability and the bit-error-rate are compared for different turbulence intensities and receiving apertures. The simulation results show that the pointing error has less effect on the outage in moderate atmospheric turbulence than in weak turbulence, the aperture averaging effect improves performance of the mixed RF/FSO communication system effectively, and the FSO channel is dominant in the mixed system.

A line beam shaping system is developed for low temperature poly-silicon preparation with excimer laser. A spot conversion module is installed to make the beam cross sections of horizontal axis and vertical axis exchange their position. A beam expanding module is used for collimating the short axis of the initial beam, and its magnification determines the spot size of the short axis to match the aperture of the short axis beam homogenizer. The beam homogenizers for long and short axes based on lens array are used to improve the homogeneity of the spot energy distribution and restrict the spot size. A projector is installed to project the beam to the work piece. In order to realize precision positioning of the optical elements, a mechanical adjusting structure is designed and manufactured. The effects of the center error of the lens array unit and the deviation of the working plane on the line beam quality are discussed based on the simulation. The line beam shaping system is used for shaping a homemade high-power excimer laser, and the results show that the measured energy transfer efficiency of the system is 33%, the spot size on the work piece is 100 mm×0.3 mm with the average energy density of 470 mJ·cm-2, and the energy distribution homogeneity of long axis is 93.95%. These results can meet the requirement of annealing technology.

Aiming at the resource consumption of the virtual network mapping in the elastic optical network, we propose a node-first virtual network mapping algorithm considering the influences of the node and the link on resource requirements of virtual network mapping. Virtual nodes are firstly sorted according to the node weight and physical nodes which meet the resource requirements are then allocated for virtual nodes by the greedy principle. Finally, the virtual links are mapped to the shortest non-loop physical path by coordinated mapping. Simulation results show that the proposed algorithm can reduce resource consumption of virtual networks and the blocking probability of network request.

To achieve spectral combining of multiple-wavelength beam array based on reflective diffraction grating, a home-made reflective diffraction grating coated with gold film is used as a dispersion element to achieve spectral combining of two single-mode laser beams with wavelength of 1064 nm and 1080 nm. The structure of the combination system and the optimization method for the beam quality are studied. The combined power of 13.64 W, combined efficiency of 91.9% and combined beam quality of 1.53 are achieved. The beam quality degradation and its influence factors in dispersion plane are estimated.

Based on the coupled higher-order nonlinear Schrdinger equation with varying coefficient, evolution characteristics of optical soliton and Airy pulse with initial chirp transmitting in the anomalous dispersion region of the inhomogeneous optical fiber are studied by the split-step Fourier method. The results indicate that the Airy pulse can produce trapped solitons in positive and negative chirp conditions. When the initial chirp is positive, a new Airy pulse whose propagation direction is opposite to the original acceleration direction is generated. When the initial chirp is negative, the Airy pulse is dispersed in the direction opposite to the accelerating direction. The transmission characteristics of the Airy pulse with initial positive chirp are investigated under different truncation coefficients and nonlinear conditions.

In order to solve the problem of frequency identification of the low frequency water surface acoustic wave (WSAW), a laser interferometric detection method is proposed based on an improved phase-generated carrier wave (PGC) demodulation technique. A simple laser interferometer system is used to detect the low frequency WSAW caused by underwater acoustic sources. Frequency mixing of four carrier signals is conducted and two orthogonal interference signals are selected by power comparison. Further phase demodulation and spectrum analysis are carried out, and the frequency measurement for WSAW is achieved. Simulations and experiments for low frequency WSAW are conducted to confirm that the improved PGC demodulation method can effectively avoid orthogonal signal blanking when the initial phase of carrier signal is uncontrollable. The accurate frequency identification for WSAW can be achieved, and the frequency detection limit is as low as 30 Hz. Good detection effect for WSAM with low frequency can be achieved by the proposed method under conditions of frequency-varying WSAM and low-frequency WSAM with large-scale disturbance wave interference. The results show that the improved PGC demodulation method can accurately determine the frequency of WSAW and be able to resist disturbance.

In order to reduce the waiting time and buffer resource consumption of conventional automatic repeat request technology, make the redundant symbol number of digital fountain codes adapt to the varying of channels, and guarantee the quality of the free-space optical communication at the same time, a Q-learning-based Raptor10 code decoding strategy is proposed. Reducing redundant symbols and decoding bit error rate are as the joint return target in the proposed strategy, and Raptor10 code redundant symbols received by receiver are dynamically adapted. As the decoding experience is accumulated continually, the communication performance is improved automatically. Simulation results show that, under the weak, moderate and strong turbulence conditions, the proposed strategy reduces 3% average redundant symbols compared with conventional Raptor10 codes with fixed redundancy rate and linear filtering adaption algorithm.

The noise of fine tracking detectors in acquisition, tracking and pointing systems is different, which has different influences on the position location of light spots. The source of the strip noise of detectors is analyzed, and the influence of the strip noise on centroid algorithm is deduced theoretically. The threshold centroid algorithm is used to locate the light spots of images with stripe noise and salt and pepper noise, and location deviations of X axis and Y axis corresponding to different signal-to-noise ratios and different threshold values are simulated, and the light spot location accuracies of X axis and Y axis are compared. The simulation results show that the light spot location accuracy of X axis is better than that of Y axis when the stripe noise exists in Y axis direction. The tracking accuracies of X axis and Y axis of the fine tracking system under different system configurations and different interference amplitudes are experimentally tested. It proves that, for fine tracking system with two symmetrical orthogonal axes, the tracking accuracy of X axis is better than that of Y axis, which verifies that the location accuracy of X axis is better than that of Y axis when the stripe noise exists. The results obtained from simulation and experiment are identical.

Aimming at the space laser communication system requirement of miniaturization, a scheme of using the avalanche photo diode (APD) type four-quadrant detector to complete the tracking and communication is proposed. This communication system could effectively reduce the volume and power consumption and improve the light energy utilization. The overall scheme of composition and working principle are introduced, the experiment is established in laboratory, and the detection performance which includes data collection, communications rate, limiting sensibility, tracking accuracy is tested. Experimental results show that by use of the APD type InGaAs four-quadrant detector with photosensitive surface diameter of 4 mm, the communication rate is 10 Mb/s, the detection sensitivity is -35.4 dBm and the bit error rate is 10-6 under conditions of Manchester code, intensity modulation/direct detection. The minimum position resolution of the spot position detection is 2 μm, the detecting range of QD is about 0.8 mm, and the angular resolution is 0.8 μrad while the diameter of light spot is about half of the diameter of the photosensitive surface.The feasibility of using the APD type four-quadrant detector for simultaneous tracking and communication is demonstrated, which provides technical support for design of the whole space laser communication system requirement of miniaturization.

The frequency and intensity noise of the probe laser in the integrating sphere cold atom clock (ISCAC) are studied theoretically and experimentally. The power spectral density of the relative intensity noise of the probe laser in the high frequency region (0.1-10 kHz) is maximally compressed by 15 dB with the methods of stabilization of laser power and the removal of stray light, and simultaneously the influence of the probe laser frequency noise on the ISCAC frequency stability is decreased to 9τ－1/2×10－15 where τ is the integration time.The theoretical analysis results show that, up to now, the influence of the probe laser frequency noise on the ISCAC frequency stability is 2.5τ－1/2×10－13. Thus a scheme to reduce the influence of the probe laser frequency noise is proposed, that is, the detection time is increased appropriately in a certain clock cycle. With this method, the influence of the probe laser frequency noise on the ISCAC frequency stability can be reduced to 9.4τ－1/2×10－14.

The electromagnetically induced grating (EIG) effect is theoretically studied under the cold atomic and room-temperature atomic systems, respectively. The study results show that the first-order diffraction efficiencies in the cold atomic system and the room-temperature atomic system can reach 32.5% and 30%, respectively. The two diffraction efficiencies are very close to the ideal diffraction efficiency of a sinusoidal grating. However, as far as the actual condition is concerned, the preparation of a cold atom system is more difficult than that of a room-temperature atomic system. Moreover, the cold atomic system is more complex and requires higher experimental conditions.Therefore, the realization of EIG with room-temperature atoms is more superior. The theoretical studies also indicate that the EIG effect can also occur with low-power signal and low-power probe beams, and the first-order diffraction efficiency is close to the theoretical maximum, which can be used to realize a weak field modulation with another weak field.

The beam quality (M2) factor measurement requires the collimation of the optical path and the reduction of the influence of noise on the measurement of spot radius. Deviation of the optical path results in the deviation of the captured spot from the center of CCD, and the measurement values of spot radius and M2 factor will have extra error caused by noise. Aiming at the condition of containing noise and optical path deviating from the center of CCD, a modified method for M2 factor measurement is proposed. The proposed method can collect two spots at positions in optical path with different offsets when the optical path is not straight. The true value of spot radius can be obtained correctly, and then the M2 factor without collimation error can be obtained. The relationship among the spot radius of laser beam, the M2 factor and offset is deduced theoretically. Numerical simulation and experiments are carried out to study the relationship among the spot radius, M2 factor and offset. Consistent results are obtained, which proves the reliability of the proposed method.

In a scanning beam interference lithography (SBIL) system, the exposure spot size has significant influence on the stitching accuracy of interference fringes, efficiency of grating fabrication and quality of interference field. In order to obtain a reasonable exposure spot size, the influence of exposure spot size on nonlinear error of interference fringe, line stitching error and exposure contrast is discussed by numerical simulation based on the transmission law of Gaussian beam and scanning stitching mathematical model. Results show that, compared with the large-sized spot, the small exposure spot is more conducive to controlling nonlinear error of interference fringe. Because there exists periodic measurement error, a small exposure spot helps to reduce the line error after stitching and enhance the exposure contrast. The exposure optical path of SBIL system is designed and optimized. The left and right spot morphologies of interference field and the nonlinear error of interference fringe phase are measured. Results show that the waist radius of exposure spot is about 0.9 mm, and the nonlinear error peak-valley value of interference fringe phase is 21.8 nm.

The multiwavelength mode-locked fiber laser with a micro-fiber loop is proposed. The fiber laser is composed of two parts, the 8-shaped laser cavity and the micro-fiber loop. The mode-locked mechanism is based on the equivalent saturable absorption effect of nonlinear amplifying loop mirror. The micro-fiber loop fabricated through twisting the taped fiber is incorporated on the side of the unidirectional laser cavity, which results in a phase difference when the light with different wavelengths pass through the micro-fiber loop. Thus, the multi-wavelength mode-locked can be realized. In the experiment, the dual-wavelength mode-locked pulses are obtained by increasing the pump power and adjusting the polarization controller. The multi wavelength mode-locked fiber laser with all-fiber configuration has potential applications in optical sensing, optical measurement, microwave photonics, optical signal processing, terahertz generation and wavelength division multiplexing optical transmission system.

Supercontinuum laser is a new direction after the emergence of super-fast laser source and also a concentrated expression of multiple nonlinear optical effects. It can be used in the fields of spectral detection, microscopic measurement, chemical sensing and so on. The supercontinuum output of both ends of the fiber is obtained by using the tunable femtosecond laser at different wavelengths output to pump the sapphire fiber. Based on the characteristics of the continuous spectrum, the supercontinuum laser system is set up taking the ensemble of an optical fiber front end and semiconductor saturable absorber mirror (SESAM) reflector as the strong resonant cavity. The center wavelength of the final output is 640 nm with the full width at half maximum more than 250 nm. The results show that the SESAM cavity can weaken noise and output consistent wide-spectrum laser.

Excimer pumped sodium laser has the potential to realize the sodium beacon light source. During the operation of the laser, excimer is utilized to pump sodium atom from ground state to excited state, so it is necessary to experimentally study the fluorescence lifetime of excited sodium atom produced from dissociation of excimer pairs. In this work, sodium-ethane excimer pairs are excited by blue satellite pumping light with different wavelengths, and the fluorescence lifetimes of sodium D1 and D2 lines are measured at different operation temperatures. The experiment results demonstrate that the fluorescence lifetimes of 32P3/2 and 32P1/2 states are obviously longer than their natural lifetimes, the longer the excitation wavelength, the more obvious the extended fluorescence lifetime. Radiation trapping effect is considered as another factor that leads to the fluorescence lifetime lengthening. On the other hand, as the single photon energy decreasing, the probability of excimer pairs excited to A2Π3/2 state increases, and the excited sodium atom can be produced during a longer period, and this may also lead to the fluorescence lifetime lengthening. For sodium-ethane excimer pairs, the amplification characteristic of sodium D2 line amplified spontaneous emission signal is better than that of sodium D1 line. The better amplification characteristic and longer fluorescence lifetime make sodium D2 line laser easier to achieve.

Based on master-oscillator power amplifier structure, an laser output with high pulse energy and high beam quality is achieved using a specific orientation Nd∶YAG laser amplifier. The laser amplifier includes three parts, a seed laser source, a pre-amplifier stage and a main-amplifier stage. In the main-amplifier stage, a laser diode side-pump Nd∶YAG rod amplifiers is used for the amplification of the seed laser. In order to obtain a high beam quality output, the thermal depolarization losses for different cut Nd∶YAG rods are simulated. According to the simulation results, the ［100］-cut Nd∶YAG rods are chosen as the active materials in the main-amplifier stage. Under the condition of repetition frequency of 200 Hz, pulse width of 25 ns, pulse energy of 40 μJ and a near diffraction limit seed laser injected, an output of 425 mJ pulse energy is gained with a beam quality factor of 1.37, and the output power stability of 0.81%.

An all-normal dispersion tunable mode-locked fiber laser with a nonlinear amplifying loop mirror is experimentally investigated. The laser employs an all-polarization-maintaining figure-8 cavity consisted of main loop and nonlinear amplifying loop mirror. At 1030 nm, the stable mode-locked laser is initiated by adjusting two loops′ pump power, which delivers pulse width of 17.61 ps, repetition frequency of 4.133 MHz, and average power of 2.151 mW. A tunable filter is employed in the cavity to select the laser wavelength as well as force the laser operating in all-normal dispersion dissipative regime. The wavelength tuning range is 1015-1080 nm while the pulse duration ranges from 7.86 ps to 17.80 ps.

The locations and peak intensities of hot images are compared under high flux density when the damage point is located on the front surface and rear surface of upstream medium respectively. The phenomenon of alternate arrangement of hot images and variation rule of peak intensities with damage point size are discussed. For the fact that the damage point in upstream optical components is the major factor to induce hot images in subsequent optical path, the hot images prejudging technique is proposed, and the analysis object of which is diffraction rings image introduced by damage point propagation for a certain distance. This technique extracts the feature information of diffraction ring images by using gradient direction matching method with high signal-to-noise ratio and then calculates the diffraction distance and the size of damage point inversely. The diffraction images of single equivalent damage point produced by liquid crystal spatial light modulator is used to demonstrate the effectiveness of the proposed method. The capability of suppressing noise interference and its spatial resolution are analyzed by using the diffraction ring images caused by the actual damage point on the optical components, when multi-damage points are inversed by the proposed method.

The third-harmonic laser parameters of a laser driver similar to U.S. National Ignition Facility (NIF) in a high laser-flux state, such as space, time and energy, are measured by using the third-harmonic precision diagnostic system of Shenguang II (SGII) upgraded facility. The phase-type periodic structure introduced in the machining process of the quartz components of the terminal optical system is confirmed by improving the near-field resolution. The far-field focusing ability and the near-field transmission modulation characteristics of the terminal optical system in a high laser-flux state are studied. The results show that the phase-type periodic structure is an important reason which can result in an enhancement of third-harmonic near-field modulation.

We study the laser performance of c-cut Nd∶Lu0.99La0.01VO4 crystal end-pumped by optical fiber coupled semiconductor laser. Based on the spectral characteristics of the 4F3/2→4F11/2 energy level transition and the threshold conditions of four-level laser system, the experimental conditions to generate single- and dual-wavelength laser at 1068 nm and 1085 nm are calculated theoretically. The output characteristics of the single-wavelength laser at 1068 nm and 1085 nm generated in free running of this crystal are studied experimentally, and an Fabry-Perot etalon with sub-terahertz free spectral range is used to adjust the gain competition of two laser oscillating wavelengths at 1068 nm and 1085 nm. The stabilized and balanced output of multi-watt continuous dual-wavelength emission with a frequency offset of 4.4 THz is realized.

The stimulated Brillouin scattering (SBS) effect is an important factor affecting the power boost of single frequency narrow line width fiber laser amplifiers. Utilizing white noise as the radio frequency signal source, an all fiber laser system with three stage master oscillator power amplifier is designed and built by phase modulation technique. The relationship between the spectral widths of the signal light and the SBS thresholds of the fiber amplifier system is analyzed and studied. By changing the amplitudes of the white noise signal, the spectral widths of the signal can be accurately controlled, and the narrow line width quasi continuous laser output with a central wavelength of 1030.93 nm, a line width of 0.9 GHz and an average power of 90 W is obtained. The corresponding X direction and Y direction of the beam quality factors are 1.28 and 1.27, respectively. This research provides a reliable theoretical and experimental basis for the industrialization of high power single frequency narrow line width fiber lasers.

On the basis of three-dimensional finite-difference time-domain method, the mode and unidirectional-emission characteristics for a 5 μm-radius microcavity laser with radial waveguide are studied. Q factors and mode field patterns for high-Q transverse electric mode near the wavelength of 1550 nm are obtained. An AlGaInAs/InP circular microcavity laser with radius of 5 μm is fabricated by semiconductor planar processing technology, with a 1 μm wide output waveguide directly connected to the cavity. Continuous single mode lasing is achieved with a threshold current of 4 mA at the temperature of 298 K. The side mode suppression ratio of the laser is 33.4 dB when the injection current is 9 mA. On the basis of rate equation, the laser model intensity is fitted with the change of the injection current, and the spontaneous emission factor of the laser is about 5.5×10-3.

Multi-keV X-rays are used as backlighting sources of the radiography to diagnose plasmas in high energy density physics (HEDP) experiments. We study the characteristics of Ti-4.7 keV and Cl-2.7 keV X-rays driven by nanosecond laser at the SG-II laser facility. The results show that the X-rays from Cl plasma are primarily He-like and H-like line radiation, with 2.7 keV He-α line on the strongest line emission. In addition, the relative intensity of Cl X-rays is more than an order of magnitude compared to that of Ti X-rays under the current SG-II laser conditions. Therefore, the Cl X-rays can be used as the backlighting diagnosis.

The effects of three heat treatment methods which include annealing, solution hardening of two-phase regions, and solution and aging treatment on the microstructure and mechanical properties of TC4 titanium alloy formed by selective laser melting (SLM) are investigated. The results show that the fine acicular martensite is formed in the TC4 titanium alloy formed by SLM and there is nearly no β phase, which makes the TC4 titanium alloy have high strength and poor plasticity. After the 840 ℃/2 h/air-cooling (AC) annealing, the microstructure of TC4 titanium alloy is consisted of (α+β) phases, which makes TC4 titanium alloys have better strength and plasticity. After the 940 ℃/1 h/water-quenching (WQ) solution hardening, the staggered basket-weave (α+β) microstructure is obtained in TC4 titanium alloys, the strength decreases significantly and the plasticity increases because of the increase of β phase content and grain size. After 940 ℃/1 h/WQ+540 ℃/4 h/AC solution and aging heat treatment, the (α+β) phases are formed and uniformly dispersed, and the α phase coarsens, which result in the decrease of strength and the slight increase of plasticity. After heat treatment, the residual stress and the tendency of the strain cracking of TC4 titanium alloy decrease. The better strength/plasticity matching of TC4 titanium alloy formed by SLM can be obtained by the annealing heat treatment of 840 ℃/2 h/AC.

The propagation of femtosecond laser pulse in the air containing a small amount of oxygen molecule in excited state is investigated by numerically solving the propagation equation, and the numerical results in both normal and low atmospheric pressures are compared. The numerical simulation results show that when the air contains excited molecules, it will affect the propagation process of the laser pulse. The bigger the proportion of the excited molecules is, the greater the influence of it on the time and spatial distribution of the laser intensity will be.

A magnetic field is introduced into the laser welding process, and the butt welding experiment of DC51D+AZ galvanized steels and 6061 aluminum alloys and the tensile experiment of welding samples are conducted. The influences of the alternating magnetic field on weld formation, porosity defects, fracture morphologies, intermetallic compounds, and mechanical properties of Fe/Al welding joints are investigated. The results show that the tensile strength of welding joints is improved after the introduction of the magnetic field. The magnetic stirring can improve the welding morphology, reduce the number of pores in welding joints, refine the acicular FeAl3 phase, and inhibit the growth of brittle Fe/Al compounds, which thus improves the mechanical properties of welding joints.

With the method of mask projection and direct-writing etching on the front surface of silica glass by a 248 nm nanosecond excimer laser, the influence laws of laser pulse energy density, repetition frequency, scanning times on micro-groove cracks are studied, and the mechanisms of laser etching and cracking of silica glass are analyzed. The results show that the mechanism of silica glass etched by a 248 nm nanosecond pulse excimer laser is the joint effects of photoionization and thermal ablation. The laser energy density threshold range for the crack-free etching of JGS1 silica glass is 16-30 J·cm-2 and the etching rate can be up to 500 nm per pulse. With the increase of laser repetition frequency and scanning times, the micro-grooves are easily cracked because of the heat accumulation and plasma micro-explosion shocking. Based on the optimized laser processing parameters, when the width of micro-grooves is less than 100 μm, the processing of crack-free linear-type (the depth is less than or equal to 50 μm) and circular-arc-type (the depth is less than or equal to 28.5 μm) micro-grooves can be achieved.

Arc-shaped flanged beam structural parts are formed by the laser cladding technology with an inside-laser powder feeding head. The collapse of ends in thin-wall structural parts is avoided with the method of laser energy loading. Due to the feature that tracks with different layer heights can be cladded by using laser beams at different defocus positions, the unequal-height fan-shaped parts can be formed with the variable-attitude radial-scanning method and the curved arc-shaped parts can be formed with the variable-attitude circular-scanning method. The maximum relative dimensional error of the formed parts is -5.9%, the hardness is stable at about 690 HV, and the microstructure is dense and uniform without holes and cracks.

The luminescence property parameters of the Yb3+-doped bismuthate glass are investigated, and the energy transfer from those defect quenching centers such as Yb2+ and Bi3+ to Yb3+ is also discussed. Based on the optimized matrix composition and without the sharp decline of the fluorescence lifetime, the near-infrared emission cross-section of Yb3+ in glass is obviously increased, the absorption cross-section is reduced, and the capability of laser gain and the saturation pump intensity are both enhanced. By the efficient dehydroxyl process, the luminescence quenching effect of Yb3+ in the bismuthate glass may not be stronger than that in the phosphate glass. However, there exist probably some defect quenching centers such as Bi3+ and Yb2+ with unstable valence states in the bismuthate glass.

Based on the film design theory, we design anti-reflective coating for short and medium infrared based on chalcogenide glass. Based on calculation and analysis of material thermal stress, a mixed material M-11 is developed as the connecting layer, the parameters of the deposition process are optimized. and the coating structure is corrected based on its mechanical properties. We solve the problem of stripping of chalcogenide glass. The results of spectral tests show that the transmittance in the bands of 1.4-2.5 μm and 3.5-4.5 μm are 95.8% and 96.7%, respectively, which satisfies the requirement of infrared imaging system.

Diffracted wavefront quality is one of the important performance indexes of gratings. If there is Abbe error in the grating ruling engine, it will directly affect the positioning accuracy of grooves, thus affecting wavefront quality of gratings. The physical models of the Abbe error and the quality of the grating diffraction wave are established, to analyze the influence of the error on the wavefront quality. Aiming at the Abbe error, a kind of measurement optical path is designed based on dual-frequency laser interferometry, and the influence of Abbe error on diffracted wavefront of the grating is measured and simulated. Furthermore, the error control method based on double-layer grating table structure is proposed. Before and after revising Abbe error, the ruling experiments for two echelle gratings with the size of 80 mm×100 mm and groove density of 79 groove/mm are carried out. The results show that the diffracted wavefront error of the gratings in -36 blaze order is reduced from 0.529λ to 0.159λ (λ=632.8 nm) by the measurement and correction of the Abbe error, which effectively reduces the influence of Abbe error on the quality of grating′s diffracted wavefront.

Diode-pumped all-solid-state mode-locked Yb lasers can generate femtosecond lasers with high average power and narrow pulse width in 1 μm region. The lasers have important applications in such fields as ultrafast nonlinear frequency conversion, femtosecond optical frequency comb, and ultrafast spectroscopy. Using passive mode-locking and Kerr-lens mode-locking technologies, the femtosecond laser operation is realized in a series of novel Yb-doped laser mediums. In this paper, the progress of diode-pumped all-solid-state mode-locked femtosecond Yb lasers is reviewed. The technical approaches and development prospects of power scaling and pulse shortening are proposed as well.

To achieve the detection targets of the helium (He) lidar system and to measure the density of He atoms of the atmosphere at altitude of 200-1000 km, the parameters and performance of the He-density detection lidar system are designed, which mainly includes laser emitting part, optical receiving part, data acquisition and control part. According to the parameters of the He lidar, the relationship between the expected number of photons received and the distance under the conditions of different metastable He ［He(23S)］ densities, integration time and range bin is compared, in which it is found that the density of metastable He(23S) has the greatest influence on the signal intensity. The resonance fluorescence signals by Rayleigh scattering signals is calibrated at a common lower altitude to obtain a relative number density curve and signal-to-noise ratio (SNR) curve. The simulation results show that in the height range of 250~530 km, the relative error is less than 2% and SNR is more than 40 when the integration time is 30 min, the range bin is 50 km, and the density of He(23S) reaches the minimum. These results prove that the designed parameters of the system meet the detection requirement of He atom density in upper atmosphere and have certain reference value for the system implementation in the future.

The harmonic measurement error mechanism and performance improvement method of the direct-current fiber-optic current transformer (DC FOCT) are investigated. The mathematical models in the discrete domain of the closed-loop signal-detecting system and the moving average output filter are established. The simulation analysis is carried out on the frequency response characteristic of the transformer. The study results show that the forward gain of the closed-loop detection system and the order of the output filter are both crucial factors affecting the harmonic current measurement accuracy. The harmonic current measurement error can be effectively decreased by increasing the forward gain under the condition of the stabilization of the closed-loop system and simultaneously by reducing the order of the output filter. The test platform for the harmonic current measurement error of the DC FOCT is built. The experimental results show that, in the range of 50-1200 Hz, the measurement error of the model machine is less than 0.5% and the bandwidth is more than 10 kHz.

To effectively retrieve the geometric form factor of the ground-based lidar and to modify the echoed signal in transition region, a new geometric form factor retrieval method is proposed. The method takes advantage of the characteristic of space-borne lidar (Cloud Aerosol Lidar Infrared Pathfinder Satellite Observation, CALIPSO) that it can cover the detection transition area of the ground-based lidar. The geometric form factors in off-axial and coaxial modes are determined by the use of simultaneous lidar measurement data from the space-borne lidar and the ground-based lidar. The results are compared to the results of comprehensive Raman-Mie method and Su Jia′s method. In the transition region of the geometric form factor, the average relative errors of the aerosol backscatter coefficient can be improved by 25.4% and 10.4% compared to those of Su Jia′s method in off-axial and coaxial modes, respectively. This method overcomes the uncertainties caused by assumptive uniformity of the atmosphere in the horizontal measurement method of the elastic scattering lidar. It is more suitable for the widely-used elastic scattering lidar. The geometric form factor of the ground-based lidar can be routinely calibrated by use of the regular transit time of CALIPSO with stable features.