In order to reduce the carrier frequency error of the processed interferogram by using the Fourier transform method, and accurately recover the laser phase to be measured, we propose a phase retrieval method based on the propagation property of Gaussian beam. On the cross section of the Gaussian beam along its direction of propagation, the phase of the beam is a symmetrical convex or concave surface. The curvature of the convex or concave surface is related to the propagation distance. According to this property, the size of the carrier frequency is calculated and the phase to be measured is finally restored. In theory, the size of the carrier frequency can be calculated accurately, and the phase to be measured can be restored with high precision. Both numerical simulation and experimental results show that the proposed method can accurately recover the phase to be measured.

In the study of narrow linewidth laser light echol detection under strong background, we utilize spectral filtering method to filter out background light and improve the signal-to-noise ratio. For the grating filter system, the transmission of signal light through the atmospheric channel will cause the wavefront phase distortion, and this will have a certain effect on the filtering performance of the system, so it is necessary to study it further. Aiming at the application of grating spectral filtering in the laser atmospheric transmission detection direction, based on the laser atmospheric transmission theory and the grating diffraction principle, we establish the simulation model of the spectral intensity distribution of the grating when the incident light field is atmospheric disturbance light field. The influences of atmospheric coherent length and system structural parameters on system performance are analyzed. The system of the grating spectral filtering technology and the atmospheric applicable conditions are given. When the atmospheric coherent length r0 is greater than 0.05 m, sub-nanometer level spectral filter linewidth (full width at half maximum is 0.3 nm) is obtained, and the transmission of the effective spectrum exceeds 0.90. The results are verified by a large number of simulation experiments.

For the spatial periodic modulation that affects the output performance of high power laser systems, a novel method of compensating and controlling the spatial periodic modulation based on phase carrier is proposed and analyzed. First, the theoretical analysis shows that this method is able to control the spatial frequency of the spatial periodic modulation. The intensity of the spatial frequency is modulated by changing the magnitude of the phase carrier, and for the amplitude-type spatial periodic modulation, the period of the phase carrier can change the position of the maximum intensity of the spatial frequency. Then, the experiment on the effect of phase carrier on the amplitude-type spatial periodic modulation is carried out. The feasibility of the method is verified by experimental results and numerical simulations. The output near-field beam and the corresponding one-dimensional average power spectral density curve before and after the phase carrier modulation are compared. It is found that the peak value of the spatial frequency drops by an order of magnitude and decreases to near the background value after phase carrier modulation in the experiment. This method provides a new way to compensate and control the sensitive spatial periodic modulation in high power laser systems.

The steady-state temperature distribution of high-power semiconductor lasers is simulated, the thermal lens focal length and the variation of the slow axis divergence angle are calculated with the temperature distribution under different thermal power conditions. Results show that, under the same conditions the thermal power and the thermal lens focal length are approximately inversely proportional, and the slow axis divergence angle is approximately linear with thermal power. When the thermal power reaches 10 W, the thermal lens focal length is 568 μm, and the slow axis divergence angle increases about 10°. The slow axis divergence angle of the laser under different working current conditions is measured and the results show that the simulated values are consistent with the experimental values.

Electrical characteristics of biological tissues are significant for early diagnosis of tumor tissues. Through detecting the Lorentz force effect of the samples, magneto-acousto-electrical tomography is confirmed to have ability to implement early diagnosis of tumor tissues with recognition of changes in electrical conductivity of organisms. In all previous work on magneto-acousto-electrical tomography, incident ultrasonic pulses are generated from conventional piezoelectric transducers. To avoid the electromagnetic interference to the ultrasonic excitation system, the piezoelectric transducer is required to be placed far away from the detected sample. However, the long distance of ultrasonic propagation between the ultrasonic transducer and the sample limits further clinical research. Firstly, laser-induced ultrasound transducers based on photoacoustic effect are proposed. The optic ultrasonic transducers are polymer-nanomaterial composites formed by carbon black and polydimethylsiloxane, which are promising to generate high-frequency and high-intensity ultrasonic signals through decreasing the thickness of composite films. The acoustic fields generated by optimized laser-induced ultrasound transducers are then characterized, and laser-induced ultrasound transducers are applied in the magneto-acousto-electrical tomography experiment. The results indicate that the output pressure and bandwidth of the ultrasonic signals generated by the laser-induced ultrasound transducers are similar to or better than those generated by the piezoelectric transducers. -6 dB frequency bandwidth and acoustic intensity of the laser-induced ultrasound transducers are measured to be about 7.5 MHz and 2.5 MPa, respectively. Due to the absence of electronics and metal in the laser-induced ultrasound transducers, acoustic sources generated by the laser-induced ultrasound transducers are compatible with magneto-acousto-electrical tomography and insensitive to electromagnetic interference.

In optical free space coherent communication fine tracking system, the advantage of using fiber nutation or fast steering mirror nutation to detect angle error is reducing losses and simplifying system and so on. However, they both need mechanically moving parts. This paper proposes detection method of the angle error of signal beam without mechanical nutation by acousto-optic deflector. Theoretical model of signal angle error detection is built and the possible error source is analyzed. Meanwhile, the verifying setup is built, and the precision is better than 1/10 angle divergence of signal, which can not affect the heterodyne detection.

The long distance transmission of underwater laser pulse is simulated based on Monte Carlo method. According to the underwater broadening of laser pulse and the variation of pulse energy, the system uses a solid-state laser with the wavelength of 532 nm and the single pulse energy of 1 mJ as the emission source, and uses a telescope with the aperture of 100 mm and the field angle of 15° as the receiver. Low-density parity check codes (LDPC) and pulse-position modulation (PPM) are accomplished based on a field-programmable gate array (FPGA). The received signal after photoelectric conversion and sampling is transmitted to the host computer for post-processing. Finally, a pool experiment is used to verify the system performance based on the developed experimental system. The theoretical and experimental results demonstrate that the designed system with LDPC and PPM can obtain 2.34 dB coding gain at the same bit error rate (BER) under the condition of Jerlov Ⅱ water quality. Experiment shows that the system can achieve reliable underwater communication with BER of 10-5 and distance of 130 m.

Aiming at the pulse position modulation (PPM) system of asynchronous sampling at sampling frequency of 1 slot, we propose a clock synchronization technique based on guard time. One or more guard time are inserted into each PPM signal in the transmitter. Based on the fact that there are only background photons in these guard time, while other slots have the characteristics of both background photons and signal photons, we achieve clock synchronization. At the receiving end, the sampling data is counted periodically with the number of slots in PPM signal. Then, the coarse timing synchronization is carried out based on the statistical distribution characteristics of photon in guard time. Finally, the interpolation matching search method is used for the fine timing synchronization. The simulation results show that the proposed method can achieve efficient synchronization within the scope of large timing offset, and increasing the number of guard time or increasing the amount of statistics can achieve ideal system bit error performance.

The bismuth/erbium co-doped silica fiber (BEDF) is fabricated by combination of modified chemical vapor deposition (MCVD) technology with atomic layer deposition (ALD) doping technique. The melt stretching treatments are carried out, and its near-infrared luminescence characteristics are studied. The experimental results show that the transmission spectrum intensity of BEDF is decreased with the increase of the stretching length. At the same time, the luminescence intensities at 940 nm and 1100 nm ascribing to bismuth-related active centers (BACs), under the 980 nm pumping, are obviously increased with the increase of the stretching length, and when the stretching length is 1.5 cm, they are enhanced by 8.2 dB and 9.7 dB, respectively. After stretching treatments, the luminescence intensity enhancement of the 4.9 cm-long BEDF may result from the change of valence states of bismuth ions and the decrease of concentrations of BACs. These findings are of great significance for studying the near-infrared luminescent mechanism of bismuth related luminescent materials and improving the luminescent efficiency of luminescent centers.

In order to improve the transmission capacity of the radio over fiber (RoF) system, a bidirectional RoF transmission system is proposed based on the generation of frequency-quadrupled vector signal and wavelength reuse technique. For the downlink transmission, a stimulated Brillouin scattering-assisted narrow-band optical notch filter and a Sagnac loop are employed to generate a frequency-quadrupled vector signal directly in optical domain. At the base station, the unmodulated sideband of the downlink signal is filtered out by a polarizer and reused as the uplink optical carrier to achieve wavelength reuse. In the experiment, a quadrature phase shift keying (QPSK) signal centered at 24 GHz is generated by frequency beating. A 400 Mbit/s downlink QPSK signal at 8 GHz and a 400 Mbit/s baseband on-off keying (OOK) signal as uplink are used to evaluate the system performance over a 6.15 km fiber link. The feasibility of the proposed system is confirmed by the experimental result.

The slow light technology of high-bit rate modulation signals has potential applications in the fields of optical communications of the future and optical signal processing. A key technique of high-bit rate modulated sinusoidal signal and return to zero pseudo-random bit sequences (RZ-PRBS) pulse signal dynamic adjustable delay is achieved via the structure of semiconductor optical amplifiers (SOA) cascaded band-pass filter based on light filtering. For the high-bit rate sinusoidal signal, when the 5 GHz signal propagates through the cascaded system, the fundamental harmonic fractional delay of 40% and -10% can be achieved by altering the SOA injection current, respectively. For a RZ-PRBS optical sequence, 44.6 ps (96.3 ps) advance (delay) can be achieved by tuning the injection current at the wavelength of 1549.735 nm (1550.525 nm). Experimental data shows that the proposed optical filter structure can realize the adjustable delay of high-bit rate modulation signal by changing the injection current of SOA. In the case of precisely controlling the SOA injection current, the optical filter structure can be used for signal synchronization and bit-by-bit signal processing in a communication system.

A kind of vertical-cavity surface-emitter laser (VCSEL) side-pumped all solid-state laser is studied. A compact and stable Nd∶YAG solid-state laser is reported. The laser is side-pumped by VCSEL arrays, and the VCSEL arrays are collimated by microlens array. A cylindrical lens is used to reshape the pump beam into a linear beam to achieve high power density. Besides, the Cr4+∶YAG crystal is used as saturable absorber to be the passive Q-switch. The laser output with 40 Hz repetition frequency, 4 ns pulse width and single pulse energy of 2.1 mJ is obtained. The experimental results show that the laser can achieve stable laser output in a large temperature range. The laser has a compact structure and high resistance to detuning and vibration. It can be used as a light source for future space laser detection and other special environments.

The investigation on the interaction between femtosecond laser filaments in air and negative corona discharge in the needle-plane electrode is reported. The spatial distribution of electric field of the interaction is theoretically simulated and the phenomena of laser guided negative corona is observed experimentally during the interaction process. The setup is established to understand this process. Both the simulation and experiment results show that the electric field distributions with the strength higher than the threshold for avalanche ionization do exist during the interaction process. As a consequence negative corona is guided at the end of laser filament. The negative corona area can be altered through the control of filament length, which provides a new method to optically guide negative corona.

The research on medium-infrared thulium-doped fiber lasers at 2 μm wavelength is widely used in the field of laser medical, eye-safe radar, non-metal material processing, and electro-optical countermeasure system, it has an irreplaceable role compared with other wavelength fiber lasers. An all-fiber wavelength-tunable passively mode-locked thulium-doped fiber laser is reported. This laser realizes picosecond pulses and tunable wavelength by using a semiconductor saturable absorber mirror and a high-birefringence fiber optical loop mirror. This high-birefringence fiber optical loop mirror consists of a 2×2 coupler with output ports spliced to a high-birefringence fiber. The tunable picosecond pulse laser output is obtained by changing the temperature of the high-birefringence fiber in a fiber optical loop mirror. The center wavelength tunable range is from 1952 to 1967 nm, the tuning width is 15 nm, the repetition rate is 29 MHz, and the shortest pulse width is 6 ps.

784.9 nm and 808 nm laser diode (LD) pump Tm/Ho bonded laser is studied at room temperature. The gain medium is a Tm/Ho∶YAG bonded crystal formed by diffusion-bonding of Tm∶YAG and Ho∶YAG crystals. The Ho laser properties pumped by the two LDs are compared, including output power, beam quality, and wavelength. At low pump absorption power, the efficiency of laser pumped by 808 nm LD is slightly lower than that of the 784.9 nm LD, which verifies the wide applicability of the new laser realization mechanism based on Tm/Ho bonded gain medium in pump wavelength selection. Using 784.9 nm LD, the maximum output power of 1.89 W is obtained at room temperature, with an optical conversion efficiency of 26.4% and a slope efficiency of 40.78%. Using 808 nm LD, the maximum output power of 1.74 W is obtained at room temperature with an optical conversion efficiency and a slope efficiency of 24.4% and 40.31%, respectively. Under the two pump conditions, the laser wavelength corresponding to the maximum output power is near 2122 nm.

The femtosecond laser dual-mode two-photon polymerization fabrication method based on a spatial light modulator (SLM) is proposed. The fabrication modes of focus control scanning and patterned exposure are realized by the load of the corresponding holograms on the SLM. These two fabrication modes not only ensure the fabrication quality, but also increase the fabrication efficiency of two-photon polymerization. By these two different modes, the Rio Olympic emblem and patterns with different shapes are fabricated, respectively. The feasibilities of these two fabrication methods in the micro-nano fabrication field are verified.

A tunable femtosecond optical parametric oscillator is designed and built, and the signal light stability with different cavity lengths is studied. The output stability is improved by the method of power and wavelength locking respectively, and the cavity length is controlled by the proportional-integral control system. The effects of the two methods on improving the signal optical output power and spectral stability are compared. The output wavelength of the oscillator can be tuned from 1317 nm to 1610 nm. The standard deviation of signal output power and wavelength is promoted to 0.16% and 0.35% by using the power stabilization method over a period of 15 min, and to 0.25% and 0.03% by using the wavelength stabilization method over the same period of time. It proves that both the power stabilization method and the wavelength stabilization method are sufficient for output stability in optical parametric oscillator. The requirement of power stability and wavelength stability for the output signal of femtosecond optical parametric oscillator varies from different applications, this work compares and studies the locking effects of two locking methods, and provides experimental basis and reference for future research.

Spectral beam combining of a broad area diode laser is a promising technique for high power direct diode laser applications. Grating external cavity spectral beam combination is based on wavelength selection characteristics of the grating and external cavity diode laser technology to achieve the locking of the single emitter spectrum and the combination of all the sub-beam combining elements into one output. The beam quality of the output is equivalent to that of a single beam combining element, and the brightness and power are greatly improved. An experimental study on the coupler free grating external cavity spectral beam combining of two mini-bar stacks was presented. Spectral beam combination of 12 diode laser short array stripes was realized. The characteristics of spectrum, power, and beam quality of the output beam were analyzed. At the pump current of 70 A, the continuous output power of 578 W, spectral bandwidth of 10.26 nm, and electro-optical conversion efficiency of 46.5% were achieved.

Optical power of a 397.5 nm ultra-violet laser can be inhabited by the feedback loop based on acousto-optic frequency shifter. The laser power is stabilized through changing the radio frequency power of the frequency shifter by error signal obtained by feedback, and controlling the laser power by the Bragg diffraction of the frequency shifter. The characteristics of the ultraviolet laser generated through frequency doubling is analyzed. Finally, in the time domain, the fluctuation of ultra-violet laser is remarkably decreased from ±11.739% to ±0.053% by the feedback (220 times improvement). In the frequency domain of 1 Hz to 8000 Hz, the power spectra density of laser is dramatically reduced. Typically at 5 kHz, the power spectra density is improved from 9.6×10-5 dBV·Hz-1/2 to 1.9×10-6 dBV·Hz-1/2.

The new type of graphene like material, represented by molybdenum disulfide (MoS2), has many advantages of adjustable band gap, high modulation depth, and wide band saturable absorption. It is widely used in ultra-fast pulse laser. The MoS2 nanoscale solution is obtained by lithium-ion intercalation method. High quality MoS2 saturated absorber (SA) was prepared by ultrasonic, centrifugation, spin coating and drying. The MoS2 film is characterized by Raman spectroscopy and atomic force microscopy. The results showed that the film is a few-layer structure (2-3 layer) with good uniformity. The new MoS2 SA is placed in a W-type all solid state laser system, stable passive mode-locked operation at 1063.9 nm is achieved. When the pump power reached 6.86 W, the average output power of the mode-locked laser is 894 mW, the energy and peak power of monopulse are 10.28 nJ and 2.056 kW, respectively, and the pulse width is 5 ps.

The multi-physics simulation of laser melt injection process is conducted and the effects of electromagnetic compound field parameters on the distributions of the flow field, temperature field and particles within the molten pools are investigated, which is also verified by the experiment. The results indicate that, the addition of the electromagnetic compound field can suppress the fluid speed, but does not obviously influence the temperature field distribution. When the directional Lorentz force and the gravity force are in the same direction, the majority of reinforcement particles is trapped in the upper region of the laser melt injection layer, conversely, the majority is in the bottom region.

In order to reduce the reflectivity of polysilicon surface, a picosecond laser is adopted to fabricate array pores on the polysilicon surface. The action mechanism of each laser parameter on the texturing depth is analyzed and the optimal experimental parameters with laser power of 15 W, pulse frequency of 25 kHz, scanning speed of 0.9 m/s and scanning times of 2 are chosen. Based on these optimal parameters, the influence of textured pore pitch on the polysilicon surface reflectivity is verified, and the open-circuit voltage and the short-circuit current of different textured silicon wafers are simulated by the PC1D software. The results show that, there exist the most compact pores with the best morphology on the polysilicon surface when the pore pitch is 30 μm. The pore density is 1.17×105 counts·cm-2, the surface reflectivity is 6.95% and the photoelectric conversion efficiency of the polysilicon battery is increased to 18.45%.

Microstructures and room-temperature mechanical properties of GH4099 alloy fabricated by laser additive manufacturing after heat treatments are investigated. The results indicate that the microstructure of as-deposited sample is mainly composed of epitaxial growth columnar grains. After solution treatment at 1120 ℃, due to the occurrence of recrystallization, the columnar dendrites are replaced by fine equiaxed grains, and there are some twin boundaries in the grains. There is less difference in microstructures between the solution treated samples and the solution-aging treated samples, their microstructures are still composed of fine equiaxed grains, and the size of grains does not grow up. However, the γ′ phase precipitates in the γ matrix after the aging treatment. Compared with the tensile properties at room temperature of samples in three sates, it can be found that the solution samples have the lowest strength and highest plasticity, while the aging samples have the best performance with high strength and ductility at room temperature. The reason is that recrystallization fully takes place during the solution processing and the dislocation density is small, while the γ′ phase only precipitates after aging treatment, which can block dislocations movement.

In welding process, the flow characteristics of molten pool are closely related to the defects such as porosity, undercut and so on. It also has important influence on the crystallization process of molten pool and weld formation. The research objects of low-alloy high-strength steel are drilled holes and then filled with ZrO2 particles as tracer particles. And the position of keyhole, arc shape and flow characteristics of molten pool are recorded by high speed camera. The flow law of the molten pool surface during laser-GMAW hybrid welding is studied at different laser-arc distances. The results show that when the laser-arc distance is 1 mm, the keyhole is unstable and drift occurs. At the same time, the tracer particle flows to the rear along the central axis after circumventing the arc action zone. When the laser-arc distance is 3 mm, the position of the keyhole is relatively stable. However, the typical Karman vortex phenomenon appears during the flow of tracer particles. When the laser-arc distance is 5 mm, the keyhole position is stable, while the stagnation phenomenon of tracer particles appears as it flows through the middle region of laser keyhole and arc action zone. Under this condition, the moving distance of tracer particles is the largest. Comparing the cross-section morphology of the joints at three kinds of laser-arc distances, we can find that when the laser-arc distance is 1 mm, there are some pores at the bottom of the weld, which is caused by the unstable keyhole because of the small laser-arc distance. When the laser-arc distance is 5 mm, the distance between the two heat sources is too large, resulting in the increase of the coupling efficiency of the two heat sources, and significant decrease of the penetration depth. When the laser-arc distance is 3mm, the weld has no defect and the penetration depth is the largest.

In order to obtain the mechanism of laser ablation on the electrical properties of quartz fiber/epoxy wave-transmitting material under high density heat flux condition, we utilize continuous laser as heat loading source to carry out laser ablation, and test the dielectric constant of the material. The thermal damage evolution behaviors of quartz fiber/epoxy wave-transmitting material are obtained by the TG-DSC analysis of epoxy resin and quartz fiber. The infrared absorption spectrum and the crystalline material of ablation product on material after laser ablation are tested by transmission infrared spectroscopy and X ray diffraction, and the ablation morphology of the material is observed by scanning electron microscopy. The test results show that, after laser ablation at laser frequency of 7-17 GHz, the dielectric constant of the material dielectric constant is about 4.5, which is nearly 50% higher than before ablation. The laser irradiation makes the epoxy resin thermal decomposition and cracking, the graphite with conductive ability and chain state forms on material. At the same time, because of the rough and loose surface of the material, its reflection and scattering abilities on electromagnetic wave are enhanced, and the transmission capability is weakened.

The effect of laser wavelength on the droplet transition behaviors is studied in the laser-CMT hybrid welding process. The results show that, the droplet transfer process is influenced when the molten pool shape and wire-heating are changed by the laser, and the laser-CMT hybrid welding process is more stable than the CMT welding process. The CO2 laser has a relatively strong influence on the droplet volume. When the CO2 laser power is relatively low, the laser can promote the droplet transition. However, the laser prevents the droplet transition process when the laser power increases. The fiber laser has a less effect on the wire-heating, but can increase the transition frequency of droplets. The plasma temperatures from the CO2 laser and fiber laser increase with the increase of the laser power. The plasma by the CO2 laser presents a lump-like eruption but that by the fiber laser shows no eruption.

The 14 mm thick EH36 high strength steels are welded by the fiber-laser-MAG hybrid welding process. The effects of laser power, welding speed and welding current on the weld formation are investigated and the microstructures and perfomances of welded joint under the optimal process parameters are analyzed. The results show that the weld penetration increases and the weld width is basically unchanged with the increase of laser power. With the increase of welding speed, the weld width decreases and with the increase of welding current, the weld width is basically unchanged. Under the optimal welding process parameters, the weld formation is good and there are no welding defects. The microstructures of the heated affected zone and weld zone are mainly composed of lath martensite. The hardness of weld metal is greater than that of the base metal. The fracture position of the tensile specimen is within the base metal. There are no cracks on the tensile surface after the transverse bending test. The fracture morphology of weld impact specimen is quasi cleavage fracture.

Cobalt-based superalloy DZ40M sample is prepared by laser additive manufacturing method and its microstructure is studied. The microstructure and mechanical properties of the alloy under different heat treatments are compared. Results show that the dendrites size of DZ40M microstructure obtained by the laser additive manufacturing method is finer than the traditional directional solidification structure, and the tensile strength and plasticity are improved in different degrees. Solution treatment under 1280 ℃ can make the primary carbide achieve full solid solution and new eutectic structure appears. Then after 950 ℃ or 1020 ℃ aging treatment, the secondary carbides are obtained. The samples after aging treatment show better mechanical properties. Especially, 1280 ℃/4 h+1020 ℃/12 h heat treatment system can improve the tensile strength at room temperature and keep the maximum degree of ductility of the deposition state sample.

In order to reduce the production cost of copper alloy 3D printing, we use the Cu-10Sn alloy powder prepared by water atomization as raw material for laser selective melting (SLM) experiment, in order to obtain an almost completely dense Cu-10Sn alloy bulk sample by optimizing the SLM processing parameters. The relative density of the sample could be reached to 99.7%. The sample consists of two phases of intermetallic compound Cu41Sn11 and α-Cu solid solution. The grain morphology is mainly the columnar dendrite and interdendritic phases formed along the solidification direction, and high density dislocations are distributed within the crystals. Under the quasi-static tensile condition, the yield strength of the specimen is (392±6) MPa, the tensile strength is (749±5) MPa, and the plastic deformation is 29%±2.3%. The comprehensive mechanical properties are much higher than those of Cu-10Sn alloys prepared by casting methods.

Based on high-reflection layers and the Gires-Tournois (G-T) cavity, a low oscillation and high dispersion mirror pair is optimized and designed, whose central wavelength is 800 nm and which can provide a constant group delay dispersion of -200 fs2 over a bandwidth of 680-920 nm. The low oscillation and high dispersion mirror pair is prepared by using Nb2O5 and SiO2 based on the dual ion beam sputtering process, which is used in the 800 nm Ti∶sapphire laser system. The laser pulse can be compressed from 100.8 fs to 19 fs when the pulse travels through the high dispersion mirror pair for twice.

The ZnO nanowires are treated by the Ar+ plasma and the changes of luminescence properties before and after treatments are analyzed by the test of temperature-dependent spectra under different treatment time. The results show that the near band edge emission intensity at room temperature increases first and then decreases with the increase of treatment time. As for the treatment time of 90 s, the intensity is 2.45 times that of the as-grown sample and simultaneously the defect-related photo-luminescence in visible region is suppressed. The mechanism of plasma treatment is analyzed by the comparison among luminescence spectra at 10 K. When the treatment time is short, the impurities and defects on the ZnO nanowire surfaces can be effectively removed by the Ar+ plasma and thus ultraviolet luminescence intensity is enhanced. When the treatment time is relatively long, the crystal structure is broken due to the introduction of more deep donor-state defects and thus the luminescence property is reduced.

The silicate glass doped with CdTe quantum dots is prepared by the high temperature melt-quenching technique and the Raman, absorption and emission spectra are tested. The quantum size effect of quantum dot doped glass is verified. The up-conversion fluorescence of the CdTe quantum dot doped glass is excited by 800 nm and 960 nm femtosecond lasers, which is confirmed to be two-photon absorption induced luminescence and the two-photon fluorescence possesses a requirement for a certain range of wavelengths. The nonlinear absorption coefficient of the CdTe quantum dot doped glass is obtained up to 3.62×10-11 m·W-1.

The rapid transversal growth method based on continuous filtration is applied to effectively increase the Z-direction length of the potassium dihydrogen phosphate (KDP) crystal and improve the II-type plate yield of the unit crystal. Different doses of γ ray are used to irradiate on the II-type crystal. The optical performance and the laser induced damage threshold are tested. The research results show that different doses of γ ray irradiation do not change the lattice vibration modes within crystals, but can reduce the vibration intensity of the lattice at 912 cm-1. The defect types induced by the γ ray irradiation do not change, but the defect density increases with the increase of the irradiation dose. In addition, the laser induced damage threshold of crystal plates decreases with the increase of the irradiation dose.

Three-dimensional (3D) point cloud data are widely used in intelligent driving, remote sensing, and virtual reality. This study presents a 3D point cloud classification algorithm that classifies large outdoor scenes effectively and accurately. First, the algorithm eliminates outliers from the original point cloud. Then, based on the off-the-shelf ground-filtering algorithm, it leverages difference of norms to filter ground points. Then, it uses the density-based spatial clustering of applications with noise (DBSCAN) clustering algorithm to segment non-ground point cloud. The nearest fusion strategy is used to solve the oversegmentation problem of the point cloud. Then, the proposed algorithm extracts global features that represent different objects from the point cloud, including vertical slice sampling and centroid distance histograms, as well as histogram of oriented gradient (HOG) features representing a two-dimensional projected image of the point cloud. Finally, a support vector machine (SVM) classifier is used to obtain the accurate 3D point cloud classification results. The experimental results reveal that the proposed algorithm can classify complex large outdoor scenes into accurate single objects with high accuracy and high recall rate. The proposed algorithm is more efficient compared with other algorithms.

Aiming at the saturation drift error occurring in the identification method of the constant ratio timing which is commonly used in laser fuze, an identification method of the composite moment between the front edge discrimination and the constant ratio timing and its error compensation model are proposed. The drift error model for the identification of the constant ratio timing is established and the variation law of the saturation drift error with the theoretical peak voltage of echo signals is analyzed. The compensation method of drift errors based on the composite moment identification method is proposed, and a mathematical model for compensating drift errors in the identification of the composite moment is established. The modified pulsed laser ranging formula is obtained and the verification experiment of the measurement precision is carried out. The results show that, the system errors can be effectively reduced by the composite moment identification and the error compensation correction methods and the ranging precision can be controlled within ±0.3 m or less.

On the basis of the particle scattering imaging, the refractive index of the particle can be obtained by the distance between the zero-order and the first-order spectra on the focal plane. The influences of the received angle and the magnification deviation of the imaging system on the measurement accuracy of the particle refractive index are analyzed. And the ranges of the received scattering angles and the magnification are given. An experimental method based on linear fitting is proposed to accurately determine the scattering angle and the magnification. The refractive indices of standard polystyrene (PSL) particle with diameter of 45 μm and glass particle with diameter of 19.1 μm are measured with the proposed method, their relative measurement errors are -0.19% and 1.53%, respectively. The experimental results verify the effectiveness of the proposed method.

The three-dimensional reconstruction method based on digital speckle correlation technique is introduced in detail, including the basic principle of binocular stereo vision and the three-dimensional reconstruction process. The integer pixel search method and the subpixel interpolation algorithm based on Newton-Raphson iteration are emphatically analyzed, and the subpixel-level reconstruction is realized. According to the correlation model, the factors affecting the correlation coefficients are analyzed. Three-dimensional reconstructions by the binary and 8 grayscale speckles are discussed in terms of coefficient calculation and subpixel location precision. The ceramic plate and the ceramic standard ball are reconstructed by patterns with different speckle sizes and correlation region sizes in the experiments. Test results demonstrate that the reconstruction by the binary speckle has a better performance.

The effect of filtering on the suppression of time-delay signature in the output signal of the optical feedback chaotic semiconductor laser is studied experimentally. Under the condition of the chaotic signal 100 MHz and 500 MHz low pass filter, the peak values of the autocorrelation coefficient and the permutation entropy at the feedback round trip time are used to quantitative extract the time-delay signature. The time-delay signatures with various feedback strengths are measured at different bias currents. The results show that the filtering effect suppresses the time-delay signature of the chaotic signal effectively. Under the condition of 1.5Ith bias current and -7.5 dB feedback strength, the autocorrelation function near the external cavity delay decreases from 0.264 to 0.036, and the permutation entropy increases from 0.985 to 0.997. Meanwhile, the peak value of the autocorrelation coefficient at the feedback round trip time is inversely proportional to the permutation entropy with the feedback strength increasing. The results also show that the complexity and strength of chaotic laser first rise, and then fall with the increase of feedback strength. The filtering effect induces the complexity of chaos to approach the maximum under lower feedback strength, and the complexity remains unchanged with the feedback strength increasing. Moreover, the filtering can also improve the intensity distribution and enhance the symmetry of probability-density function, which leads to substantial increase in the rate of random number generators.

The laser pulse emitting from the ocean lidar would be stretched while it travels through the deep sea water, and the waveform received by the ocean lidar is quite different from the emitting signal. Therefore, the normal matched filtering algorithm using emitting signal as the matched filtering has a bad performance in processing ocean Lidar data. To improve the performance of matched filtering algorithm, Mento Carlo method is used to simulate the signal waveforms at different depths. The simulation waveforms are used as the matched filtering at the corresponding depth. The adaptive depth extraction algorithm is tested on the data set which is measured in the South China Sea. The test shows that the adaptive depth extraction algorithm is more accurate and robust on ocean lidar data set. A set of single beam sonar data is used to evaluate the accuracy of depth using the adaptive depth extraction algorithm.

This study simulates the surface-tip-enhanced Raman scattering (SERS-TERS) model of a stepped tip with a silver film and a silver-nanoparticle-active substrate. The simulation is established by the finite-difference time-domain method. The near-field electric field distributions of different types of needle tips and substrates are numerically calculated under the same conditions, verifying the effectiveness of the designed method in the Raman scattering enhancement. Next, the electric field intensity of the model is systematically analyzed under different influencing factors: the curvature radius of the tip, the thickness and height of the silver film on the tip, the diameter of the silver nanoparticles, the gap between the tip and the silver nanoparticles, and the incident angle. The field enhancement factor is maximized at a tip-curvature radius of 5 nm, a silver-film thickness of 25 nm, a silver-film height of 300 nm, a silver-nanoparticle diameter of 55 nm, a 1 nm gap between the tip and silver nanoparticles, and an incident angle of 45°. The largest enhancement factor is of the order of magnitude of 107. The simulation results provide an important theoretical basis and experimental guidance for preparing high-efficiency tip and TERS active substrate structures.

Terahertz three-dimensional (3D) imaging is an important research direction for terahertz (THz) imaging technology, because 3D images of a sample can provide richer distribution information than 2D images. The main algorithm-control parameters that affect the accuracy of compressed 3D reconstructions are the number of iteration and the sparse restriction parameter. In this paper, we use subjective and objective evaluations to analyze the influences of these parameters on the reconstruction results for an ideal situation. Considering that noise is generated because the actual target plate is inhomogeneous, we mainly study the influences of the control parameters in reconstruction algorithms containing different levels of Gaussian noise on reconstructed results. The results show that when the number of iteration is 200, sparse restriction parameter is 0.02, 0.1 and 0.1 for the ideal case and Gaussian noise variance of 0.0005 and 0.001, respectively.