Upconversion laser has the characteristics of anti-stokes displacement, monochromatism, and high stability. It has been widely used in many fields, such as medicine, projector, data storage, laser headlamp, laser teletype visible light communication, microscope, and new generation display technology, which has gained major progress in both basic research and application exploration after more than ten years of development. But there are still problems and bottlenecks. The research status of the upconversion laser is reviewed. As for different band and different pump sources, the main progress in recent years is specifically introduced. In addition, as for this topic, the critical issues at present are commented and the future development is prospected.

As a new semiconductor material, perovskite material has the advantages of large absorption coefficient, long carrier diffusion length, low defect density, and tunable bandgap, and has wide application prospects in photovoltaic fields such as solar cells and light sources. This paper mainly discusses the achievements and research progress of perovskite as laser gain medium in the field of micro-nano laser, and summarizes the classification of different laser cavity modes. Finally, the development prospects of perovskite material micro-nano laser are prospected.

Due to the ultra-wide range of infrared transmittance spectra and extremely high linear and nonlinear refractive index of chalcogenide glasses, chalcogenide fibers have become the only optical fiber host materials for mid-infrared and far-infrared supercontinuum (SC) spectrum generation. A series of important progresses has been made in the past three years. In this paper, the latest research progress of chalcogenide glasses is reviewed from several aspects such as mid-infrared SC spectrum generation and spectrum coherence of step-index, microstructured, and tapered chalcogenide fibers,and the all-fiber SC sources.

This paper introduces and summarizes the main progress made in the research of Yb-doped rare-earth calcium oxyborate (Yb∶ReCOB) crystal lasers in recent years. It includes continuous-wave lasers, acousto-optic Q-switching, passive Q-switching with Cr 4+∶YAG, GaAs, or two-dimensional materials as saturable absorber, Saturable absorber mode-locked, Kerr-lens mode-locked, and self-frequency doubling green and yellow lasers. This type of Yb∶ReCOB crystal shows great potential for many all-solid-state laser applications with different modes of operation.

Yb-doped bulk materials are becoming an effective technical way for delivering high power ultrashort pulse lasers. They are inexpensive and easy to be processed, adjusted, and resistant to higher pulse energy, all of which make bulk-material-based ultrashort pulse laser amplifier be a hot topic. Usually, there are two kinds of configuration for amplifiers, travelling-wave (single, double-pass, four-pass) amplifiers and regenerative amplifiers. The gain media are not limited to the well-known Yb∶YAG, Yb∶KGW, and Yb∶KGW, such new candidates as Yb∶CALGO, Yb∶CaF2, Yb∶Lu2O3 and Yb∶Y2O3 are also emerging. Efforts are paid to review currently reported representative results, to show the potential application of Yb-doped bulk materials as the base for generating ultrashort pulse lasers with average power from hundreds of to thousands of watts.

Blue-green lasers have a broad application prospect in laser display, medical diagnosis, optical data storage, and underwater communication. In particular, the blue-green single-frequency laser has high coherence and can be used in fields such as high-resolution spectroscopy, atomic cooling/capture, and quantum optics, which have attracted extensive attention of scholars at home and abroad and developed rapidly. In this paper, several key technologies of realizing blue-green single-frequency lasers are introduced, such as second harmonic generation (SHG) to obtain blue-green single-frequency lasers, and directly lasing from semiconductor materials. The research status and development direction of the blue-green single-frequency laser are summarized. In addition, according to the research work of our group in the fiber-based blue-green single-frequency laser, the research progress of obtaining blue-green single-frequency lasers through SHG technology based on near-infrared shortwave single-frequency fiber laser is introduced emphatically. Simultaneously, the development of blue-green single-frequency laser technology is prospected.

Miniaturization and integration of optical devices are important trends in the development of modern optical systems. In micro-optical devices, arrayed refractive imaging micro-optical devices mainly include microlens array devices, which are widely used in imaging, metrology, beam shaping and other fields. In response to the special application requirements in the infrared band imaging, metrological measurement, laser processing and other fields, microlens array devices working in the infrared band have received extensive attention and have developed rapidly. This paper summarizes the development and preparation methods of infrared microlens array devices, including the preparation of infrared micro-optical devices with different materials and manufacturing methods, and the application of infrared micro-lens array devices in infrared band imaging, metrology, parallel processing, and beam homogenization. The challenges and opportunities of infrared microlens array devices and their manufacturing methods are also analyzed.

Combining the advantages of oxide glass and fluoride crystal, the oxyfluoride glass ceramic introduces a low phonon energy filed into stable amorphous glass, making it an excellent matric material for rare earth ions to radiate. Hence, the oxyfluoride glass ceramic has a unique and important application in the field of high-efficiency and high-power lasers. At present, researches on rare earth ion-doped oxyfluoride glass ceramics are mainly focused on their luminescent mechanism. Furthermore, using excellent materials to achieve laser output is still in its infancy. This study introduces the research progress in solid-state lasers based on rare earth ion-doped oxyfluoride glass ceramics, including fiber lasers, whispering gallery mode lasers, and random lasers. In addition, the advantages and disadvantages of rare earth ion-doped glass ceramic applied as gain medium of solid-state lasers are analyzed and discussed. The technical points of this material for solid-state lasers are summarized, and the future development direction is prospected.

Potassium tantalate niobate (KTN) electro-optic deflection devices attract much attention in recent years due to the advantages of large angle, low voltage, no inertia, and small size. The research progress of KTN crystal devices and applications at home and abroad is briefly reviewed. The basic principles of electro-optic deflection based on the space charge, composition gradient, and temperature gradient of the crystal are described. The characteristic parameters and main influencing factors of deflection properties of the devices are discussed. Several kinds of components and application examples based on KTN electro-optic deflection are introduced and the current problems and future trends are also summarized.

In this paper, we summarized the related researches of YAG ceramic lasers and sesquioxide ceramic lasers in high-power lasers, ultrafast lasers and mid infrared laser materials. By reviewing the research progress of ceramic lasers, it not only revealed great value of laser ceramic materials applied to solid-state lasers, but also discussed the problems that ceramic lasers currently faced. Finally, the future development of ceramic lasers was prospected.

Stimulated Raman scattering is an important frequency conversion method for obtaining novel wavelength laser. For an intracavity Raman laser, the fundamental light and multi-Stokes light simultaneously resonating in the laser cavity provide the possibility for outputting multi-wavelength visible laser by second-order nonlinear optical frequency conversion, which can meet the application needs for multiple wavelength laser in some fields, such as laser medical treatment, laser display, spectral imaging, and biophotonics. Vanadate crystal is an important solid Raman gain medium driven by Nd-ion laser for its excellent stimulated Raman scattering properties. In this paper, the Raman spectral characteristics of vanadate crystals and the research status of related Raman laser are briefly introduced. Then, the research progress of second harmonic and sum-frequency generation of Raman laser in recent years is summarized, and the development and application prospects of techiques for generating multiple wavelength-switchable visible laser by Raman selective frequency mixing are briefly analyzed.

Optical beam forming network has the characteristics of large bandwidth, low transmission loss, and anti-electromagnetic interference, compared with the traditional electrical beam forming network. In the case of multi-channel radio frequency signal input, the law of insertion loss of optical beam forming networks based on the dispersion fiber system is less studied. Assuming that the photon detector reaches the saturation threshold, the insertion losses of the single-channel microwave photon link and the dual-channel optical beam forming network are calculated. It is deduced that as the number of input radio frequency channels increases by multiple folds, the insertion loss of the optical beam forming network using a dispersion fiber also increases in an alike manner. A test system was set up, and verification was carried out. When the number of input radio frequency channels was 2, 4, 8, and 16, the corresponding insertion loss was -26.0 dB, -30.8 dB, -34.3 dB, and -46.0 dB, respectively.

Transfer oscillator technology based on femtosecond optical frequency comb is studied, its basic principles are introduced, and the transfer oscillator system is designed and built. The coherent transfer of optical frequency between the master laser and the slave laser is realized. The second-level frequency stability of beat note signal in the system loop reaches the order of 5×10 -19. For further evaluation, two sets of transfer oscillator systems are setup to transmit the optical frequency of the master laser to two independent slave lasers at the same time, and the phase noise introduced into the system by the beat note signal of the two slave lasers after locking is analyzed. By improving the signal-to-noise ratio of the beat note signal, optimizing signal processing, and reducing external environmental interference, the two outer beat note signals obtained from the two slave lasers have a line width of less than 30 mHz and the s-level frequency stability of optical frequency transmission reaches the order of 1.4×10 -17.

In this paper, an off-axis two-mirror system that can not only make the output beam irradiance distribution uniform, but also control the output beam wave-front and beam-expansion ratio, is designed for laser shaping. By setting two constraints and initial conditions, the iterative relationship between the adjacent sampling points on the free surface can be obtained, and all the sampling points on the whole free surface can be calculated. We use a software to verify the system, and the 16 mm×16 mm square aperture is transformed into an 80 mm×80 mm square aperture and a 120 mm×20 mm rectangular aperture; the outgoing beams are all collimated beams. The results show that the square spot uniformity is 90.74%, and the beam expansion ratio is 5; the rectangular aperture spot uniformity is 94.75%, and the beam expansion ratios in the horizontal and vertical directions are 7.5 and 1.25, respectively.

At present, the identification of toxic gases by electronic noses has a small amount of data, and the ability of neural network mapping generated by training is insufficient. In this work, the formaldehyde and methanol are used as target gases, and collected by self-made gas sensor. After filtering and smoothing the collected data, the different response values are extracted. The pseudo-random numbers are generated according to the criterion function, and the pseudo-random matrix is established to expand the effective data volume.The principal component analysis (PCA) is used to reduce the dimensionality of the eigenvalues, and the principal component score with large contribution rate is selected as the input vector of the back-propagation (BP) neural network to construct PCA-BP neural network, which is trained by using the measured eigenvalue matrix and the pseudo-random eigenvalue matrix respectively. By comparing the two networks, the recognition rate of the measured eigenvalue matrix is 92%, and the recognition rate of the pseudo-random eigenvalue matrix is 97%. The results show that the pseudo-random eigenvalue matrix can effectively improve the mapping ability of BP neural network and the accuracy of recognition.

Due to the reflection characteristics of the bright surface, the general three-dimensional shape measurement method are difficult to measure.To solve this problem,a scheme based on binocular vision and phase deflection method to measure the three-dimensional shape of bright surface is proposed. The binocular system layout uses the camera horizontal placement, and the complete screen-camera-adjustable platform measurement system is integrated into a custom frame.In order to reduce the calibration error, the Levenberg-Marquardt algorithm is used to optimize the position parameters obtained from the system calibration. The matching point search efficiency is improved by combining the uniqueness of the bright surface normal vector with the polar constraint of the camera.The traditional trigonometry method is improved to find the space points and the accuracy of the surface points of the object to be measured is improved. The experimental results verify that the proposed method has high measurement accuracy and stability.

Circular coding target has been widely used in the field of three-dimensional measurement. The center extraction accuracy of the target directly affects the measurement accuracy of the system. Aiming at the problem that the center extraction accuracy of the circular coded target is easily affected by camera angle, a method for extracting the center of the circular coded target based on radial straight line fitting of circular coding is proposed in this paper. First, the radial straight line edge of the circular coded target ring is obtained by edge extraction after image preprocessing, and sub-pixel location of the edge point is achieved by Gaussian fitting. Then, the extracted sub-pixel edge point set is mapped to a parameter space into curves, and the intersection points between these curves is thus obtained. Finally, a random sampling consistency algorithm is used to fit and map to the original coordinate space to get the center coordinate. Simulation results show that the center coordinate error extracted by this method is reduced from 1 pixel to 0.05 pixel with increase of target size and shooting angle. Experimental measurements show that the error of the center coordinate extracted by this method is kept within 1 pixel for different target sizes and shooting angles. Compared with the ellipse fitting method, the reprojection error of the camera calibration is reduced by 20%, and the calibration result is more accurate.

This paper introduces an ultra-narrow linewidth Brillouin fiber laser based on distributed feedback fiber laser. By constructing a Brillouin ring cavity structure, a distributed feedback fiber laser is used as the Brillouin pump, a 980 nm semiconductor laser is used as the pump source for the intra-cavity erbium-doped laser amplification, thereby the Brillouin laser output with ultra-narrow linewidth is achieved. The Brillouin ring cavity is about 10 meters long, and a single longitudinal mode Brillouin laser is obtained with a proper polarization control. To ensure the single longitudinal mode laser output, the power of the distributed feedback fiber laser and the 980 nm pump source should be no less than 20 mW and 50 mW, respectively. With the output power of the pump source up to 250 mW, the final Brillouin laser output power exceeds 15 mW, and the linewidth is estimated to be less than 100 Hz.

In order to study the formation process of keyhole, in the fiber laser plate scanning welding of low carbon steel, experiment was carried out by modulating laser light-out time. Experimental results show that the formation process of keyhole is extremely rapid, and the whole formation time of a keyhole is in ms level. In low-speed welding, the formation process of keyhole includes three stages: rapid increase, slow increase, and roughly stabilized stage. During high-speed welding, the formation process of keyhole only includes rapid formation stage. Further experiments show that the formation time of keyhole is not exceeding the characteristic time of laser welding and the characteristic time of laser welding decreases with the increase of welding speed, which together explain why keyhole formation only includes the rapid formation stage in high-speed welding.

A simple tunable multi-wavelength Raman fiber laser with output wavelength near 1.7 μm band is proposed and experimentally demonstrated. In this scheme, a 1550 nm band amplified spontaneous emission is used as the pump source and avoid stimulated Brillouin scattering. The dispersion shifted fiber and high nonlinear optical fiber are used as nonlinear gain to obtain the gain spectrum with peak wavelength near the 1.7 μm band, and an unpumped erbium-doped fiber is used to absorb the remaining pump light in the gain spectrum. The gain spectrum is filtered by a Sagnac loop filter. We demonstrate the tuning capacities of single-wavelength over 33.4 nm between 1652.77 nm and 1686.20 nm by adjusting the polarization controller and tunable filter on the back end of the amplified spontaneous emission. The 3 dB effective linewidth of single-wavelength laser is 0.08 nm. And by increasing the pump power and adjusting the Sagnac loop filter to achieve multi-wavelength laser output, the dual-wavelength laser can be continuously tuned between 1654.88 nm to 1664.60 nm. The side mode suppression ratios of single-wavelength and dual-wavelength lasers are greater than 45 dB.

In order to realize the laser cladding remanufacturing and repair of tractor spindle, Ni60A alloy coating was prepared by laser cladding technology on spindle material 40Cr axial surface. The effects of defocusing amount on the macromorphology, microstructure, microhardness, and wear resistance of the cladding layer were analyzed by optical microscope, microhardness tester, and friction wear tester.The results show that when the defocusing amount is 8 mm, the surface of the cladding layer is smooth and flat, and there are no defects such as pores, cracks, and slag inclusion on the bonding surface.In the middle of the cladding layer, there are fine equiaxial crystals, dendrites and columnar crystals on both sides, and planar crystal structures growing along the surface of the substrate at the bottom.The highest hardness was found in the middle of the cladding layer, and its microhardness was up to 660 HV, twice that of the substrate.Under the same wear condition, the wear weight of cladding layer is only 33% of that of matrix material.As the amount of defocusing increases, the surface roughness of cladding layer increases, the hardness non-uniformity increases, and the wear resistance decreases.

Chlorophyll-a (Chla) can intuitively reflect the degree of eutrophication of water, Chla concentration can be accurately estimated via the three-band bio-optical model because it can weaken the influence of factors such as suspended and yellow matter in case-II waters. Therefore, the approximate position of the three-band factor was determined by analyzing the spectral characteristics of the measured water body. Further, three characteristic bands and a retrieval model were established using the exhaustive method and correlation analysis. Results show that when λ1=661.63 nm, λ2=693.54 nm, and λ3=757.35 nm, the three-band factor [ Rrs-1(λ1)- Rrs-1(λ2)]Rrs(λ3) exhibits a high correlation coefficient with the Chla concentration (r=0.830). The determination coefficient, root mean square error, and mean absolute percentage error of the model are 0.859, 2.446 mg·m -3, and 32.169%, respectively, furthermore, the accuracy is better than that of the band ratio and reflection peak models. These results can provide a theoretical basis and technical support for the Chla retrieval in the lower reaches of the Minjiang River and enable band selection for the subsequent retrieval of the Chla concentration in case-II waters using the three-band factor method.

The scattering ability of light guide plate (LGP) dots directly affects the light energy utilization and dot density of backlight module, so quick selection of the best dot structure is very important for manufacturers. This paper proposed a method to evaluate the effective light guiding ability of dots by LGP dot scattering efficiency. Based on the LGP dot density file that has been mass-produced by the manufacturers, the influence of the dot inclination angle on the scattering efficiency was studied theoretically and experimentally, and the best dot structure obtained was applied to actual processing. The results show that the method can reveal the correlation among the dot scattering efficiency, the light energy utilizaiton rate, the effective light-emitting area and the dot density. An inclination angle range of 25°--60° corresponding to the maximum light energy utilization rate can be obtained. In this range, the dot scattering efficiency and inclination angle are positively correlated. By re-optimizing the LGP uniformly with dots with higher scattering efficiency, it is found that the number of dots could be reduced by 60%, the light energy utilization rate is only reduced by 2%, and the actual machining effect of LGP is consistent with the simulated effect.

In order to resolve the contradiction between high spatial resolution and the tight space of microsatellites, a coaxial ultra-compact primary and tertiary mirror integrated optical system was designed based on the aberration theory and the coaxial four-mirror optical system. The optical system was verified under the condition of a focal length of 1750 mm, an F-number of 7, and a full field of view of 1.4°, and its tolerance and signal-to-noise ratio (SNR) were analyzed. The results show that the overall length of the optical system is less than 200 mm, which is only 1/8.75 of the focal length, suggesting an ultra-compact and small blocking ratio design of the optical system. With increased blocking, the full field transfer function is better than 0.26 and the full field wave aberration is better than λ/50 at a Nyquist frequency of 78 lp/mm. The SNR is better than 24.9 when the altitude of the sun is 30° and the surface reflectivity is 0.05. The system structure is simple and compact, and the imaging quality is good, which has certain reference for the design of high-resolution optical systems for microsatellite.

One of the difficult problems in optical manufacturing is to process and test large aperture and high-order aspheric surface. The spherical aberration coefficient of a high-order aspheric concave mirror with an effective aperture of 900 mm and a radius of curvature of 2580 mm was derived. Based on third-order aberration theory, the normal aberration of the high-order aspheric surface was compensated, and the initial structure of the compensation system was solved. Compensation systems based on spherical wave and plane wave were designed respectively, and the high-order aspheric concave mirrors were polished. The accuracy of the surface shape measured by four-dimensional interferometer is 0.022λ which meets the actual measurement requirements.

Herein, to achieve high-performance mobile phone lens optical system with a large view field, low cost, and high resolution, two single-center and ultra-wide-angle optical systems of mobile phone lens with different filtering methods are designed based on ZEMAX software, which are matched with a curved sensor. The two optical systems comprise four concentric plastic lenses, a curved surface filter, or an IR-CUT film with the system F-number of 1.8, view field of 130°, and focal and total lengths of the system of 2.64 mm and 4.1 mm, respectively. The modulation transfer function (MTF) value of the central view field is greater than 0.5 and 0.3 at 200- and 400-lp/mm Nyquist frequencies, respectively. The MTF value of less than 0.7 view field is greater than 0.2 at 400-lp/mm Nyquist frequency. The relative illumination of full view field is greater than 0.42. The maximum RMS radius is less than 3.75 μm, which satisfies the requirements of mobile phone lens imaging. The design of an ultra-wide-angle, short focus, and compact optical system is accomplished with high machinability and high imaging quality.

Aiming at the problem of uneven current distribution in GaN-based LED chip, the traditional electrode structure is optimized. By establishing a three-dimensional simulation model based on finite element analysis software COMSOL, the current distribution in the active layer of chip electrode with optimized structure and traditional structure is simulated respectively. The results show that the current distribution in the chip with optimized structure is more uniform. Then, LED chips of various structures are prepared and tested for photoelectric performance. Experimental results show that changing the shape of the N electrode to a fan-shaped structure can improve the light output efficiency of the LED. When the input current is 20 mA, the output light power of the LED chip is 31.84 mW, and the light extraction efficiency is 52.03%, which is 6.14% higher than that of the conventional LED chip.

In this study, high quality 0.3BaSrTiO3-0.7NdAlO3 microwave dielectric ceramics are prepared using solid state reaction method. Their absorption characteristics in the terahertz range are investigated using terahertz time-domain spectroscopy. It is observed that the absorption coefficient could be modulated using the external optical pump at the 18 ℃(291 K), and the tunability could reach up to 34.46% at 0.55 THz. By fitting the dielectric constant and light power of 0.3BaSrTiO3-0.7NdAlO3 ceramics at 0.45 THz and 0.55 THz, the anharmonic parameter α are observed to be 1.273×10 -8 and 1.823×10 -8, respectively. In addition, the micro-mechanism of absorption coefficient modulation with the intensity of external light pump is attributed to the internal space charge field in the 0.3BaSrTiO3-0.7NdAlO3 ceramics caused by the excited free carriers.

In order to solve the problem that the existing terahertz (THz) characterization system does not fully characterize the sample properties, a wide-spectrum THz system based on gallium selenide (GaSe) crystals is built. Femtosecond pulse laser is used to pump the GaSe crystals, and the generated THz radiation has a broad spectral range of 10 to 20 THz. A Michelson interferometer is built to perform non-coherent characterization of the THz transient electric field. The high-frequency absorption spectra of three kinds of biological samples such as uracil are measured by the system, and the vibration and rotation of biomolecules are analyzed theoretically with density functional theory. Experimental results are in agreement with the theoretical calculations, proving that the system can quickly obtain the high-frequency information of the sample. The system makes up for the lack of information in the high-frequency band of the traditional THz spectral system and lays a solid foundation for building a high-frequency THz time-domain spectral system.

To establish a quantitative detection model of benzoic acid additive in flour, terahertz time-domain spectra of benzoic acid doped at different percentages (mass fraction) in flour are collected, and the absorption coefficient spectra are obtained through calculation. It is found that the absorption peak amplitude is positively correlated with benzoic acid content. As for the detection method, first, we explore the effects of different spectral pretreatment methods on THz spectroscopy, and then adopt methods like smoothing correction, multiple scatter correction (MSC), baseline correction, and normalization correction to perform the appropriate processing. Subsequent to correction, PLS model is established to select the optimal pretreatment method. Experimental results verify that PLS model established subsequent to normalization is more optimal, with the correlation coefficient of prediction (rp) observed to be 0.9790 and root-mean-square error of prediction (RMSEP) observed to be 1.28%. We establish PLS, least squares support vector machine (LS-SVM), and back propagation neural network (BPNN) regression models for the determination of benzoic acid content in flour. It is proved that the most optimal quantitative determination model of benzoic acid content in flour is BPNN model with correlation coefficient of prediction (rp) of 0.9945 and root-mean-square error of prediction (RMSEP) of 0.66% subsequent to the normalization of terahertz absorption coefficient. It is concluded that a new solution for the nondestructive detection of benzoic acid additives in flour has been developed, and provide guidance for the detection of other types of additives, all of which are essential for the healthy development of the flour industry.