A passive and non-contact current sensor based on giant magnetostrictive material (GMM) and fiber Bragg grating (FBG) is proposed. The position of reference GMM, the size and direction of the reserved expansion space of the magnetic concentrator, the side length of the cross section and the length of the upper opening are analyzed and optimized by COMSOL software, so as to ensure the dense and uniform distribution of magnetic force lines in the bonding area of the sensing FBG. Finally, the temperature independence of the current signal is measured by the double grating-intensity demodulation system. The alternating current (AC) and direct current (DC) characteristic test of the sensor shows that the sensitivity of the sensor is 249.75 mV/A under the DC input of 0.8--3.5 A, and the linear correlation coefficient is as high as 0.9942. Under the action of a bias current of 1.6 A, the sensor has a good response ability to the sinusoidal input signal of 50 Hz--6.5 kHz. At the same time, the test of the temperature characteristic of the sensor shows that the double grating-intensity demodulation method can eliminate the influence of ambient temperature on the output voltage to a great extent. The sensor proposed in this paper has the advantages of small size, simple structure, stable performance, and low cost, and has temperature-independent characteristics.

A generation scheme for terahertz (THz) quadrature phase shift keying (QPSK) signals over fiber based on on-off-keying (OOK) modulation is proposed. A pair of optical octave sideband signals is generated by a dual-parallel Mach-Zehnder modulator (DP-MZM), and two independent OOK baseband signals are modulated to two polarization states of the octave sideband signals by two intensity modulators (IMs). The two polarization signals are superimposed after phase and amplitude adjustment, and the superimposed optical signal undergoes photoelectric conversion at the terminal after power amplification and optical fiber transmission. THz QPSK signals are thereby generated. In the VPI simulation environment, the transmission performances of 80, 240, and 400 GHz signals are verified. The results show that the bit error rate (BER) of a QPSK signal with a baud rate of 20 GBuad and a frequency of 400 GHz generated by the proposed scheme is below the forward-error-correction threshold (3.8×10 -3) after the signal is transmitted over a 40 km zero dispersion shifted fiber (DSF). Our proposed scheme, with no need for pre-coding or a digital-to-analog converter, reduces the complexity of signal processing and system cost.

A refractive index detection sensor for four-pole suspended core fibers with a small core diameter is designed, and three different polishing structures are simulated for this fiber. The open air holes are coated with gold film to stimulate the surface plasmon resonance effect. The finite element method (FEM) is used to analyze the surface plasmon sensing characteristics of the open suspended core fiber, and the influences of the geometric parameters of the sensing metal layer and the thickness of the suspended poles on the sensing effect are studied. The single-hole polishing structure and the opposite two-hole polishing structure have a refractive index detection range of 1.31—1.42, the maximum sensitivities are 15000 nm/RIU (refractive index unit) and 16000 nm/RIU, and the resolutions are 6.7×10 -6 RIU and 6.25×10 -6 RIU, respectively. The refractive index detection range of the adjacent two-hole polishing structure is 1.31—1.40, the maximum sensitivity can reach 20000 nm/RIU, and the resolution can reach 5.0×10 -6 RIU. This sensor has good performance in measuring high refractive index substances, is easy to prepare, and has broad market application prospects in the future.

A cascaded double-cavity temperature sensor based on hollow fibers encapsulated by polydimethylsiloxane (PDMS) membrane is proposed and prepared. The sensor consists of an air cavity (FP1) and a PDMS cavity (FP2) that are cascaded, and the PDMS cavity is much shorter than the air cavity so that the sensor can meet the condition of the Vernier effect [the optical path of FP1 is close to that of the composite cavity FP3 (composed of FP1 and FP2)]. When the external temperature changes, the PDMS membrane expand to both sides, resulting in the interference spectra of FP1 and FP3 move in the opposite direction. The experimental results show that the interference spectrum of FP1 and FP3 manifest the Vernier effect, and the envelope of the interference spectrum is obvious. The temperature sensitivity reaches 1.32 nm/℃ in the range of 50--60 ℃, which is consistent with the theoretical analysis results. The proposed sensor, with the advantages of small size, light structure, high sensitivity, and simple preparation, has application potential in chemistry, biology, and medical treatment.

In order to solve the problems of capturing weak-texture features on the surface of large components and precision registration of multiple measurements, a compound measurement system integrating structured light and photometric stereo vision is adopted. The point cloud data of the overall shape of the workpiece surface are obtained by structured light measurement, and the normal vector information of the fine and weak texture of the surface is obtained by photometric stereo vision. On this basis, a new type of local feature descriptor which combines neighborhood point cloud coordinates and normal vector information is proposed, which can describe the surface features of weak-texture workpieces effectively and robustly. Extensive simulations and practical experiments verify the effectiveness of the proposed method, and its performance greatly surpasses the iterative nearest point algorithm based on traditional feature descriptors. The proposed method can effectively capture and describe the rich detail features of the weak-texture surfaces, construct robust and significant feature descriptors, and then greatly improve the matching accuracy of the measurement results and reduce the overall reconstruction error of large and complex components.

In imaging electron optics, the electrostatic focusing concentric spherical system has a series of valuable properties, its potential distribution and electron trajectory can be represented by analytical form, and the electron optical imaging characteristics and its lateral aberrations can be quantitatively studied. Although there are many literatures on electron optical imaging, they are limited to the understanding of zero-order approximation imaging, and a lot of fallacies exist in it. This series of articles fully study the electron motion trajectory, electron optical imaging characteristics, and lateral aberrations in the electrostatic focusing concentric spherical system composed of two electrodes or multiple electrodes, investigate the image dispersion formed by the electron beam in the imaging segment, put forward some new idea and recognition, correct some fallacies in literatures, and establish my own theoretical system. The first article of this series mainly explores the electron moving trajectory under the electrostatic field in the concentric spherical electrostatic focusing system composed of two electrodes, deduces the new representations for the trajectory of electrons emitted from the photocathodes of the concentric spherical system with electrostatic focus of two electrodes in the polar coordinate system ρ=f(φ) and in the cylindrical coordinate system r=r(z), and explores the exact and approximate formulae of axial intersection position and its angle of inclination at the image section for the electrons emitted from the photocathode. This paper lays a foundation in studying the electron optical properties and lateral aberrations of the electrostatic focusing concentric spherical system.

On the basis of the part A, this paper goes further study the electron optical lateral aberration of axial points of the bi-electrode electrostatic focusing concentric spherical system. It shows that the image diffusion of axial points formed by the electrons emitted from the photocathode in an electron optical system is composed of two parts: the paraxial lateral chromatic aberration and the geometric lateral spherical aberration. This confirms that in the electrostatic focusing concentric spherical system, the second order paraxial lateral chromatic aberration of the cathode lens, that is, the Recknagel-Apцимович formula, is generally valid. This paper also studies the differences of lateral aberrations of axial points between the wide electron beam and the narrow electron beam. Finally, a special case of transit of the proximity focusing system from the bi-electrode electrostatic focusing concentric spherical system is also investigated.

In view of the fixed-focus nature of imaging of the bi-electrode electrostatic focusing concentric spherical system, the image plane position and the magnification of system are immediately determined when the geometry of the system is relatively fixed; if the electrical parameters of the system are changed, the changes of the image plane position and its magnification will be extremely tiny. This paper studies the variations of the electron optical imaging characteristics and its lateral aberrations when inserting a large number of gate electrodes into the bi-electrode electrostatic focusing concentric spherical system composed of the photocathode and the anode. This paper once again confirms that for the multi-electrode electrostatic focusing concentric spherical system, the second-order paraxial lateral chromatic aberration of the imaging electronic optical system, i.e., the Recknagel-Apцимович formula, is still valid. The electron optical imaging characteristics of the tri-electrode electrostatic focusing concentric spherical system are emphatically discussed.

Start from the second-order paraxial lateral chromatic aberration of the cathode lens, that is, from the well-known Recknagel-Apцимович formula in the imaging electron optical system, this paper investigates the minimum diffusing circle formed by the electron beam, studies the determination of the position of the optimal imaging plane, investigates the contour of crossover formed by the electron beam emitted from the whole photocathode surface, as well as the diffusion circle on the cathode surface formed by the electron beam emitted from the origin, and depicts the envelope of the electron rays formed in the imaging section. The present paper will help the readers to understand the moving electron trajectory in the image tubes, as well as its beam convergence and divergence in the imaging section.

To overcome the limitation of traditional stereo-vision position and pose measurement methods that the number and locations of calculation points must be determined in advance, this paper proposes a method to measure the positions and poses of spatial objects based on three-dimensional digital image correlation (3D-DIC). In this method, full-field coordinates of the measured object at different moments are obtained by 3D-DIC. According to the coordinates of corresponding calculation points extracted, position and pose parameters of the spatial object are solved via space vectors. The number and locations of calculation points can be selected flexibly in this method, and a criterion of the optimal ratio of the number of calculation points (ORNCP) is also proposed accordingly. Multiple position and pose parameters of mask samples with complex morphological characteristics are measured on a displacement and rotation platform as well as a 6 degree-of-freedom (DOF) platform, respectively, for experimental verification. The experimental results demonstrate that position and pose measurement precision is the highest when the number of calculation points meets the ORNCP criterion. Meanwhile, the positions of calculation points have little influence on experimental results, and the measurement errors in the case of the 6 DOF platform are within the tolerance range. The proposed 3D-DIC position and pose measurement method can be used to measure multiple position and pose parameters of a spatial object within a small error range.

A self-built device for measuring the angular velocity of falling object in the process of free falling is introduced, and the influence of rotation error caused by different angular velocities of falling object on gravity measurement is evaluated. Aiming at the free-falling motion model of a falling object with an initial rotation speed in a vacuum cavity, the device adopts the principle of optical lever and uses a high-precision position sensitive detector (PSD) as a light tracking device to study and deduce the relationship between the reflected light displacement caused by rotation and the falling time. Then, the time displacement curve recorded by PSD is fitted to solve the rotation angular velocity of the single fall of the falling object. After adjusting the verticality of the vacuum cavity, the maximum rotational angular velocity value can be reduced to 16.88 mrad/s, the introduced gravity measurement uncertainty is 0.57 μGal, indicating that the falling object is released more stably at this state. The experimental results show that the device can not only further improve the installation and adjustment accuracy of the falling object transmission structure in the absolute gravimeter, but also monitor the attitude of the falling object in the working process of the optical interference absolute gravimeter, and further reduce the measurement uncertainty introduced by the falling object rotation.

During insect flight, some overlapping phenomena such as torsion, bending, and warping will appear in the wings, which makes the wings shielded from each other and thus leads to hard discrimination of the flight attitude by traditional optical measurement. To realize the dynamic measurement of mutual occlusion of transparent membranous wings, this paper proposed a three-dimensional (3D) digital image correlation method based on fluorescence polarization imaging to measure the 3D full-field deformation of multi-wing structures. According to the principle of polarization imaging, the 3D morphology of a monochromatic wing can be measured by a single polarization camera in the presence of a splitting optical path integrating mirrors, polarizers and a splitting prism. Depending on the spectral characteristics of fluorescent speckles, different fluorescent speckles were fabricated on different wings that were shielded from each other, and a band-pass filter was used to separate the fluorescent speckles of specific spectra on them, which enabled the independent imaging and synchronous measurement of multiple wings. Firstly, the measurement experiments of the relative surface topography and deformation of the sheet with equal thickness were carried out to calibrate the measurement accuracy of multiple mutually shielded surfaces. Further, the different overlapping forms of insect wings (cicadas) were measured, and the 3D profile of any mutually shielded wings was given to verify the feasibility of the measurement method.

Regarding surface emitting distributed feedback (SE-DFB) semiconductor laser as the research object, this paper investigates the controlling effects of second-order gratings on the emission characteristics of the laser characterized by the coupling coefficient in light of the coupled-mode theory. The finite-difference time-domain (FDTD) method is used to simulate the grating structure and optimize the grating parameters. The distributed Bragg reflector (DBR) is introduced onto the substrate of the laser to coordinate with the gratings to control the emission characteristics. With a 980 nm semiconductor laser, this paper focuses on the comprehensive influences of various parameters on the grating coupling coefficient to obtain the optimal grating parameters. Those parameters include DFB grating duty cycle, length of DFB grating period, etching depth of DFB gratings, tooth angle of DFB gratings, duty cycle of the DBR reflector, material refractive index of the DBR reflector, and number of period medium layers of the DBR reflector. This research provides a theoretical basis for the design and fabrication of subsequent devices.

Thin disk lasers are becoming increasingly popular owing to their high peak power and pulse energy. Although high-power beams can be output by such lasers, the disk crystal is liable to deformation due to thermal effects, and the result is degraded beam quality. In this paper, a simple deformable mirror is designed and fabricated to compensate for the changes in the focal power of the thin disk crystal. The curvature radius of the deformable mirror can be changed between 2.050 m and +∞ by adjusting the pneumatic pressure in the air chamber. With the deformable mirror, the operating point of the thin disk laser can shift synchronously with the change in the focal power. The radius of the laser spot on the thin disk remains the same in the whole pump range. Consequently, the thin disk laser can operate in the fundamental mode, with the beam quality factor M2 remaining no more than 1.2 under both the threshold and the maximum laser output conditions.

The laser diode (LD) is used to pump the passively Q-switched dual-wavelength laser with Yb∶YAG slab crystal, and the experimental study of controllable laser output polarization is carried out. A compact V-shaped resonator is built in the experiment, and the laser output can be switched from 0° horizontal polarization to 90° vertical polarization by adjusting the inclination of the output mirror (OC). Through the experimental design, it can be concluded that the final output polarization depends on the additional phase difference in the cavity. When the additional phase difference in the cavity is π, the output polarization changes from horizontal polarization to vertical polarization. The experimental results show that when the change of OC inclination angle is about 3.6 mrad, the linear polarization is switched from horizontal polarization to vertical polarization, the optimal extinction ratio of horizontal and vertical polarization is 28.98 dB and 25.96 dB, respectively. When the pump power is 18.42 W, a balanced dual-wavelength laser output of 1.66 W and the corresponding pulse width of 42.6 ns are obtained.

The lining is an important part of connecting the solid rocket motor shell and the propellant, and its bonding state determines the integrity of the propellant-liner-shell bonding interface, which further affects the safety and reliability of the solid motor. According to the mixed state and discontinuous impedance characteristics of the lining bonding structure, the propagation law of laser ultrasound in the lining structure is studied, and the experimental device is set up. By means of ultrasonic wave excited by ablation mechanism, the propagation time and relative sound attenuation of ultrasonic wave in the lining are extracted, and the ultrasonic transmission method is used to characterize the curing process of the lining. A calibration time difference method for solving the longitudinal wave transit time in the lining is proposed, and the relative sound attenuation model of discontinuous impedance is established. The experimental results show that the transit time obtained by the calibration time difference method and the sound attenuation calculated by the relative sound attenuation model can well characterize the curing process of the lining.

With the popularization of visual measurement technology in engineering, more and more visual calibration and measurement need to be carried out by non-professionals in the workshop site, which will cause checkerboard images to contain more noise. In order to achieve robust and accurate sub-pixel refinement of checkerboard corner under noise, a checkerboard corners sub-pixel refinement method based on edge direction projection is proposed. First, the initial edge direction is calculated based on the non-maximum suppression algorithm. Then, the edge direction is refined based on the least weighted square fitting method. Finally, the sub-pixel coordinates of the checkerboard corners are refined based on the maximum projection of the edge direction. The results show that in the high-quality checkerboard images, the maximum measurement errors of checkerboard edge length are all less than 0.021 mm, and the average measurement errors of checkerboard edge length are all less than 0.006 mm. In the checkerboard image with Gaussian noise and corner pollution, the maximum deviation of checkerboard edge length measurement of the proposed method is less than 0.05 mm, and the average deviation of checkerboard edge length measurement is less than 0.02 mm.

A new binocular camera calibration method based on a directional target and multi-constraint optimization is proposed. The novel directional planar target is equipped for determining the target rotation direction and assigning a code number to each calibration corner to ensure the matching of homonymous corners even in the case that the target is partially occluded and thereby achieve binocular camera calibration. After building a model of binocular camera calibration with a directional target, we introduce zenith and azimuth angles to describe the orientation of the planar target and select images in which the target has markedly different orientations at different positions as calibration images, so as to raise the stability of the binocular calibration results. To improve the accuracy of the binocular calibration results, we make full use of the 3D geometric information on the target and propose a multi-dimensional constraint optimization model for binocular parameters. The experimental results show that our method can effectively improve the stability and accuracy of the calibration results compared with Zhang’s calibration method. Multiple measurements of standard gauge blocks further verify the effectiveness of the proposed method.

In a graphene-based refractive index sensing system, the large range and high measurement sensitivity cannot be achieved simultaneously, and only the relative refractive index can be measured. In this study, a large-range absolute refractive index measurement method based on total internal reflection is proposed, which realizes the accurate regulation of a wide range of angles only through one-dimensional linear motion. The optical 4f system ensures that the position of the sampling point does not change with the incident angle. By the scanning measurement method at different incident angles, the measurement range of the refractive index can reach 1--1.5168 in theory. Through the refractive index measurement of calcium chloride solution with different mass fraction, the measurement sensitivity obtained in experiments is 7.203×10 -4 RIU.

The diffuse reflectance spectrum of skin contains rich tissue information, which has been widely used in the detection of physiological parameters. However, due to the complex changes of human physiological parameters and difficulties in optical data collection under various conditions, its development and application in the detection of non-invasive peripheral blood physiological parameters are limited. In view of this, Monte Carlo simulation method is used to simulate the effects of different concentrations of total hemoglobin, oxygenated hemoglobin, deoxyhemoglobin, methemoglobin and other peripheral blood components on skin diffuse reflectance spectrum and skin color, and a chromatographic fusion based analysis method for cyanosis is proposed. The results show that the skin color features can distinguish healthy, jaundice and cyanosis, and the analytical method solves the difficulty of accurately distinguishing the cause of cyanosis by skin color alone.

The ways to obtain new types of axicons and Bessel beams more effectively and easily have always been the focus of researchers. This paper proposes an axicon made of liquid crystal material with cone angle adjusted by voltage and introduces the characteristics of the proposed liquid crystal axicon. This type of liquid crystal axicon is controlled by two voltages, one of which is fixed, and the cone angle of the axicon is altered by changing the other voltage. The characteristics of the liquid crystal axicon are tested. The experimental results show that the liquid crystal axicon can modulate the incident light similar to the traditional axicon and realize the continuous change of the cone angle. Finally, an imaging system using a liquid crystal axicon is built, and the extended depth-of-field imaging is achieved by this system. The liquid crystal axicon provides new ideas and methods for generating Bessel beams and extending the depth of field.

A temperature-voltage bi-controllable broadband polarization conversion/absorption metasurface based on vanadium dioxide (VO2) and graphene is proposed. The control of the polarization conversion and absorption function can be realized by regulating the conductance properties of VO2 and graphene in the metasurface. The results show that when VO2 is in metal state and graphene is in insulating state, the metasurface operates in the broadband polarization conversion mode, achieving linear polarization conversion in the range of 1.57--2.49 THz. When VO2 is in insulating state and graphene is in metal state, the operation mode of the metasurface is switched to the absorption mode, and the absorptivity reaches 90% in the range of 1.56--2.99 THz. The polarization conversion and absorption performance can be controlled by regulating the temperature of VO2 and the bias voltage of graphene, respectively. Furthermore, the working principle of the metasurface is explained by eigenmodes, impedance matching theory, and current and magnetic field distributions. The stability of its performance under different structural parameters and incident angles is also discussed.

A double-layer metal film grating with a composite periodic structure is designed, which features multiple frequency bands, multi-characteristic integration. The simulation by a finite element method, and we find that this structure can achieve high absorption at resonant wavelengths of 760, 904, 1028, and 1216 nm under transverse-magnetic (TM) polarized illumination on the bottom of the nanograting at an incident angle of 65°. Its absorptivity can be up to 98.73%, 92.84%, 97.57%, and 99.11%, respectively. Further simulation reveals that multiband absorption peaks also possess the characteristics of narrowband polarization filtering and refractive index sensing. Its maximum refractive index sensitivity is 2080 nm/RIU and the maximum figure of merit (FOM) is 92.1 RIU -1. In addition, period modulation enables the tunability of narrowband polarization filtering in a wide near-infrared wavelength range from 944 nm to 1206 nm. We explore the underlying integration mechanism by analyzing the distributions of the surface electromagnetic field, surface current, and surface electric charges. The results show that the designed double-layer metal film grating with a composite periodic structure has a broad application perspective in miniaturized and highly integrated multispectral infrared detection, spectral imaging, and biosensing.

OJIP fluorescence kinetics is widely used in the study of algae photosynthesis, but in common OJIP curve analysis, the characteristic time of J and I points is often fixed. Therefore, the influence of algae species on the characteristic time of J and I points is ignored, which results in the deviation of the fluorescence intensity calculation results of J and I points and directly affects the accuracy of the measurement results. In view of this, a method of using three-level exponential function to approximate OJIP curve is proposed to dynamically obtain the characteristic time of J and I points. The test results of experiments of characteristic time of J and I points of different algae species, and the characteristic time of J point under dichlorophenyl dimethylurea (DCMU) stress show that the proposed method can effectively obtain the characteristic time of J and I points of different algae. The characteristic time of J point of Scenedesmus dimorpha, Chlorella pyrenoidosa, Chlorella vulgaris and Cylindrotheca closterium is 2.22, 1.52, 1.33, 1.01 ms, respectively. The corresponding characteristic time of I point is 28.80, 27.15, 29.90, 15.28 ms, respectively. The relative standard deviation of multiple calculation results is less than 10%, which has a great consistency. Under the toxic stress test conditions with DCMU concentrations (mass concentrations) of 10, 20, 40 μg/L, the characteristic time of J point of Chlorella vulgaris calculated by the proposed method is 1.25, 1.18, and 1.10 ms, respectively, and the relative standard deviation is 12.03%. In addition, the photosynthetic activity parameter VJ calculated by the proposed method has a good toxic dose-effect relationship with the DCMU concentration, and the correlation coefficient R2 is 0.991.

Spectral detection technology plays important roles in intelligent identification of next-generation smart equipment, such as visual inspection, physico-chemical analysis, and process control, which can be widely used in the fields of food safety, medical diagnosis, environmental monitoring, anti-counterfeiting identification, plant disease suppression, and military reconnaissance and early warning. Traditional spectral detection systems are limited by dispersion elements, which suffer from large volume, high cost, and poor customization capability. Fabry-Perot (FP) filtering chips based on micro-electro-mechanical system (MEMS) technology provide a new solution for the miniaturized, low-cost, and customizable spectral detection systems. In recent three decades, considerable progresses have been achieved in the area of practical MEMS-FP filtering chips, which have been widely applied to miniaturized spectral detection systems. However, many problems need to be solved in the aspects of chip manufacturing, performance improvement, and system integration. In this paper, the principle and performance, device classification, and application progresses of MEMS-FP filtering chips are reviewed. And also, the existing problems and development trends in the future are discussed.

The fourth generation synchrotron radiation light source provides X-rays with higher brightness and coherence,and better performance for many research fields. To access the full potential of these beams, accurate beamline alignment and high-quality X-ray optics are required. Wavefront metrology plays an important role in these aspects. X-ray near-field speckle based wavefront metrology, which has been developed rapidly in the past 10 years, has the advantages of simplicity and high measurement accuracy. Based on the property of not changing in shape and size of the speckle in the deep Fresnel region, the cross-correlation between the reference image and the sample image is calculated, and the wavefront information of the incident wave, the transmitted wave or the reflected wave of the optics to be measured is extracted. The present research status of X-ray near-field speckle based wavefront metrology is summarized. The principles, experimental procedures, advantages and applications of X-ray speckle tracking, X-ray speckle vector tracking, X-ray speckle scanning, self-correlation X-ray speckle scanning, unified modulated pattern analysis and Ptychographic X-ray speckle tracking are introduced.

In view of the fact that the spectrum recovered by the nonlinear optical path difference will appear additional frequency noise, which will lead to the broadening of the restored spectral line and seriously affect the spectral quality, a method for interferogram nonlinear optical path difference correction and wavelength calibration is proposed by measuring the characteristic light source only once. By single measurement of the characteristic light source, the interferogram can be obtained, the nonlinear phase and approximate central frequency contained in the interferogram can be calculated, and the relative optical path difference can be calculated. Then, the nonlinear mapping relationship between the optical path difference and the sampling point can be obtained. Finally, the nonlinear optical path difference can be corrected by the secondary sampling. Taking the static birefringence Fourier transform spectrometer as an example, the nonlinear optical path difference model of the system is constructed, and the correction method and principle of nonlinear optical path difference are given. Then, the mercury argon lamp is used as the characteristic light source, the characteristic spectral lines of mercury argon lamp are extracted by the obtained interferogram, and the influence of different wavelengths on the nonlinear optical path difference is analyzed. Finally, the nonlinear optical path difference is corrected and wavelength is calibrated. The experimental results show that the half-peak full width of the spectral line at 546.074 nm changes from uncorrected 9.08 nm to 4.14 nm, indicating that the proposed method effectively improves the resolution and accuracy of the spectrometer.

The preparation of high-quality gallium oxide (Ga2O3) films is one of the premises for the realization of high-performance Ga2O3 electronic and optoelectronic devices. In this study, Ga2O3 thin films are deposited on a sapphire substrate by pulsed laser deposition (PLD) technique at room temperature and annealed in an oxygen atmosphere. In this way, we can study the change rules of the properties of Ga2O3 thin films. The results show that the Ga2O3 thin films deposited at room temperature are amorphous. With the increase in annealing temperature, the crystallization degree of the thin films and the optical band gap increase. Both Ga 3+ and Ga + oxidation states are detected in Ga2O3 thin films before and after the annealing, which indicates the Ga2O3 thin films are deficient in lattice oxygen. When the annealing temperature increases, the percentage of lattice oxygen increases, the percentage of low valence state Ga +decreases, and the quality of thin films is enhanced. However, a high annealing temperature will lead to the diffusion of aluminum in the substrate into the thin film, and thus the quality of the thin film deteriorates. In addition, the thermal expansion coefficient and lattice mismatching between the poor-quality thin film grown at room temperature and the substrate cause the crack of the Ga2O3 thin film after high-temperature annealing.

Airy pulse, especially chirped Airy pulse, has attracted more and more attention and research because of its unique properties. However, due to the complexity of chirped Airy pulses, there are few experimental reports about chirped Airy pulses. In view of this, the chirped Airy pulse can be obtained by modulating the chirped Gaussian pulse in theory, and the modulation mechanism and the transmission properties of the modulated pulse are studied. The results show that the like chirped Airy pulse obtained after modulation is basically the same as the chirped Airy pulse, and has the transmission property of the chirped Airy pulse, which proves the feasibility of the chirped Airy pulse obtained by modulating the chirped Gaussian pulse.