Photothermal therapy is a non-invasive, targeted, and new technology, but the existing photothermal therapy technology cannot monitor the temperature distribution of the target area in real time, and the open-loop laser control method not only increases the difficulty of treatment but also causes irreversible damage to normal tissues around patient''s lesion. This paper proposes a photothermal therapy method based on precise control of photoacoustic temperature. The proposed temperature imaging algorithm was studied, the concept of photoacoustic temperature sensitivity factor was proposed and a closed-loop temperature control algorithm was designed based on the factor. Finally, a new photothermal treatment system was designed based on precise control of photoacoustic temperature, and phantom experiments were conducted. The experimental results show that the photothermal therapy method based on the precise control of photoacoustic temperature can realize the non-contact accurate measurement and control function of the target zone temperature. The system adjustment time is within 10 s and the temperature control steady-state error is within 0.7 ℃. Additionally, the results show that the photothermal therapy method based on the precise control of photoacoustic temperature can be used as a more accurate and efficient auxiliary method in the field of photothermal therapy.

The resolution and imaging quality of super-resolution fluorescence imaging significantly depend on the number of fluorescent molecular photons collected during the experiment, as well as the background noise. To obtain fast super-resolution fluorescence microscopy imaging under low photon count and high background light conditions, the proposed convolutional neural network is employed to restore the signal with extremely low signal-to-noise ratio (SNR) and combined with the reconstruction network to perform super-resolution imaging. The results show that the fluorescence signal can be effectively recovered under the condition of low signal-to-noise ratio, the peak signal-to-noise ratio can reach 27 dB, which is significantly better than the other two algorithms. The proposed method can also cooperate with Deep-STORM reconstruction network to obtain fast super-resolution imaging under low SNR conditions. The normalized mean square error of the reconstructed result is 7.5%, and the resolution is significantly improved compared to the other similar algorithms. Additionally, the reconstruction results under experimental conditions verify the ability of the proposed method and provide a feasible solution for fast super-resolution fluorescence imaging under weak signals.

Based on the theoretical model of ytterbium (Yb 3+)-doped fiber amplifier, the effect of the bend radius of Yb 3+ fiber on the mode transmission loss and dependence of optical-optical efficiency on the fiber length were analyzed. By employing the characteristics of the Yb 3+ fiber used in the experiment, the bend radius and fiber length were optimized. A master oscillation power amplification configuration was used. This configuration had a seed laser source with 170 W power, beam quality M2x=1.10, M2y=1.05, and a power amplifier with homemade 30/600 μm Yb 3+ fiber as the gain fiber. Dual-end pumping was adopted. We obtained a laser beam with an output power of 10.14 kW, a central wavelength of 1070.36 nm, and a 3 dB bandwidth of 5.32 nm. The beam quality of the output laser was M2x=3.12, M2y=3.18. In the amplification stage, the maximum optical-optical efficiency was 87.9%, and the slope efficiency reached up to 89.2%. The signal-to-noise ratio of the output laser was more than 45 dB.

In order to study the possibility of the HAP-QD conjugate of hydroxyapatite (HAP) nanoparticles and cadmium selenide quantum dots (CdSe QD) as a biological nano-temperature probe, HAP nanoparticles are chemically coupled with CdSe QD to obtain HAP-QD conjugate, and further study the temperature characteristics of HAP-QD fluorescence spectrum. First, the surface of HAP is modified by silane coupling agent KH550. Then, under the action of coupling activator, the CdSe QD with a carboxyl group modified on the surface and HAP with an amino group modified on the surface are covalently coupled to obtain a HAP-QD conjugate. Finally, the fluorescence spectra of CdSe QD and HAP-QD are measured at the temperature range of 298--318 K. The experimental results show that the fluorescence peak position of HAP-QD demonstrates a redshift and has a good linear relationship with the increase of temperature.

Based on the nearly-ballistic optimization method, a high performance uni-traveling-carrier photodiode (UTC-PD) design scheme is proposed in this paper. The UTC-PD prepared by this scheme has high response speed, high responsivity, and large saturation output, and can alleviate the load voltage swing effect. The designed novel photodiode uses a partially depleted absorption layer with gradient doping. A thin p-type doped charge layer is inserted at the bottom of the collection layer. The internal electric field of the device is optimized to make the photogenerated electrons drift at the overshoot speed, reduce the electron transit time, make the device have high bias voltage operation ability, and therefore increase the 3 dB bandwidth and improve the saturation performance. Simulation results show that under the condition of high reverse bias voltage of 8 V, the device with an active area of 16 μm 2 can obtain a 3 dB bandwidth exceeding 86 GHz with a responsivity of 0.17 A/W.

In a practical optical fiber perimeter security system, not only the discrimination of multiple events but also the comprehensive probability evaluation of these events is required. Therefore, this paper proposes a recognition scheme combining autoregressive moving average (ARMA) modeling with Sigmoid probability fitting. In event discrimination, both the ARMA coefficients and the zero-crossing rate of an optical fiber vibration signal are incorporated into a feature vector, which is then fed into a support vector machine (SVM) to recognize six types of common intrusion events: climbing, knocking, waggling, cutting, kicking, and crashing. In comprehensive probability evaluation, the SVM training pattern outputs are used to fit the parameters of a Sigmoid function. Then, the SVM outputs of the test patterns are substituted into this fitted Sigmoid model to yield the expected result. Field experiments reveal that the average recognition rate of six intrusion events by the proposed scheme reaches 87.14%. Moreover, the occurrence probabilities of all intrusion events can be provided as references, thereby presenting vast potential for future applications.

We demonstrate a dual-output ultrashort pulse fiber laser with their repetition rate precisely locked. This laser source employs a mode-locked picosecond laser capable of delivering near transform-limited pulses with 21 ps duration at a repetition rate of 40 MHz. After the seed pulse is split 1∶1, it is injected into the femtosecond and picosecond pulse amplification links respectively. By effectively managing the nonlinearity and dispersion in the pulse amplification process, the synchronous output of broadband spectral femtosecond pulse and narrowband spectral picosecond pulse is realized. In the path of femtosecond pulses, a length of 50 m polarization-maintaining single-mode fiber is used to promote the spectral broadening of amplified pulses, and its spectral width is broadened to 6.12 nm owing to the effect of self-phase modulation. Then, a pair of bulk gratings is applied to de-chirp the pulse to 483 fs duration with 210 mW average power. For the other optical path, the seed pulses are firstly pre-amplified and then selected to 10 MHz repetition rate. The 200/40 photonic crystal fiber acts as the gain fiber in main amplifier to further boost the pulses, generating 25 ps pulse duration with 1.4 μJ energy and 0.86 nm spectral width. In addition, the repetition rate long-term stabilization is realized by the combination of piezoelectric translator for precise control and stepping motor for range control. When laser system warms up, the peak-to-peak fluctuation of pulse repetition rate is less than 3 mHz within 8 h, and the corresponding standard deviation is calculated to be 0.31 mHz.

The stability of laser output power and beam pointing stability of the long optical path transmission in high-power laser devices have strict requirements, which puts high requirements on the stability of support mirror mount to maintain the position of the optical components. In order to maintain the beam collimation, the support structure must take into account both adjustability and structure stability, whereas adjustability will introduce instability. This paper proposed a structural improvement design for the commonly used adjustment structure in adjustable support mirror mount. By adding a precise sliding fit which plays a guiding role alone, the function decoupling of the thread matching of the guide and transmission coupling in the traditional adjusting structure is realized, which reduces the influence of large radial clearance on the guiding accuracy in the screw fit, improves the stability of the mirror mount, and builds a stability comparison test device. This device can be used to test the stability of different optical mirror mounts in the same optical path. Experimental results show that the improved adjustment structure could improve the stability of the overall support mount.

A phase chaos synchronization of semiconductor lasers with open-loop unidirectional coupling is studied. The phase time series of chaotic laser field is extracted using a Hilbert transform, and the phase synchronization characteristic is analyzed by a cross correlation coefficient and synchronization error. The results of the experiment show that the master laser and slave laser can attain a phase chaos synchronization with a synchronization coefficient above 0.95 at an injection strength exceeding 0.80 and its frequency detuning from -11 GHz to 4 GHz. The results also show that phase chaos synchronization has a wider parameter range than intensity chaos synchronization. According to the average phase difference, the phase-locking phenomenon is also observed during the experiment.

The causes and characteristics of the intracavity aberrations in unstable thin-disk laser are introduced. And an active correction technique is proposed to correct the aberration in the cavity by the combination of defocused and two-dimensional(2D)deformation mirrors. Based on the simulation and optimization design, the dynamic range of the defocus correction deformation mirror can reaches to 18.52 μm (peak-valley value). The static surface of the 2D mirror is less than 0.04 μm (root mean square error), the single driver dynamic range greater than 6 μm (peak-valley value), and the coupling coefficient is in the range of 30% to 35%. These two kinds of deformable mirrors are placed in the laser cavity for active closed-loop correction. The beam quality was improved to 19.5 after defocusing correction, and then improved to 6.5 after 2D deformable mirror correction. The wavefront aberration is reduced from 1.504 μm (root mean square error) to 0.185 μm (root mean square error). The beam quality increased by 3 times and the root mean square error increased by 8.1 times. Experimental results show that the combined correction mode can effectively improve the intracavity aberration in unstable thin-film laser, and its technical route is feasible.

To solve the problems of the use and protection of existing deck anti-skid composite coatings under special service conditions such as high-temperature and high-speed air erosion, we prepared a 316L stainless steel corrosion-resistant bottom layer and 316L+(ZrO2-8%Y2O3) anti-skid top layer on a Q235 carbon steel surface using the laser cladding technology. Corrosion electrochemical analysis was carried out to investigate the corrosion electrochemical behavior of the coatings in a marine environment. Furthermore, the microstructure and the internal structure of the coatings were characterized via the modern analytical testing techniques, including X-ray diffraction and scanning electron microscopy. At different temperatures (200 ℃, 400 ℃, and 1000 ℃), the heat resistance and microstructures of the coatings were compared. The results show that the novel Fe-based composite coating exhibits good corrosion resistance, which is two orders of magnitude higher than that of the carbon steel matrix. At the high-temperature condition of 1000 ℃, there was no obvious peeling and cracks on the surface of the Fe-based coating, indicating good high-temperature resistance.

Atmospheric pressure plasma polishing (APPP), as a noncontact chemical etching processing method, exhibits advantages of high efficiency, low cost, and high precision. Therefore, it can be used as an effective method to process silicon carbide. Based on the APPP gas discharge theory and tip electric field distortion effect, the effect of the APPP electrode structure on the plasma discharge stability and removal function is analyzed herein. Furthermore, the optimal electrode tip radius for APPP to process SiC is theoretically derived, finally verifying the optimal radius experimentally. After selecting the electrode, we systematically analyze the removal function characteristics of APPP in etching SiC under different processing parameters. By optimizing the electrode structure and process parameters, the pressureless sintered silicon carbide (S-Si) with a diameter of 50 mm, an initial surface profile error peak-valley value (PV) of 475.846 nm, and initial surface profile error root-mean-square (RMS) of 124.771 nm was processed. After processing for 21 min, the PV and RMS values of the S-SiC are reduced to 103.510 nm and 12.148 nm, respectively, and the RMS convergence rate is 90.26%. Experiments reveal that processing SiC using APP is more efficient than most traditional processing methods.

Laser stir welding is used herein to perform butt welding of 7075 aluminum alloy and carbon fiber reinforced thermoplastic (CFRTP), and the effect of the welding process parameters on the joint strength is analyzed. The mechanical properties of the welded joint are tested, and the factors affecting the joint strength and the failure mode of the joint are analyzed. Results show that the welding speed has the greatest influence on the joint strength, followed by the defocusing amount, laser power, stirring amplitude, stirring frequency, and clamp pressure. Under optimal parameters, the joint strength is 11.7 MPa. In this case, the fracture of the joint occurs in the surface layer of CFRTP, and the failure mode of the joint is the tearing of the CFRTP matrix. The temperature change law of the joint during the welding is measured, and the strength of the joint is reduced if the temperature is extremely high or low. Proper welding speed can prolong the high temperature time of the joint welding, increasing the joint strength.

The precision machining and assembly requirements of poly(p-phenylene-benzobisoxazole) (PBO) fiber-reinforced composites cannot be satisfied using direct integral forming or traditional machining methods. First, we cut PBO fiber-reinforced compositions using different picosecond lasers (with wavelengths of 355 nm and 1030 nm), apply a progressively downshifted focus, and implement multi-pass scanning strategy. The cross-section morphologies of the processed samples were observed using scanning electron microscopy, and the mechanisms of material removal and thermal damage of the materials were analyzed. Finally, the cutting quality and efficiency were related to the laser parameters (laser power, scanning speed and direction, and pulse repetition rate). The UV picosecond laser achieved “cold processing” and a photochemical effect with high cutting quality. The downshift of laser focus with the machining process effectively improved the machining quality and consistency of the material cutting surface. The high-quality and efficient material processing can be achieved with laser power of 8 W, repetition rate of 400 kHz and scanning speed of 1000 mm/s.

This study investigates the effects of an external alternating electromagnetic field on the joint formation, ferrite-austenite microstructure, mechanical properties, and corrosion resistance of SUS316L austenite stainless steel narrow-gap laser hot-wire feeding welded joint. The experimental results show that the controlled melting of the filler wire in a transverse direction is achieved by the alternating electromagnetic field. The joints with wider width, shallower penetration and highly symmetric weld are obtained, in addition, non-fusion and pore defects in the joints are also suppressed. The external alternating electromagnetic field introduces vibration energy into the weld pool, thereby changing the original natural convection mode of the weld pool and promoting a high-temperature liquid metal flow from the weld center to the groove sidewall. The stirring effect of the molten pool makes the temperature uniform, decreases the temperature gradient of the molten pool, inhibits the growth of coarser austenite columnar crystals, and increases the grain orientation diversity. The electromagnetic field-assisted welds have small grain size and dendritic spacing as well as a complex dendrite morphology. In summary, the joint tensile and electrochemical corrosion tests show that the electromagnetic field-assisted SUS316L stainless steel narrow-gap welded joint has good mechanical properties and corrosion resistance.

A conventional rolled (R) GH4169 sheet and a selective laser melting (SLM) additive-manufactured (3D) GH4169 sheet were welded to comparatively investigate the microstructure and mechanical properties of the three (R/3D, R/R, and 3D/3D) welded joints. Optical microscopy, scanning electron microscopy, and energy-dispersive spectrometry were used to characterize the microstructure of the butt joints; microhardness and tensile tests were also performed on the butt joints. The test results show that the microstructure of the fusion zone is mainly transformed from cell crystals to dendrites or columnar crystals and a large number of δ phases and laves phases are formed in the intergranular and intragranular regions. The grain size and precipitated phase size of the R/3D GH4169 joint, R/R GH4169 joint, and 3D/3D GH4169 joint decrease in sequence, the average microhardness of the fusion zone increases successively (250 HV, 261 HV, and 274 HV, respectively), and the tensile strength of the joints increases successively (768 MPa, 799 MPa, and 985 MPa, respectively). The fracture mode of the R/3D GH4169 and R/R GH4169 joints is mainly ductile fracture, whereas the fracture mode of the 3D/3D GH4169 joint is brittle fracture.

Glass was coated with copper films of different thicknesses by the vacuum evaporation method to realize the packaging technology for circuit manufacturing directly on glass substrate. Transient temperature and stress fields during welding of copper-plated glass were calculated using the ANSYS software. Welding experiments were conducted using a nanosecond ultraviolet laser, and the morphology and mechanical properties of welded joints were observed and tested. Theoretical calculations show that when the welding current intensity is 27 A, the average temperature of the copper film of the welding sample is approximately 3000 ℃, and the gasification speed of the copper film is slow; therefore, the welding effect is better. Thermal stresses are concentrated in the copper film whereas the thermal stress of glass is less than its theoretical strength. When the welding speed is 70 mm/s, the thermal stresses are the least. A copper film of thickness of 80 nm gives the highest welding sample tensile strength of 14.34 MPa. The optimal parameters of the laser welding process are the welding current intensity of 27 A, welding speed of 70 mm/s, and copper film thickness of 80 nm.

Ti-6Al-2Mo-2Sn-2Zr-2Cr-2V titanium alloy is prepared using a coaxial powder feeding laser deposition manufacturing process. The microstructures of the alloy in deposited and heat-treated state are studied, and the fatigue properties of the heat-treated alloy are evaluated after heat treatment. The evolution law of microstructure before and after heat treatment is analyzed, and the effects of microstructure and defects on fatigue properties are discussed. Results show that the microstructure of the deposited alloy is composed of thick primary β-columnar crystals, and the interior of the grain is composed of thin lamella α and intergranular β-phases. The volume fraction of the α-phase is significantly more than that of the β-phase. After solution and aging in the (α+β) phase region, the microstructure is still composed of coarse primary columnar crystals, the intracrystalline α-phase coarsens, and the β-phase volume fraction evidently increases. Compared with Ti-6Al-4V alloy samples prepared with the same process, the fatigue performance of the heat-treated experimental alloys is higher in the high-stress zone but lower in the low-stress zone. The difference in alloy element content, phase composition, and microstructure were the main factors affecting the fatigue performance of the deposited and heat-treated alloys. Fracture analysis shows that most of the nucleation sites of the fatigue source are located at the strip-shaped non-fusion defects and the porosity defects, and the larger the diameter of the defects, the closer to the surface, the more obvious the stress concentration, and the lower the fatigue life.

A fiber laser with a wavelength of 1064 nm was used for laser cleaning of the rusted layer on Q345 steel surface, and the effect of laser scanning speed on the cleaning quality was studied. The results show that when the scanning speed is smaller than 1000 mm·s -1, the laser significantly damages the substrate; when the scanning speed reaches 5000 mm·s -1, some rust remains on the material''s surface; when the scanning speed is 3000 mm·s -1, the cleaning effect is better and the substrate will not be damaged. As the speed increases from 1000 mm·s -1 to 6000 mm·s -1, the Fe content on the Q345 steel surface after cleaning shows a tendency of increasing firstly and then decreasing, while the O content decreases firstly and then increases. When the scanning speed is 3000 mm·s -1, the Fe element content on the Q345 steel surface reaches a peak of about 90%, the O element content reaches a valley value of about 7%, the compounds of Fe and O are also less and the surface roughness (Ra≈6.9 μm) of the steel is also low. Good laser cleaning effect can be obtained by adjusting the scanning speed appropriately. After laser cleaning, the electrochemical corrosion performance of Q345 steel surface can be enhanced.

Alexandrite is an excellent broadband tunable laser crystal with many advantages, such as long fluorescence lifetime, high saturation energy density, wide absorption bandwidth, and excellent thermodynamic properties. The unique absorption band of alexandrite crystals shows that besides flash lamp, many visible light sources such as the blue laser diode (LD), green laser, yellow laser, and red LD can be used as pump sources. Among them, the alexandrite laser based on the mature high-power red LD pump source has the advantages of high efficiency and small volume, and has gradually become a hot topic in the field of solid-state laser. Using two fiber-coupled 638 nm high-power LDs as the pump source, a double-ended polarization pumping structure is used to pump the alexandrite crystal to achieve a visible light waveband laser output with a center wavelength of 760 nm and a power of 10.5 W. The optical-to-optical conversion efficiency is 20%. This is currently the highest output power realized by red-diode-pumped alexandrite crystals in domestic researches.

To enhance the performance of cerium oxide polishing slurry and improve the polishing efficiency of Nd-glass without destroying the surface quality of Nd-glass, anionic surfactant Lamepon A was chosen to be added to the cerium oxide polishing slurry. In this work, the effects of the modified polishing slurry on the particle size of the cerium oxide polishing slurry, material removal rate of Nd-glass, and surface quality of Nd-glass after polishing were studied. The effect of pH of polishing slurry with different mass fraction of Lamepon A on the polishing rate and quality of Nd-glass were also studied. The results show that Lamepon A can inhibit the agglomeration of nanoparticles in the polishing slurry, reduce the median diameter of cerium oxide, and improve the polishing efficiency. When the mass fraction of the cerium oxide is 3%, the pH is 6.5, and mass fraction of Lamepon A is 0.30%, the material removal rate attains a maximum value of 169 nm/min; when the mass fraction of the cerium oxide is 3%, the pH is 7, the mass fraction of Lamepon A is 0.20%, the surface roughness reaches a minimum of 0.9 nm.

The Kerr and Faraday effects on the interface between a topological insulator and a Sinc-functional photonic crystal are studied by using the transfer matrix method and the equivalent medium theory. The results show that as for two kinds of linearly polarized waves, the polarization planes of their reflected waves may rotate approximately ± π2 at some frequencies. Meanwhile, the equivalent permittivity of the nearby periodic structure may change abruptly. The further investigation discloses that the law for the rotation angle of transmission wave''s polarization plane versus frequency is similar to that for the equivalent permeability of a periodic structure (BAB)n versus frequency. All the above results show that the Kerr effect and Faraday effect on the interface between a topological insulator and a functional photonic crystal are closely related to the frequency of the incident wave, the dielectric constant and the permeability of a periodic structure.

Janus membranes can realize the unidirectional transport of underwater bubbles, which is of great significance to academic research and industrial applications. In this paper, the conical microporous arrays on the upper and lower surfaces of zinc foils are prepared by nanosecond pulsed laser drilling combined with heating treatment. Additionally, the Janus zinc foils, which have the upper and lower surfaces with different roughness and microstructures, are developed through the control of laser processing parameters. Then, the unidirectional transport of underwater bubbles is studied on the prepared foils and the chemical composition of the zinc foil surface is analyzed by an energy dispersive spectrometer (EDS). The results show that the change in the wettability of the zinc foil surface is mainly attributed to the adsorption and desorption of hydrophilic hydroxyl during laser drilling and heating treatment. Observing the dynamic behavior of underwater bubbles by a high-definition industrial camera, we find that the bubbles can penetrate from the aerophobic surface to the aerophilic surface within 0.6 s, but will be blocked in the opposite direction. In addition, the increase in the pulsed laser energy within a certain range can not only increase the micropore size and the hydrophobicity of the zinc foil surface but also significantly raise the transport rate of bubbles. The transport characteristics of bubbles on the Janus zinc foils are mainly attributed to the co-action of surface micro-nano structures and chemical compositions. In a word, this study can provide a new perspective for the design of advanced materials in the fields of ultra-high-speed bubble capture, transport, collection, and gas-liquid separation.

In this paper, Tm 3+ doped and Ho 3+/ Yb 3+ co-doped tellurite-germanate glasses were prepared by the high-temperature melting method, and their mid-infrared fluorescence performances at 2 μm were studied. The results showed that as for the Tm 3+ doped tellurite-germanate glass pumped by the 808 nm laser diode, the full width at half maxium of its fluorescence at 1.81 μm was 211 nm and the corresponding emission cross-section was 6.32×10 -21 cm 2. In contrast, when the Ho 3+/ Yb 3+ co-doped tellurite-germanate glass pumped by the 980 nm laser diode, the widest fluorescence full width at half maximum of its fluorescence at 2.03 μm was 170 nm and the corresponding emission cross-section was 3.2×10 -21 cm 2. The research results demonstrate that the rare earth ions doped tellurite-germanate glass has not only the excellent physicochemical properties, but also the excellent fluorescence performances at 2 μm, which is one of the most promising gain materials for fiber lasers in the mid-infrared wavelength range.

To accurately measure the residual stress distribution, a reflective dark-field white light digital holography-based three-dimensional (3D) residual stress detection technology is proposed herein. This technology discretizes the area near the laser damage point into multiple layers in a numerical manner along the axis. The intensity of the dark-field reflected light of each layer is proportional to the axial gradient of the optical birefringence of the layer. Therefore, white-light digital holography is used to measure each layer. By measuring the reflected light intensity of each layer dark field with white light digital holography, the shear stress of each layer can be reconstructed by combining the photoelastic effect. Through the measurement of laser-damaged fused silica glass, it is verified that the proposed technique can accurately reconstruct the three-dimensional residual stress distribution of the sample, and the axial resolution can reach 10 μm. Experimental results show that the proposed technology can improve processing technology and also measure the quality of products.

In this study, an amplitude-modulation phase discrimination scheme was used. A direct digital frequency synthesizer and laser driver were used to generate a frequency-modulated laser with stable frequency. The laser was injected into the optical path to be measured, and then performed photoelectric conversion and amplification after the optical path. With regard to the phase reference signal of the frequency converter, a mixer was used to measure the phase difference between the optical path signal to be measured and the reference local oscillator signal, thereby obtaining the optical path delay information. The main contributions of this study are as follows. First, a differential detection method was proposed for the three-stage phase shift in the local oscillator signal link to optimize the phase detection point and improve the measurement accuracy. Second, a short-term two-phase point measurement mode is used in a single section to effectively reduce the measurement errors caused by the fluctuations in the light source power, light intensity in the optical path, photoelectric detection and amplification circuit gain, and phase difference drift caused by changes in temperature. Third, measurement and sampling were performed multiple times at each phase point; the phase difference was calculate based on the measured average, and the time difference was derived. The functional relationship between the measured voltage and the measured delay and the factors that affect measurement accuracy were analyzed in detail. A verification system was built, and the experimental verification was completed. The experimental results show that the scheme can obtain accuracy of 1 ps within 4-ns time delays, which can greatly improve the synchronous measurement accuracy of the existing high-power laser devices.

In order to suppress the measurement error caused by environmental vibration and realize the dynamic detection of spherical optical elements, a reflective point diffraction interference system based on micro polarizer array is proposed in this work. The interference system uses a short coherent laser source to obtain two coherent beams. The contrast of interference fringes is adjusted by adjusting the light intensity ratio of two polarized beams. Four phase-shifting interferograms are obtained by a single frame image collected by a CCD camera with integrated micro polarizer array to realize dynamic detection. The measurement results of the same concave mirror sample with the interference system and ZYGO interferometer are consistent, which verifies the accuracy of the measurement results of the interference system. On the experimental measurement platform, the vibration condition of the motor is added, and the results show that when the vibration velocity is less than 16 μm/s, more accurate surface shape measurement results can be obtained, which indicates that the anti-vibration performance of the interference system is good.

In order to solve the speckle noise residue and edge texture blur in phase image denoising, an adaptive total variation denoising method based on sine-cosine decomposition is proposed in this work. First, the original phase image is decomposed into two phase images by sine and cosine function. Then, the decomposed phase image is processed by adaptive total variation algorithm. Finally, the denoised phase image is synthesized by arctangent operation to quickly remove a large amount of speckle noise and retain the edge information of the image. The quantitative evaluation and analysis of the denoising results show that, compared with other denoising methods, the peak signal-to-noise ratio of the image obtained by this method is improved by 2.0 dB, and the structure similarity is higher. At the same time, the parameters can be adaptively selected to reduce the fluctuation of the phase image and improve the its quality.

Based on the atomic force microscope (AFM), the fluorescence microscopic imaging system and the time-correlated single photon counting (TCSPC) system, the spontaneous emission enhancement of quantum dots and the fluorescence surface plasmon polariton (SPP) propagation are studied in a coupling structure of a gold nano-sphere (AuNS) and a sliver nano-wire (AgNW). The coupling between the AuNS and the AgNW is achieved in two ways. Firstly, a mixed solution of AuNSs and quantum dots, and the solution of AgNWs are successively coated on a SiO2 substrate to look for the AuNS-AgNW coupling structures that are randomly formed. Secondly, a controlled AuNS-AgNW coupling structure is achieved by using the AFM nano-manipulation. Based on the AuNS-AgNW coupling structure with quantum dots in its nano-gap, the experimental results show that the enhancement factor of the spontaneous emission rate of the quantum dots fluorescence can be up to 611 and the propagation of the fluorescence SPP along the AgNW is also observed. COMSOL Multiphysics software is used to simulate the enhancement factor of the spontaneous emission rate of a quantum dot with different positions and polarizations near the AuNS-AgNW coupling structure. The results are compared with those of a quantum dot coupled with single AuNS and single AgNW, showing that the AuNS-AgNW coupling structure can provide a higher enhancement factor of the spontaneous emission rate. The propagation of the SPP along the AgNW excited by the point source is also calculated. The simulation results agree well with the experimental results.

In this study, line defects and point defects are introduced in a completely two-dimensional square lattice silicon. Using waveguide coupling and linear interference, a three-input all-optical AND gate based on the two-dimensional photonic crystal is proposed herein. The proposed AND gate is simulated using the plane-wave-expansion method and finite-difference time-domain method. Results show that the proposed AND gate has a contrast ratio of not less than 3.5 dB when the input-light wavelength is between 1544 nm and 1555 nm, and the response time reaches the subpicosecond level. The acceptable horizontal offset of the point defect offset dielectric column is between 0.06 μm and 0.19 μm. The proposed solution exhibits a simple structure, a wide operating-wavelength range, a fast response time, and it can realize the AND gate in the case of three inputs. The proposed AND gate has potential applications in the field of an all-optical signal processing system and an integrated optical path.

In this paper, a new optical parametric amplification scheme based on electro-optic effect is proposed. The change characteristics of gain bandwidth of potassium deuterium phosphate (DKDP) crystal are theoretically analyzed with the change of deuteration rate, and the variation characteristics of gain bandwidth of DKDP crystal with 70% and 95% deuteration rate under different electric field intensities are studied. At 885 nm central wavelength, the gain bandwidth of DKDP crystal with 70% deuteration rate can be broadened from 90 nm to 124 nm when the electric field strength of 1.67×10 5 V/m is applied. At 808 nm central wavelength, the gain bandwidth of DKDP crystal with 95% deuteration rate can be broadened from 52 nm to 68 nm when the applied electric field is 1×10 5 V/m. The results show that the linear electro-optic effect can effectively broaden the gain bandwidth of the optical parametric amplification system, and the central wavelength of the gain spectrum can be adjusted by electro-optic modulation to achieve continuous wavelength tuning. It has a great application prospect in high-energy ultrashort laser system.

The theoretical and experimental researches on the classical physical picture of magnetic resonance in a rubidium atomic magnetometer under sequential control based on a pulsed pump-probe manner are reported in this paper. The basic principle of this atomic magnetometer is that the light polarization direction will produce rotation related to the magnetic field because of the different absorption and dispersion of the left and right circularly polarized components by the polarized rubidium atoms when the linearly polarized probe beam passes through the vapor cell. A classical physical picture of two-level magnetic resonance is adopted to describe the physical process of interaction between a radio frequency field and atoms, and the specific formula is derived in the rotating coordinate system. Meanwhile, the formula of the output signal acquired by the atomic magnetometer is obtained in the laboratory coordinate system. It is pointed out that the output signals acquired by the rubidium atomic magnetometer are related to the projection of macroscopic magnetization in the direction of the probe beam. The experimental results verify the theoretical analysis. The research results are helpful to deepen the understanding of the classical physical picture of magnetic resonance as well as the basic working principle and parameter setting of atomic magnetometers under sequential control.

The micro Doppler features of a target can be used as the basis of target recognition. The detection of micro Doppler features is often affected by the vibration of lidar itself in the direction of laser beam, and it is difficult to eliminate the influence of local vibration on the measurement results. In this paper, a method of using the reference point of the target itself to suppress local interference is proposed. The local vibration and relative motion interference can be suppressed by analyzing the beat frequency signal between echo signals from the target position and reference position and the local vibration signal and by the compensation process. Experimental results show that the proposed method has a significant effect on the suppression of local vibration and target relative motion interference, and the relative compensation accuracy is less than 5%. The micro Doppler characteristics obtained after compensation can better reflect the real micro vibration of the target.

This study proposed a method for optimizing and regularizing building contours step by step to investigate the irregular problem of building contours extracted by classification in a high-resolution remote sensing image. The initial building contours were extracted and reconstructed by polygon fitting based on the initial building results extracted by the image classification and verification. The best fitting circumscribed rectangles consistent with the building axis inclination were then obtained. Subsequently, the contour lines of the building polygon and their corresponding best circumscribed rectangular boundaries were divided into equal segments. After which, the Hausdorff distances between the building polygon and rectangular boundary segments were calculated. Contour preliminary regularization and optimization were accomplished herein by replacing the building segments, whose Hausdorff distances were smaller and satisfied with the replacement condition, with the corresponding best-fitting circumscribed boundary segments. Deep optimization for a complex partial contour not well optimized in the former step was also explored. The feature corner points on the complex boundary were extracted, matched, sorted, and removed to keep the best ones based on the Shi--Tomasi algorithm. Lastly, the remaining points were connected and reconstructed to optimize the complex local contour. As a result, the edge expression degree accuracy and the extraction accuracy after the contour optimization were improved. The experimental comparison and analysis results of multiple remote sensing images show that this method is not only suitable for the contour optimization of building results extracted by different classification methods but also effectively improves the edge expression accuracy of building contours. According to the change of complex building contour details, the proposed hierarchical optimization method was more accurately adaptive than the reference contour optimization method. It also achieved a better overall optimization accuracy. In other words, the building edge accuracy and regularity can be effectively improved, and the true building shape can be more accurately reflected.

To improve the reciprocity of the system and effectively suppress the influence of backscattering noise on resonant micro-optical gyroscope (RMOG) detection accuracy, an optical switch-based RMOG is proposed. First, we analyze and test the influence of backscattering noise in the actual RMOG system; the same frequency modulation is performed on both clockwise and counterclockwise lightwave signals, which are time-division multiplexed using a 1×2 optical switch to alternate the laser output between clockwise and counterclockwise separating the signal and backscattered light in time and reducing the influence of backscattering noise on RMOG detection accuracy; furthermore, the channel crosstalk of the optical switch and the effect of switching time on backscattering noise are analyzed. The experimental results show that the optical switch can reduce the backscattering noise, and the degree of reduction is limited by the switch crosstalk. The switching time of the switch needs to be optimized for the time constant of the optical waveguide-ring resonator and the loop lock time.

Photoelectric composite cable is the lifeline of tethered unmanned aerial vehicle, which transmits power and signal. When the internal tension of the cable is too large, the internal optical fiber will break. In order to monitor the tension distribution inside the cable, it is necessary to measure the strain of the cable. When fiber Bragg grating sensor is used to measure the axial strain of the composite cable, it is found that the large-scale and rapid movement of the slender composite cable will easily cause the local bending of the cable, resulting in the splitting of the reflection peak of the reflection spectrum. Based on the theory of mechanics of materials, the reason why the reflection peak splits during the bending of composite cable is analyzed. The theoretical analysis result is verified by experimental, and an improved measurement method is proposed, which avoids the influence of viscose and internal shear force of cable on the measurement result, and effectively improves the accuracy of axial strain measurement.

In the diagnosis of combustion flow field by absorption spectra, the accuracy of absorption molecular spectral line parameters directly affects the accuracy of the measurement of flow field parameters. In this paper, the absorption spectral line parameters of water molecules used as the main probe in combustion diagnostic studies are calibrated accurately. A near-infrared diode laser with a wavelength of 1469 nm is used as the light source, and the highly sensitive calibration-free wavelength modulation technology is used. Combining with the established laboratory high temperature measuring system, we obtain the modulation absorption spectra of the selected spectral lines in the temperature range of 900--1500 K. By using the nonlinear least square L-M fitting method to fit the H2O absorption spectra, the line intensities, self-broadening coefficients, and temperature dependent coefficients of the selected spectral lines at 6807.83 cm -1 and 6808.04 cm -1 are accurately obtained. By comparing the HITRAN and HITEMP databases, we obtain that the relative deviations of line strengths are 3.91% and -5.40%, the relative deviations of self-broadening coefficients are 3.01% and -6.49%, the temperature dependence coefficients are 0.5213 and 0.4567, and the uncertainties of the experimental results of the two line strengths are 1.05% and 1.96%, respectively. The spectral parameter calibration method based on calibration-free wavelength modulation has the advantages of high detection sensitivity and spectral signal-to-noise ratio in high temperature spectral measurement, which is conductive to improve the accuracy of spectral parameter calibration, and will provide spectral line foundation for accurate inversion of combustion flow field parameters.

Three-dimensional fluorescence spectra of polycyclic aromatic hydrocarbons (PAHs) in soil are directly recorded using a fluorescence spectrophotometer. To identify the components of PAHs in soil, nonsmooth non-negative matrix factorization (nsNMF) are used. Results show that NMF can effectively extract the fluorescence spectrum signal of a single PAH from the mixture spectrum. The similarity coefficient between the analytical spectra and corresponding reference spectra obtained by nsNMF under random initial values is all above 0.824, which is higher than that of the standard NMF based on alternating non-negative least squares (NMF/ANLS). In farmland soil, the similarity coefficients of phenanthrene and anthracene between the analytical spectra and corresponding reference spectra increased from 0.758 and 0.845 (NMF/ANLS) to 0.907 and 0.913 (nsNMF), respectively. The combination of three-dimensional fluorescence spectra and nsNMF can facilitate rapid identification of components of PAHs in soil.

Emulsified oil spill is a kind of oil spill pollution form caused by the interaction between oil-spilled and sea water. This kind of morphology is different from other forms in laser-induced fluorescence (LIF) detection. Therefore, from the perspective of fluorescence spectrum, diesel oil and kerosene were used as the experimental objects to carry out the experimental study on the fluorescence characteristics of light oil emulsions. Experimental results show that the emulsification of light oil will go through different stages, and will have different effects on the fluorescence spectrum of laser irradiation emission with the constant change of oil-water ratio distribution. The comparative analysis of the spectral curves at different stages shows that when the excitation wavelength is 405 nm and the emission wavelength is 420 nm to 500 nm, the number of fluorescence peaks increases, the peaks increase or decrease, the peak ratio changes, and the fluorescence peak position shifts during the emulsification process. The changing characteristics constitute the rule of fluorescence characteristics of light oil emulsification. This regular pattern can provide some basis for LIF detection and identification of actual emulsified oil spill. Due to the difference of light oil components, the change degree under the same change trend of fluorescence characteristics will be different. In order to achieve the accurate monitoring of emulsified oil spills, it is necessary to combine with specific oil types.

A set of experimental measuring devices is developed by combining the laser ablation technique with absorption spectroscopy to obtain laser ablation absorption spectra. Alloy steel is used as the test sample, and the ground state transition (394.40 nm) of the aluminum atoms is selected as the analytical spectral line for the quantitative detection and analysis experiment of aluminum in the alloy steel samples. The experimental results reveal that the most suitable experimental conditions for the successful detection and analysis of aluminum include a laser pulse energy of 30 mJ, a detection height of 2 mm, and a sampling delay time of 8 μs. Under these optimized conditions, the high-resolution and high-sensitivity absorption spectrum signals of the aluminum atoms in the alloy steel standard samples are obtained, while the calibration curve of the aluminum content and absorption intensity are also determined. Moreover, the fitting parameters of the calibration curve are higher than 0.999, and the limit of detection is 0.066%. Thus, laser ablation absorption spectroscopy proves to be effective for the quantitative analysis of aluminum in alloy steel, while the results also indicate its great potential for the quantitative analysis of trace elements and isotopes in alloy steel and other materials.

Glass fiber reinforced composite materials are widely used in aerospace, construction, and transportation industries. However, due to the defects such as debonding and delamination during the production and using processes of composite materials, non-destructive detection is necessary to carry out. In this paper, the method combining terahertz tomography and defect characteristic waveform imaging is used to study the debonding defects of glass fiber reinforced composite materials with different depths and different areas. Aiming at the fringe interference in tomography, a phase-based fringe suppression method for terahertz tomographic images is proposed, which eliminates the fringe interference in tomography, and further improves the imaging quality. The identification of debonding defects with a distance from surface of 5 mm, a diameter of 5 mm, and a thickness of 0.05 mm is realized. This study provides a new method for processing the results obtained by reflection type terahertz tomography.