Starting from the nonlinear Schrodinger equation and by means of split-step Fourier numerical simulation,we study the propagation characteristics of Airy-Gaussian (AiG) beams in a photorefractive media. The results show that a specific set of parameters can result in soliton with periodic oscillation in the photorefractive media. The bigger the nonlinear factor is, the shorter the distance required to form soliton is, and the smaller the oscillation period of the soliton is. When the initial incident power of the Airy-Gaussian beam is within a certain range, the stable soliton can form. In the process of soliton formation, local energy competition leads to beam splitting. In addition, we also check the stability of the beam by perturbing the initial Airy-Gaussian beam.

This study presents the design of a metal-insulator-metal curved waveguide filter coupled with an embedded-silver-bar disk cavity, which is based on the transmission and coupling characteristics of surface plasmon polaritons. Herein, the spectral and filtering characteristics of the proposed structure are analyzed via the finite element method. The results indicate that the dual-mode resonance effect is achieved because the silver bars embedded into the disk cavity destroy the structural symmetry. In addition, the structure possesses the bilateral coupling effect, which makes the coupling efficiency higher than that for single-sided coupling. There exist two distinct forbidden bands in the transmission spectrum and the good dual-band narrowband filtering function is obtained. Furthermore, a quality factor higher than those of the previously reported filters is achieved. The wavelength of such a filter can be approximately linearly adjusted by varying the radius of disk cavity or the refractive index of the medium in the cavity.

In conventional photoacoustic (PA) imaging, the tissue absorption coefficient is usually considered to be a non-directional scalar constant, and its anisotropic optical absorption characteristics are ignored. Herein, we propose an anisotropic PA microscopy (A-PAM) technique that uses two linearly polarized light beams perpendicular to each other as the excitation source for PA imaging. Subsequently, we develop the A-PAM imaging system and verify the feasibility of the proposed method using phantoms that exhibit different forms of anisotropic optical absorption. Furthermore, we demonstrate the imaging ability of this method using biological samples that exhibit anisotropic absorption. Results show that the proposed method can be easily implanted into the conventional PAM imaging system, expanding the range of information extracted using conventional PA imaging.

Polarization-maintaining micro/nanofibers have various applications in fields including optical communication, sensors, nonlinear optics, and quantum optics. Temperature stability is a key factor in the numerous applications of such fibers. Herein, the temperature characteristics of birefringence of polarization-maintaining micro/nanofibers are studied through experiments and software analysis. By using the polarization interference method, a blue-shift interference spectrum can be obtained with the increase of the temperature. The relationship between temperature and birefringence is obtained. The experimental results show that the influence of temperature on polarization-maintaining micro/nanofibers is much less than that on ordinary polarization-maintaining fibers. The measured results are consistent with the theoretical results.

Visible light communication (VLC) is prone to overlap coverage of the adjacent VLC access points (APs), receiver occlusion, and light path interference. This study develops an AP selection algorithm for heterogeneous VLC/wireless fidelity (WiFi) networks. By considering the joint demands of transmitting and receiving, the algorithm employs a quality-of-service (QoS)-based decision-making to satisfy the differentiated resource demands of the receiving end and the transmitting equipment. First, it designs a QoS-oriented weighted information matrix for each receiver and guides the user to select the VLC AP with high received signal-to-interference-and-noise ratio, high received power, low traffic load, and low historical interruption probability. Guided by the same algorithm, the selected VLC AP preferentially serves users with strong anti-interference. Finally, to optimize the AP access, we improve the weights of the APs and users based on gravitation theory. In simulations on a uniform square layout and a mixed circular-square layout, the proposed algorithm delivers 77.3% and 11.4% more throughput respectively than the existing algorithms, and reduces the service fairness index by 53.1% and 41.1%, respectively.

This paper proposes an internally modulated chirped pulse based direct detection type phase sensitive time domain reflectometer (φ-OTDR) system with high signal-to-noise ratio (SNR). Based on theoretical analysis, we find that the stimulated Brillouin threshold increases with the increasing injection pulse energy, the high direct current component of the detection signal keeps the signal and noise separate, and the SNR can be enhanced. Then a statistical evaluation method is proposed to calculate the SNR of the sensing system. Meanwhile, an internally modulated direct detection type φ-OTDR system based on the distributed feedback laser is experimentally studied. The frequency chirp range introduced by internal modulation is controlled by the tunable filter. Compared with the traditional φ-OTDR system, the proposed system can obtain similar SNR and smaller distribution variance and realize higher measurement reliability. Additionally, The proposed system has the advantages of low cost and small volume, and the tunable filter can be replaced by fiber Bragg grating in practical application. It can improve the flexibility of application and provide a new idea for engineering.

Based on passively mode-locked Yb-doped fiber lasers, the effect of intracavity filtering bandwidth on the generation of bound-state solitons in normal dispersion regime is studied experimentally. A heavily Yb-doped fiber as gain medium and a semiconductor saturable absorber mirror as mode-locked element are used to obtain the 1064 nm all-fiber linear cavity mode-locked laser. Different picosecond mode-locked pulse states are observed when the bandwidths of 0.2, 1.0, 1.2, and 2.3 nm of intracavity bandpass filter are selected. When the filtering bandwidth is narrow (0.2 nm) or broad (2.3 nm), only stable dissipative solitons are obtained. In contrast, when the filtering bandwidth is moderate (1.0 nm or 1.2 nm), we respectively observe the typical π and -π/2 bound-state dissipative solitons both with the pulse width of 3 ps and pulse interval of 14 ps. Then the bound-state soliton laser is amplified to 1.4 W by the master oscillator power amplification technique and injected into a photonic crystal fiber, generating the supercontinuum spectrum with the spectral width of 10 dB in 750-1600 nm and the output power of 0.7 W, whose spectral flatness is better than that pumped by the traditional dissipative soliton.

Aiming at the problem of large number of pilots and low efficiency and accuracy in existing channel estimation algorithms of relay-and-forward indoor visible light communication systems, a channel estimation method based on tensor mode noise compensation is proposed. Firstly, a pilot structure which is suitable for noise compensation for the received data is designed by making the best of the characteristics of the transmission data structure in visible light communication. Then, according to the framework of PARATUCK2 tensor decomposition, a communication system with noise model of this pilot mode is constructed. Finally, combined with the tensor decomposition method, a method of estimating the real noise with noise compensation of pilot frequency is designed, and all channel parameters are estimated. The simulation results show that the estimation algorithm based on tensor mode noise compensation can be applied to the relay-and-forward indoor visible light communication system, accelerate the iteration speed, and improve the estimation accuracy, which fully verifies the effectiveness and feasibility of the algorithm.

To solve the mechanical damage caused by direct contact when the fiber optic tweezers captures particles, a single fiber long-distance capture method based on photothermal effect is proposed. Mesoscale silica spheres can be moved and trapped freely within 800 μm by utilizing a C-band fiber broadband amplified spontaneous emission source with a power of less than 20 mW. To find out the capture mechanism, COMSOL Multiphysics finite element analysis software is used to simulate the temperature field distribution, convective velocity field distribution, and particle motion trajectories when the fiber is at different heights in the silica suspension. It is shown that the drag force generated by the heat convection plays a crucial role in the process of the manipulation of microparticles, while the capture speed and capture distance can be changed by adjusting the fiber height. The optical fiber microfluidic device has the advantages of simple structure and flexible operation, and can realize large-scale capture of large particles by using low-power lasers.

We propose an unstable ring resonator to transform the nonconjugation correction of intra-cavity aberrations in the traditional standing-wave unstable resonator into conjugation compensation. A 100 W-order Nd∶YAG slab laser with the unstable ring resonator is constructed, with a 59-element adaptive optics system compensating the intra-cavity aberrations. A 980 nm reference beam and a Shack-Hartmann wave-front sensor are employed to measure the intra-cavity aberrations. Then the weighted least square method is applied to reconstruct the aberrations. The tip/tilt mirror and deformable mirror are used to correct the aberrations. With the aberrations compensated by an adaptive optics system, the output power increases from 105.8 W to 113.1 W and the beam quality factor improves from 6.98 to 2.33 under a relatively low pump power. The study provides a technical approach for high power solid-state unstable ring lasers to achieve high beam quality.

The working stability of an optically-addressed phase-only spatial light modulator is analyzed and optimized based on the equivalent circuit simulation of the optically-addressed spatial light modulator and an experiment to measure its stability. The results demonstrate that the voltage waveform on the liquid crystal layer of the light valve causes the phase fluctuation of the readout light modulated by the optically-addressed spatial light modulator and that the driving voltage frequency and write light intensity simultaneously affect the modulator's phase fluctuation amplitude and phase change capability. Based on the aforementioned analysis and by testing the phase change curves of the optically-addressed spatial light modulator, it is found that when the driving voltage period is 95% less than the response time, the phase fluctuation rate corresponding to the maximum phase change of the phase modulation curve is reduced to 0.35%; however, the phase modulation capability is only 0.8λ. By optimizing the driving condition parameters of the optically-addressed spatial light modulator, a phase modulation capability of 1λ is obtained, and the phase fluctuation rate corresponding to the maximum phase change of the phase modulation curve is 1%.

In this study, we describe a multi-wavelength laser at wavelengths of 634, 644, and 655 nm based on cascaded nonlinear frequency conversion. The cascaded frequency conversion process is jointly performed using the KTiOPO4 (KTP) and KTiOAsO4 (KTA) crystals. First, optical parametric oscillation is conducted in an x-cut KTP crystal to convert the 1064-nm laser into a 1572-nm laser. Sum frequency generation is subsequently achieved in a (θ=90° and φ=20.9°)-cut KTA crystal for the sum frequency mixing of 1064 and 1572 nm, generating a 634-nm laser output. Raman frequency conversion is further utilized in the x-cut KTP crystal to convert the 634-nm laser into first-order Raman radiation at 644 nm and second-order Raman radiation at 655 nm, simultaneously achieving multi-wavelength emissions at 634, 644, and 655 nm. The cascaded frequency multi-wavelength laser has a maximum average output power of 1.7 W, a pulse width of 19.3 ns, and a repetition rate of 6 kHz.

This study proposes a structural design for a breath soliton erbium (Er)-doped fiber laser under a relatively low (100 MHz) repetition rate to obtain a pulse output having narrow pulse width. An output pulse with a large breathing ratio can be ensured by shortening the lengths of the positive and negative dispersion fibers with a large dispersion coefficient in the cavity. And, a fiber with zero dispersion is introduced to reduce the repetition rate of the laser. The energy loss of the pulse in the cavity is reduced using a fiber optic mixer, which integrates the wavelength division multiplexer and the isolator with the forward pumping method. The distribution of the negative dispersion fiber in the cavity is optimized and designed to determine the output position of the laser. Based on this, a breath soliton Er-doped fiber laser having a repetition rate of 100 MHz is constructed; the laser's output spectrum and direct output pulse width are 112 nm and 68 fs, respectively. After dispersion compensation, the laser's output pulse width is 39 fs, and its average power of output pulse is 94.5 mW at a pump power of 900 mW.

To obtain a mid-infrared HF laser with high repetition rate and high power, a closed-circle pulse-periodical non-chain HF chemical laser with self-acting ultraviolet pre-ionization and a pair of symmetrical Chang electrodes is developed. The design and performance of the developed laser are described in detail. An experimental study on the laser output and repetition rate operation characteristics demonstrates the effect of repetition rate on pulse energy. The average power for a HF laser with a repetition rate of 150 Hz is approximately 200 W when the gas flow speed is 16 m/s in the gain region, working voltage is 25 kV, and the total mole fraction pressure of 92% SF6 and 8% C2H6 gas mixture is 8.5 kPa.

The key nodes of laser subsystems on the Shanghai Ultrafast Laser Facility are selected to measure the laser beam wavefronts, and then the origin, evolution, and causes of wavefront distortion are analyzed. Further, the effects of installation stress of optical devices and quality of Ti∶sapphire crystals on the wavefront are investigated. The results demonstrate that the laser wavefront distortion increases with the increasing number of large-aperture optical devices. Facet fabrication and installation and debugging errors of optical lenses are particularly important factors affecting wavefront distortion in a Ti∶sapphire laser amplifier. Such errors greatly affect the focusing ability of the laser. Measuring the wavefront of the laser system can help optimize and control the wavefront distortion of the entire system. In addition, such measurements can improve beam quality, focal spot properties, and focusing power density.

We explore the gamma radiation characteristics of double-layer targets driven by nanosecond/picosecond two-beam lasers based on the Shenguang II upgrade laser facility. A nanosecond laser is used to interact with a thin film target to generate a large-scale near-critical density plasma. Further, a picosecond laser interacts with the plasma to generate high-energy electrons. The high-energy electrons pass through a 2 mm thick Au target to generate gamma rays via bremsstrahlung. Subsequently, the experiments measure the gamma energy spectra in different directions and gamma doses outside the target chamber. It is found that the gamma radiation is concentrated in the picosecond laser propagating direction with a small divergence angle, and the high-energy parts of the gamma rays are enhanced in this direction as well. The design of the double-layer target can improve the energy coupling efficiency of the picosecond beam and plasma, increase the temperature and number of high-energy electrons, and facilitate the concentration of high-energy gamma radiation in the propagating direction of the picosecond laser beam. Furthermore, the single-shot maximum dose of gamma radiation, which has energy higher than 50 keV and is measured at 1.25 m from the target outside the target chamber, is 277 μGy. Results of the present study could be considered as references for the shielding and application of gamma radiation.

The requirements of precision guidance characteristics of a semi-active laser-guided weapon on the laser-coded pulse interval ΔTi were analyzed herein based on the pulse interval coding method. The generation principles of( the linear-feedback shift register) (LFSR) modulation code and the LFSR status code were studied and simulated. The guidance and anti-interference performances were studied based on the value range and generation method of the pulse interval ΔTi of two codes. This study reports that the LFSR modulation code is not conducive to accurate guidance and is susceptible to accurate frequency code interference with a minimum pulse interval ΔTmin. The LFSR status code overcomes the problem of poor precision guidance characteristics of the LFSR modulation code, and of being susceptible to accurate frequency code interference with the ΔTmin period; however, the problems that the required identification parameters are few and the anti-interference is not strong still remain. This study uses a matrix to complete the register state transition, instead of the LFSR and the function of the modulo-2 adder, based on finding the coding with a high guidance performance and a strong anti-interference performance. A pseudo-random code based on the matrix remainder is proposed and applied. The theoretical analysis shows that the anti-interference performance of the pseudo-random code is better than that of the LFSR status code.

Herein, to obtain an integrated structure of circular polarization and laser output, we design a compound structure composed of gain and loss microcavities, magnetic microcavity, and metal layers. We use a 4×4 transfer matrix to study the optical properties of the structure. Results show that the compound structure can result in an intense Faraday rotation effect and gain transmission mode, and form multiple laser outputs with elliptical or circular polarizations in a certain range of structural parameters. In addition, for some specific structural parameters and wavelengths, the structure can produce an ultra-intense laser with circular polarization.

A pump laser drive circuit with high precision and high stability is designed based on frequency compensation technique. The laser can be operated in two modes: automatic current control (ACC) and automatic power control (APC). The drive circuit considers the current adjustment of the deep negative feedback system as the inner loop and the optical power feedback adjustment as the outer loop. Simultaneously, by combining first-order artificial analysis and Tina SPICE simulation, the frequency compensation of the loop is performed to realize high stability control of the pump laser. The drive chip is controlled via analog proportion-integration-differentiation technology to regulate the current of a thermoelectric cooler. The designed drive circuit supplies continuously adjusted output current in ACC mode; it has the following functions: slow start, reverse current prevention, and over-current protection. In ACC mode, the long-term stability of the output current reaches 0.04%. In APC mode, the long-term stability of the laser output power is better than 0.3%, the control linearity reaches 0.9999,and the long-term stability of the temperature control is better than 0.0928%. The experimental results demonstrate that this driving system has high security, high stability, and is easy to use.

In order to reveal the generation mechanistic of laser-induced breakdown spectroscopy characteristic difference between liquid and solid matrices, spatial evolution characteristics of Cr-element emission spectra, electron temperature, and electron density of the plasma generated via the pulsed laser ablation of a CrCl3 aqueous solution using liquid jet sampling technology are investigated. Results show that the laser-induced plasma in the liquid matrix has distinctly different spatial evolution characteristics compared with that in the solid matrix. Along the direction of the laser beam, the plasma can expand up to 0.8 mm away from the jet surface and the plasma plume has a small linear diameter of approximate 3.2 mm. Further, the maximum intensities of ionic and atomic spectral lines appear 0.8 mm and 0.4 mm away from the jet surface, respectively. Simultaneously, the electron temperature and electron density of the plasma are small and slightly vary within 2939-3611 K and (0.0149-4.86)×1014 cm3, respectively, along the laser beam direction. Maximum values are observed at 0.8 mm away from the jet surface. Similar to the solid-matrix plasma, the spatial evolution characteristics of plasma emission spectra, electron temperature, and electron density of the liquid-matrix plasma have good spatial symmetry.

This study proposes laser-induced arc hybrid welding technology for 6061 aluminum (Al) alloy/DP980 high-strength steel lap jointing with a nickel (Ni) interlayer, which achieves a good connection between 6061 Al alloy and DP980 high-strength steel. The effect of Ni interlayer on the mechanical properties and microstructure of the lap joints and the effect of the Ni interlayer in the welding process are analyzed. An optical microscope, a scanning electron microscope, an electron probe, and an X-ray diffractometer are used to analyze the microstructure and elemental distributions of typical lap joints. Experimental results show that adding a Ni interlayer between Al alloy and high-strength steel can effectively prevent the diffusion of Fe element into aluminum alloy matrix and change the types and distributions of intermetallic compounds (IMCs) at the 6061/DP980 interface. With the Ni interlayer, the IMC-layer thickness reduces obviously, and the IMC layer primarily contains FeAl3 and Fe2Al5. Simultaneously, the Ni element is mainly diffused in the form of an Al-Ni compound and an Fe (Ni) solid solution in the weld. The shear tensile load of the joint with the Ni interlayer can reach a maximum of 173 N/mm, indicating an increase of ~35% compared to that of the joint without the Ni interlayer.

To investigate the anisotropy of the tensile strength caused by laser cladding deposition, the influence of the scanning direction (from high to low and from low to high) on the microstructure and mechanical properties of the ramp's thin-walled part is explored based on the variable thickness cladding layer deposition. Tensile strength and hardness at different positions on the ramp's thin-walled part are tested, and its microstructure is analyzed by comparing it with that formed via uniform thickness cladding layer deposition. Results show that the grain growth direction in the longitudinal section is affected by the scanning direction when variable thickness cladding layer deposition is used. Furthermore, the grain growth direction and scanning track influence the tensile strength at different positions of the thin-walled part. Tensile strength anisotropy can be obviously reduced by depositing the variable thickness cladding layer in the scanning direction from low to high. In the horizontal direction, the change in hardness is consistent under different scanning directions. Additionally, variable thickness cladding layer deposition changes the maximum hardness distribution of the thin-walled part.

The ZrO2p/Ti-6Al-4V metal matrix composites layer, which is a novel and promising thermal barrier coating, is produced in this study by the laser melt injection (LMI) process. The microstructure evolution of the ZrO2 particle during the LMI process is studied via X-ray diffraction, electron backscattered diffraction, and scanning electron microscopy. The results show that through solid-state diffusion, the size of sub-particle in the agglomerated ZrO2 particle increases, and the morphology transforms from spherical to polyhedral. Few monoclinic ZrO2 (m-ZrO2) is found in the ZrO2 particle after the LMI. Moreover, 35% of the metastable tetragonal ZrO2 (t'-ZrO2) transforms into cubic ZrO2 (c-ZrO2). The internal stress decreases, resulting in 90% of orthorhombic (o-ZrO2) transforming into c-ZrO2. The single sub-particle comprises both t'-ZrO2 and c-ZrO2. The residual o-ZrO2 is distributed in the sub-particle boundary. The microstructure evolution of ZrO2 results in a decrease in the strength of the bonds among the sub-particles, which promotes the ZrO2 particle disintegration and improves the thermal resistance of the coating.

In this study, a fiber laser-MAG hybrid welding technology is adopted under the condition of a 10 kW laser output power. A single pass is performed with high efficiency through the welding of an 18 mm-thick EH36 marine high-strength steel plate, which realizes a good single-side welding and double-side forming technology without welding defects. The optimal process parameters of this test are 10 kW laser output power, 0 mm defocusing amount, 3 mm optical wire spacing, 400 A welding current, 31.1 V welding voltage, 14.2 m/min wire feeding speed, 20 mm wire extension length, 20 L/min protective gas flow, and 1.5 m/min welding speed. The microstructure and mechanical properties of the welded joints are studied using analytical testing equipments. Results show that the microstructure of the upper part of the weld (i.e., arc action zone) is characterized by pro-eutectoid ferrite growing in the columnar grain boundary in the form of side plates and strips and a small amount of granular ferrite in the columnar grain. The substructure in the columnar crystal mainly comprises lath martensite and acicular bainite, with a small amount of upper bainite. Meanwhile, the V-shaped banded structure is mainly composed of lath martensite and a small amount of acicular bainite. The weld microstructure of the lower part of the weld (laser action zone) is mainly composed of lath martensite. The structure of the welding heat-affected zone (HAZ) in the arc and laser action zones is mainly composed of lath martensite. The highest hardness of the welded joint in the arc and laser action zones appears in the HAZ. The laser action zone has the highest hardness, and then the V-shaped banded structure and the arc action zone of the weld. The average tensile strength of the welded joints at room temperature is 521 MPa, and all the tensile joints are fractured on the base metal. The positive bending test of the welded joints meets the standard requirements. The average impact energies of the weld metal, HAZ, and base metal at -20 ℃ are 57, 53, and 52 J, respectively. The mechanical properties meet the requirements of the classification society.

For single laser cladding, the temperature field of the laser cladding was obtained by numerical simulation. Ni-based laser cladding layers were prepared on the surfaces of Q235 steel substrates by laser cladding experiments. Based on the theory of material phase transition, the formation mechanism of the microstructure at different depths of the cladding layer was analyzed, and the effect of adding CeO2 and TiO2 nanoparticles on the cladding structure was studied. The results show that in the process of laser cladding, under the combined actions of laser irradiation and heat conduction, the temperature variation characteristics of the cladding layer and matrix at different depths are different. This leads to different types of phase transitions, resulting in different microstructures. The addition of CeO2 and TiO2 nanoparticles to the cladding powder can change the chemical composition and microstructure of the cladding structure by influencing the phase transition process of the material,the nucleation rate is improved, and an uniform and fine cladding layer is obtained.

CoCrTaAlY/YSZ thermal barrier coatings (TBCs) are fabricated by diode laser cladding and plasma spraying on a 1Cr13 steel substrate. The morphologies of coatings are observed by the scanning electronic microscopy, the composition distribution is analyzed through energy dispersive spectroscopy, and the phase composition is characterized by X-ray diffractometer. The results demonstrate that the phase composition of a YSZ coating comprises cubic ZrO2 (c-ZrO2), tetragonal ZrO2 (t-ZrO2), and a small amount of monoclinic ZrO2 (m-ZrO2). The bonding layer has typical rapid melting microstructure characteristics and metallurgical bonds with the substrate. The thermal shock performance and high-temperature oxidation resistance mechanism of TBCs as well as their failure behavior are investigated. The results show that the formation of Al2O3 oxide film can prevent the diffusion of oxygen. Consequently, the high-temperature oxidation resistance of TBCs is about 4.1 times that of the substrate (the cumulative oxidation weight gain of the YSZ coating is only 0.08 g·cm-2). The YSZ coating appears to crack for the first time after it undergoes 20 thermal shocks at 900 ℃. The cracks gradually become larger as the number of thermal shocks increases, and the coating breaks completely after 30 thermal shocks.

In this study, a time-resolved laser photometer was applied to measure the real-time variations in transmission, reflection, and scattering during the nanosecond laser irradiation of bulk fused silica. The time-resolved process of multi-pulse accumulative damage can be obtained via the multiple dynamic measurements in a single region till the damage occurs. The results show that the transmission considerably decreases during the pulse irradiation process prior to the occurrence of damage, and the backward reflectivity simultaneously increases, even up to 70%. The increase in the backward reflectivity is almost equal to the decrease in the transmission. The statistical analysis results show that as long as there exists backward reflection during multi-pulse irradiation, damage can occur. Stimulated Brillouin scattering promotes the multi-pulse-induced damage in bulk fused silica.

An extended ptychographical iterative engine (ePIE)-based method is proposed to accurately measure the transmitting wave-front of an imaging lens. The laser beam exiting the imaging lens is illuminated on a diffraction object fixed on a two-dimensional scanning stage, and the diffraction pattern is formed on the subsequent detector. The scanning stage transversely scans and records the diffraction pattern formed by the diffraction object at each position. The complex amplitude of the laser field incident on the diffraction object is faithfully reconstructed from the recorded diffraction pattern using the proposed ePIE algorithm, and the wave-front of the transmitted laser on the rear surface of the lens is retrieved using the Fresnel equations. Additionally, the wave-front illuminated on the lens can be reconstructed by repeating the above mentioned procedures after the lens is removed. Then, the transmitting wave-front of the lens is obtained by subtracting the illuminated wave-front from the exiting wave-front. The proposed method has several advantages including high accuracy, simple structure, and low cost.

Extraction and classification of road markings are two key technologies to be solved in the construction of an intelligent city and urgent technical problems that must be solved for intelligent driving. Therefore, herein, we propose a method of automatic extraction and classification for road markings based on deep learning. First, the ground point clouds are extracted through the moving-window method combined with the topological relations of adjacent scanning lines, and then the intensity images are generated. Automatic road-marking extraction and classification are realized based on the deep learning method. Road-marking vectorization is performed using the KD tree clustering algorithm and the vectorization scheme. The proposed method is analyzed based on the obtained experimental data. Results show that the precision and Fscore of the automatic road-marking extraction and classification reach 92.59% and 90.15%, respectively, proving the feasibility and accuracy of this method. Thus, the proposed method provides a new idea for automatic road-marking extraction and improves its accuracy, efficiency, and intelligent degree of road-marking acquisition and classification.

We describe an optical switch based on the stepper motor, which can be used to the pulsed atomic clocks. The switch consists of a two-phase stepper motor with 6 mm diameter and blades with different shapes to switch on and off the light. A universal stepper motor driver chip (TMC260) and a microcontroller (STC12C5A60S2) are used to control the rotation of the motors. The control system is compact. One microcontroller can be used to control multi-motors. The experimental results show that the extinction ratio higher than 100 dB is reached and the optical switches can work normally for a long term.

In order to measure the refractive index of transparent plate, an improved method based on the Michelson principle is proposed. Using the spatial coherence of low-coherent light sources and distance measurement tools, the distance between optical intervals can be accurately obtained. The optical distances before and after placing the sample and after rotating the sample at a certain angle are measured, respectively. Hence, the refractive index of the optical glass plate can be calculated by using the law of refraction. An iterative algorithm is proposed to avoid directly solving the quaternary equation of one variable and realize fast calculation of the refractive index. By analyzing the measurement errors of distance, angle, and parallelism of the sample, it is found that the refractive index measurement error of the proposed method is better than 5×10-5. The comparison result with the V-prism refractive index measurement method verifies the correctness of the proposed method.

In microscopic imaging, dual-camera dynamic phase imaging based on the transport of intensity equation (TIE) is an effective method for the quantitative observation of phase imaging of living cells. However, camera installation errors cause the difference in field-of-views of two cameras. Consequently, the phase obtained using TIE is inaccurate. This study proposes a correction method based on checkerboard calibration to eliminate the mismatch with the sub-pixel aligning accuracy. The feasibility and accuracy of the proposed method are verified by quantitatively imaging measurement for a standard microlens array. The dynamic phase imaging of the living Haematococcus pluvialis cells is successfully realized, indicating that the method has the potential for wide applications in the field of dynamic bio-microscopy imaging.

This study proposes a new nonlinear laser-limiting method based on a one-dimensional photonic crystal with double defects. Further, the variation in the center wavelength of the transmission spectrum of a photonic crystal with the refractive index of the double defect layer is studied. The laser-limiting structures of nonlinear photonic crystals operating at 532 nm and 1064 nm are designed using the proposed method, and the high transmission of weak light and high blocking of strong light are achieved. The designed laser-limiting structure, (AB)6CAC(AB)6, is an one-dimensional photonic crystal with double defects. The laser-limiting structure used for 532 nm laser employs three types of media (A, B, and C), namely diamond, SrF2, and CS3-68 glass, respectively. The optical transmittance of this laser-limiting structure for weak light is 86.4%, and that for strong light is 0.02%. In contrast, the laser-limiting structure used for 1064 nm laser employs three types of media (A, B, and C), namely diamond, CeF3, and CdTe, respectively. The optical transmittance for weak light is 79.8% and that for strong light is 0.3%.

The passively Q-switched mode-locked (QML) operation of a Tm∶Lu3Al5O12 laser is experimentally demonstrated by employing the reflective MoS2 as a saturable absorber mirror. An absorbed pump threshold of 525 mW with a 3% output mirror is achieved using a tunable Ti-doped sapphire laser as the pumping source and a low-threshold cavity design. Further, a stable QML operation state is obtained when the absorbed pump power is 1743 mW. When the maximum pump power is 3.1 W, the Q-switched mode-locked output power is 306 mW, the slope efficiency is 14.3%, the central wavelength is 2023 nm, the repetition rate is 106.4 MHz, and the maximum single pulse energy is 2.88 nJ. Furthermore, the modulation depth is observed to be close to 100%. The results show that the reflective MoS2 saturable absorber has a potential application in 2 μm laser mode-locked.

A coupling nonlinear dynamic system based on semiconductor lasers with phase conjugation and cross-phase conjugation feedback is presented. The principles of frequency detuning and frequency enhancement are analyzed, and four phase conjugation feedback schemes for frequency enhancement of two chaotic lasers are studied. It is found that the chaotic spread frequency effect of the laser can be increased to 4 times when the phase conjugation feedback is applied to a single laser. When the chaotic frequencies of two coupled lasers are increased with phase conjugation double-feedback, it is found that the frequencies of chaotic oscillation are obviously increased to more than 5 times and spectra are obviously broadened. When the cross-phase conjugation feedback is operated on a laser, the chaotic oscillation frequency can be increased to 4.4 times. When the cross-phase conjugation feedback is operated on two lasers, the chaotic oscillation frequencies of the two lasers are increased significantly, which can be increased to 4 times or 6 times, and the spectra are greatly broadened. In addition, a method for increasing the chaotic oscillation frequency is proposed based on phase conjugation double-cross reverse feedback. Results show that the chaotic oscillation frequencies of the two lasers can increase to 4.2 times or 5.9 times with the increasing feedback level, and the spectra are effectively widened.

The infrared laser occultation (LIO) technique based on the low earth orbit satellite network can perform an active detection for vertical profiles of greenhouse gases in the earth's atmospheric, thereby providing a new method for global greenhouse gas concentration profile measurement. In this paper, the principle of the concentration profile measurement of the LIO technique is introduced. The influence of the operation wavelength on the detection accuracy of the most important greenhouse gas CO2 is simulated by establishing the LIO signal link model. Subsequently, the detection wavelengths for CO2 are optimized based on the simulation results with the minimum error. Additionally, the detection performance of the LIO technique is analyzed using the selected wavelengths. Finally, the wavenumbers of 4771.6215 cm-1 and 4772.0240 cm-1 available for the CO2 concentration profile detection are selected. The selected wavelengths can achieve a vertical resolution of 0.6-1.4 km in the altitude range of 5-35 km. The relative random error of profile detection is lower than 0.8%. The minimum relative random error (0.229%) appears at 10 km. The research results can provide an important reference for the design of a prototype of spaceborne LIO atmospheric detection system.

An experimental setup of ghost imaging via sparsity constraints (GISC) for a rough surface target is designed, and the influences of both the numerical aperture of receiving system and rough target size on imaging performance of GISC are investigated and analyzed by using this setup. The results demonstrate that the imaging quality of GISC for the rough surface target is positive in relation to both parameters. This research could be considered as an instructive role for the optical system design of a GISC system.

An improved dark channel dehazing algorithm is proposed to maintain the contrast constraints of the bright and dark areas of an image. According to this algorithm, the original image is first divided into light and dark two areas and the corresponding contrast ratio is calculated. Then, the dark channel dehazing algorithm based on median filtering is used to process the dark area of the image. Finally, the double histogram equalization algorithm with accurate brightness control is used to enhance the brighter area of the image with the constraint that the regional contrast constant is maximized. The results show that compared with that processed by the correlation dehazing algorithm, the final image processed by the proposed algorithm can be significantly improved in terms of information entropy, average gradient and standard deviation of brightness. The proposed algorithm can further highlight the details of the image covered by a hazy environment.

A laser ranging system based on high-speed pulse modulation and echo sampling technology is developed. Using the high-sensitivity multi-pixel photon counter with the characteristic of multi-echo photon signal accumulative output, the photoelectric signal conversion is realized. By means of the high-speed signal acquisition, the full waveforms of the echo signals are obtained. In addition, the precise arriving time of the echo signal is achieved through the accumulation of the echo signal waveforms. Finally, the high-accuracy laser ranging is realized. The results of the theoretical analysis and the experiments show that the designed laser ranging system can realize long range target detection as well as short range laser ranging with high precision. Meanwhile, the dynamic range is up to 107 and the ranging accuracy reaches 0.6 mm.

Laser-induced breakdown spectroscopy (LIBS) was applied to detect the copper and manganese concentrations in an aqueous solution using chelate resin as the solid-phase support. Cu I 324.75 nm and Mn II 257.61 nm were selected as the analysis lines. The parameters, such as the laser energy, delay time, laser focus position, sample solution flow rate, and pH of the sample solution, were investigated. Further, the calibration curves of Cu and Mn were established under optimal experimental parameters. The detection limits of Cu and Mn were 0.03 and 0.098 mg·L-1, respectively. Furthermore, the proposed method was used to obtain the natural water samples, and the recoveries of Cu and Mn were 93.88%-108.09% and 91.99%-103.88%, respectively. The proposed method demonstrates high detection sensitivity, can be applied to natural water, and is promising for the detection of heavy metals in water environments.

In this study, the effect of quantum dot (QD) sensitization on the luminescent properties of GaAs substrates is investigated by preparing CdSe quantum dots via the chemical deposition method and depositing the quantum dots on the GaAs substrates for sensitization. X-ray diffraction is used to confirm the phase, the QD morphology is characterized via scanning electron microscopy, and the sensitized GaAs substrates are compared with the unsensitized ones through fluorescence spectroscopy. Results show that the prepared CdSe quantum dots are uniform in size (approximately 20 nm) and uniformly adhere to the GaAs substrates. CdSe QD/GaAs forms a type-II band structure. Moreover, quantum dot sensitization increases the carrier concentration on the GaAs substrate surface. The source of each luminescence peak is analyzed via fluorescence spectroscopy. Results illustrate that the band-edge luminescence of the sensitized GaAs substrate is 2.25 times higher than that of the unsensitized GaAs substrate. Furthermore, the defect luminescence of the sensitized GaAs substrate is three times higher than that of the unsensitized GaAs substrate.