Based on the extended scalar diffraction theory, the relative diffraction efficiency of any diffraction order is deduced considering the azimuth of incident light (conical diffraction) for transmission and reflection. It is proved that the relative diffraction efficiency formulas are different when using the extended scalar theory for a blazed grating bounded by the plane and medium interface, respectively. However, the optimized depth and blaze wavelength are the same, with corresponding explicit expressions provided. The two relative diffraction efficiency formulas are applied to a blazed grating with specific parameters to compare with rigorous coupled-wave analysis. The results show that the difference between the two formulas is minimal, and both are consistent with the rigorous coupled-wave analysis.

This study theoretically analyzed the reasons why, in the copolarized dual-pump scheme, wavelength conversion does not change the probability distribution of the probability shaping (PS) signal and the order of orthogonal frequency division multiplexing (OFDM) signal subcarriers can remain unchanged. Then, after all-optical wavelength conversion, the transmission of the PS-64QAM-OFDM signal through a highly nonlinear optical fiber in a homodyne coherent detection system was experimentally verified. Finally, the experimental results indicate that when the baud rate is 20 Gbaud and the bit error rate is 1×10-2, the optical signal-to-noise ratio (OSNR) loss of an ordinary 64QAM signal is 1 dB, and the OSNR loss for PS-64QAM signal is improved by 0.5 dB.

Phase sensitive optical time domain reflectometers (φ-OTDRs) have been widely employed in pipeline safety early warning systems, optical cable break-point searches, mechanical pipeline pig (PIG) positing and tracking, and other fields. The sensing optical cables of φ-OTDRs are mostly buried underground so that the soil characteristics, transmission distances, and optical cable structures all have considerable effects on the signal characteristics. This study considered the propagation characteristics of vibration signals in soils and explored the effects of non-event factors such as optical cable structures, soil moisture, and transmission distances on the signal characteristics of systems. In addition, in terms of energy change trends in characteristic frequency bands, the difference between real shock vibration and non-event signal fluctuations was investigated. A proposed method to judge external shock vibration is derived from the results.

With the rapid development of the Internet of Things, smart devices require high-precision, real-time location services. However, only two-dimensional positioning can be achieved in existing visible light positioning technologies; furthermore, the system is complex and has a low positioning accuracy and extended positioning time. To address these issues, this study proposes a visible light three-dimensional positioning system based on two light-emitting diodes (LEDs) and image sensors. First, a simulation model is established by combining the pinhole imaging model and the distortion model. Next, a stripe search algorithm based on bisection and a double pointer is proposed to rapidly determine the position of the LED on the image. Finally, the geometric features of the LEDs on the image are used to achieve three-dimensional positioning. After calculations, in a 100 cm×100 cm×300 cm space, the average positioning error of the simulation experiment is 0.79 cm, and the average positioning error of the physical experiment is 5.61 cm. The average positioning time is 64.13 ms. In addition, the time performance of the proposed stripe search algorithm is improved by 70.06% compared with that of the linear stripe search algorithm. Therefore, the proposed system can provide a good three-dimensional positioning service.

The zoom principle and primary aberration theory are used to study the design method of a mechanically compensated all-off-axis reflective three-gear zoom optical system with long focal length. The initial structure solving model for coaxial four-reflective mirrors zoom optical system is developed and based on the model, the adaptive variant probability genetic algorithm developed is used to address it and the partial initial structure parameters of the coaxial system is obtained; further, it is properly made off-center and tilt to remove the central obscuration issue of the coaxial optical system, and the aberration of the off-axial system is corrected using optical design software Zemax. Using the design method discussed above, an aspheric surface design is adopt in the optical surfaces of the system’s all-reflective mirrors, yielding a high imaging quality off-axis four-reflective mirrors zoom optical system with three-gear zoom focal lengths of 300 mm, 600 mm, and 900 mm. The results show that the method provides an effective measure for an off-axis all-reflective three-gear zoom optical system and that the system can be designed to meet practical needs.

Lommel beams are a type of complex-structure nondiffractive beams expressed by the Lommel function. Their optical features can be adjusted using three parameters: order n, asymmetry c0, and rotation angle ?0. However, the optical structure of a Lommel beam is complex, making it challenging to be produced experimentally. In this study, we introduce a complex amplitude modulation technique to generate nondiffractive Lommel beams. The amplitude and phase of complex wavefronts are simultaneously encoded using the Lohmann-type detour phase-coding method. High-quality Lommel beams are produced by processing the computer-generated hologram into a real amplitude mask using the holographic direct-writing printing system. In the experiments, the mask plate reaches 35000 pixel×35000 pixel. Furthermore, this study provides a general approach for producing nondiffractive beams with other different complex structures.

A general relationship of three-dimensional-two-dimensional (3D-2D) object image mapping of line vector is proposed to solve the common adaptation problem of optical pose processing of typical rigid targets (mostly with linear externalization characteristics) in the shooting range. The pose information is then obtained by choosing a line vector for object image direction mapping and matching. First, the linear vector of the target body is rotated, the theoretical correspondence between the line vector of the key subject and the calculated pose angle is obtained, and then the key vector is projected to the determined image plane, the mapping relationship between the spatial line vector and the image of the projected image plane is established for the first time, and the spatial line vector is reconstructed using the substation mapping results, in order to achieve the purpose of closed-loop verification of the correctness of the mapping results. The pure direction pose is solved using the significant line vector 3D-2D pose mapping relationship presented in this paper for optical pose processing based on line vector. Especially in the process of occlusion and transformation in the medium and long-term dynamic target attitude measurement, it has good adaptability. Compared with the existing pose processing results, the correctness and reliability of the algorithm are verified.

Simulation preassembly based on line feature matching is a preassembly method used for bridge steel components. In this method, components are spliced based on line feature matching of the joint. However, under this method, the overlap rate is not high and the linear accuracy is not considered. Therefore, an improved method aided by design data is proposed herein. First, the reduced bounding box and slicing methods are used to extract the line features of the joint of the components and linear features, respectively. Next, the line features, combined with those extracted from the design data, are fused into the target and source features according to their corresponding relationships. Then, coarse and fine registrations are completed based on point feature histograms and iterative closest point, respectively.Finally, component splicing is conducted using the registration results. The accuracies of the three methods of corner and line feature matching, and the method aided by design data are compared based on simulation data. Results reveal that the method aided by design data can effectively improve linear accuracy. In an actual field experiment, the processing quality of the steel components of the Shanghai Nanheng River Bridge is inspected by line feature matching and the method aided by design data, respectively. The inspection results indicate that the proposed method is practical and can effectively improve the linear accuracy.

In order to make the spatial amplitude modulation polarization spectrometer have the minimum sensitivity to the system error, we take the condition number of the measurement matrix as the objective function, and use the genetic algorithm to simulate and analyze the optimal combination of the double composite optical wedge crystal axis azimuth and the polarizer azimuth in the modulation module of the instrument, and give the corresponding optimal angle combination. With the measurement accuracy of the degree of polarization as the evaluation function, the simulation experiment is carried out for a variety of different angle combinations within the given device error range. Simulation results show that According to the simulation results, when the measurement matrix condition number of the instrument angle parameter combination is 1.733, there is a 98% chance that the polarization degree measurement accuracy will be better than 0.01, this probability is 23% and 64% higher than the probability for the angle parameter combination with the measurement matrix condition number of 1.966 and 3.257, respectively. This study provides a theoretical basis for the design and selection of the parameters of the spatial amplitude modulation polarization spectrometer components.

Laser-induced forward transfer has application prospects in three-dimensional metal microstructure printing. Pulse duration is a critical factor that influences the droplet transfer behavior, but droplet generation and deposition behavior under different pulse durations are unclear at present. In this study, 500 nm copper films were used as the research object to perform a laser-induced forward transfer experiment at five pulse durations. The results show that with an increase in pulse duration, the minimum and maximum energy fluence thresholds of the laser-induced forward transfer process to form complete microdroplets gradually increase, and the pulse duration significantly influences the morphology of deposited microdroplets. Based on the experiment, the processing map of laser-induced forward transfer under different pulse durations was plotted, and the material transfer rates of microdroplet deposition at different pulse durations were calculated. Finally, the large-area microdroplets array was printed using the scan head line-scanning method.

Laser cladding technology was used to prepare TiC particle-reinforced Fe-based composite coatings on 304 stainless steel to improve its surface properties. The effects and reasons of laser power on the geometrical microstructure characteristics and hardness of the cladding layer were investigated. The microstructure characteristics of the cladding layer were comprehensively characterized by grey relational analysis. The height, porosity, and content of unmelted TiC particles reduced as laser power rose, whereas the width, depth, dilution rate, and secondary dendrite arm spacing of precipitated TiC increased. The amount of precipitated TiC increased and then decreased, whereas the secondary dendrite arm spacing of the matrix decreased and then increased, reaching their maximum and lowest points at 1800 W, respectively. The surface of the cladding layer is well-formed when the laser power reaches 1800 W. It has a well-balanced microstructure and the grey relational grade is maximum. The cladding layer has an average hardness of 801.5 HV0.5, which is roughly 4.5 times that of the substrate. In addition, the dissolving mechanisms of TiC particles during the laser cladding process were deduced. There are two dissolving mechanisms for TiC particles, which are distinguished by outward-inward and integral decomposition. Both processes work together to cause TiC particles to dissolve completely.

TiC-reinforced Fe-based composites are prepared to improve the surface mechanical properties of 65Mn steel and explore the effect of TiC content on the cladding morphology and forming quality of Fe-based coatings. The TiC/Fe-based ceramic composite coating was fabricated on the surface of 65Mn steel by laser cladding technology. The effects of different TiC contents on the quality (porosity), aspect ratio, and microhardness of the cladding layer are compared. The results show that with increasing TiC content, the aspect ratio first increases and then decreases. When the mass fraction of TiC is 30%, the aspect ratio reaches a maximum of 5.31, and the porosity decreases. The addition of an appropriate amount of TiC can effectively improve the hardness of the composite coatings, but very high TiC content results in excessive gas in the molten pool. Thus, the porosity increases and good coating performance cannot be obtained. The results of this study are expected to play a guiding role in the field of agricultural machinery tools.

In order to improve the surface quality of single-point diamond cutting single-crystal germanium, the orthogonal experiment of three factors and four levels is carried out, and the effect of cutting parameters on the surface roughness under the condition of uneven surface quality distribution of single-crystal germanium is studied by variance analysis and range analysis. The test results show that the contribution rate is the highest when the spindle speed has obvious influence on the surface roughness value, indicating that the larger the spindle speed is, the smaller the surface roughness value is. As a result, an optimal combination of the cutting parameters obtained is that a spindle speed of 3800 r/min, feed rate of 2 mm/min, and maximum cutting depth of 5 μm. Under this cutting condition, high-precision single-crystal germanium with a surface roughness of 2.4 nm is obtained. Next, the surface quality is good and the surface is relatively smooth according to the scanning electron microscope. The chips during cutting are banded, and the material is removed in the plastic range.

In this study, ultrafast third-order optical nonlinearity of ZnO crystals with different crystal planes and doping under femtosecond linearly/radially polarized light (330 fs, 532 nm) excitation is investigated. First, the band gap of ZnO crystals is analyzed using an ultraviolet-visible spectroscopy absorption spectrum. Next, the third-order optical nonlinearity of the ZnO crystals under femtosecond linearly/radially polarized light is measured using the Z-scan technique. The results show that the nonlinear saturation absorption effect and self-focusing effect are observed in ZnO crystals with different crystal planes and doping under the excitation of linearly and radially polarized lights owing to the electron transition in the defect state of the ZnO crystals. The third-order optical nonlinearity of ZnO[101] is the strongest for femtosecond linearly polarized light excitation, owing to the third-order optical nonlinearity of near-resonance enhancement caused by the narrowed energy bandgap in ZnO crystals. However, under the excitation of radially polarized light, ZnO[110] has the strongest third-order optical nonlinearity, probably owing to the combination of the narrow energy bandgap and the anisotropic nonlinearity caused by the axisymmetric polarization of the femtosecond vector laser. This study has potential application value in saturable absorbers, ultrafast light field regulation, and super-resolution imaging.

A uniform lighting design method based on a double free-curved surface is proposed herein. According to the theory of geometrical optics and energy mapping relationship, a double free-form surface lens is designed with a distance-to-height ratio of one. By discretizing the extended light source and lens surface, a new double free-form surface lens profile is constructed by inverse tracing the extended light source. The optical properties are simulated by using optical simulation software. The results have shown that uniform circular illumination distribution with a radius of 1000 mm is achieved on the target surface 1000 mm away from the extended light source, and the illumination uniformity is 92.3%. This method can effectively improve the illumination uniformity of the target surface based on an extended light source, and the design process of the free-form surface does not depend on feedback optimization. Accordingly, the design time is reduced and the process becomes simple and convenient.

We present a large range pressure sensor based on asymmetric Mach-Zehnder interference (AMZI) and a three-dimensional (3D) printed stereolithography resin module. The filtering characteristic is analyzed, and formulas show that the sensor's sensitivity is proportional to the length of one arm and inversely proportional to the diffraction order. In our design, high sensitivity is realized by a small diffraction order. The AMZI pressure sensor is fabricated using planar lightwave technology, and the pressure block is 3D printed with resin (DM11). The measured sensitivity is 0.3047 nm/MPa.

A liquid crystal lens is a type of optical lens that can be electronically focused without mechanical movement. This paper proposes a large-aperture liquid crystal lens that is divided into multiple Fresnel zones. To guarantee the optical power and response speed, the aperture of the liquid crystal lens is significantly improved to 1 cm. The Fresnel zones are connected and controlled by means of interdigital electrodes, and the driving voltage of each Fresnel zone is the same, which simplifies the driving method. The optical power of the newly proposed Fresnel liquid crystal lens can be controlled between -1.62D and +1.57D via the applied voltage. After the incident plane wave is modulated by the Fresnel liquid crystal lens, the wavefront is close to a parabolic distribution. This lens shows favorable optical characteristics. In this work, the lens is used as a focusing element in an imaging system for demonstration purposes.

Spontaneous Raman spectroscopy exhibits a broad spectrum and high resolution but weak signals; thus, the influence of stray light cannot be ignored. In this study, the mechanism of stray light generation in a self-designed single-cell Raman spectrometer system under gyration rotation is investigated. Moreover, the stray light suppression method is established, particularly the design method for eliminating a stray light optical trap in a multi-structure. The effectiveness of stray light suppression is verified using TracePro software simulation. The analysis results show that after stray light suppression the stray radiation ratios at different wavelengths decrease by 12%?47%, and the overall stray light level of the cell Raman spectrometer is lower than 10-6. The spectrometer, after the stray light suppression, is valuable for detecting weak light signals.

Recently, Rh nanostructures have attracted significant research attention because of their strong localized surface plasmon resonance (LSPR) at ultraviolet wavelengths and stable physical and chemical properties. In this study, the extinction properties and electric field intensity distribution of cylindrical Rh nanostructures in 200?400 nm wavebands are systematically simulated and analyzed using the finite-difference time-domain method to examine the LSPR of Rh nanostructures. The results show that the LSPR properties of Rh nanostructures are significantly correlated with the diameter, height, spacing, and peripheral refractive index. The LSPR resonance wavebands of Rh nanostructures can be effectively modulated by varying the structural parameters. This study provides a reference for applying the LSPR of Rh nanostructures in areas such as ultraviolet absorption and optical detectors.

Conversion gain is an important parameter of low-light CMOS image sensors, and realizing improvements in conversion gain helps to enhance their signal-to-noise ratio, which in turn improves their sensitivity and imaging quality. Because the conversion gain is inversely related to the parasitic capacitance of a pixel, this paper proposes a two-dimensional physical model of the parasitic capacitance of a 4-transistor active pixel based on the self-alignment technique to effectively improve the conversion gain. The proposed model establishes the relationship between pixel parasitic capacitance and injection conditions, which include injection dose, injection energy, and reset voltage. The calculated results of the model are in good agreement with the TCAD simulation results, and the variance between them is less than 0.0028 fF2, verifying its accuracy. The proposed model can be applied to the design and optimization of high-performance image sensors, especially high-sensitivity low-light image sensors.

The Einstein probe is a mission for time-domain astronomy. The follow-up X-ray telescope is a scientific payload on the EP. FXT is equipped with a nested gold-plated nickel Wolter-I X-ray telescope, which has an advantage in terms of angular resolution, a critical performance parameter for the Wolter-I X-ray telescope. The Wolter-I X-ray focusing mirror contributes the most angular resolution of the telescope. The angular resolution is typically represented in terms of the half-power diameter. Because its optical path is the same as X-rays, visible light can be used to measure the angular resolution performance of focusing mirrors instead of X-rays. However, this also results in the effect of visible light diffraction. This work evaluates the diffraction effects in a visible light test and derives an equation for determining the diffraction distribution of an annular aperture with a very high obstruction ratio based on the Fraunhofer diffraction theory. The angular resolution is measured as 32.02"±0.44" in the visible light test using the 18th EP-FXT mirror shell under a 473 nm parallel laser, and the contribution of the visible light diffraction is calculated to be 20.15". The value for the mirror shell is 24.90"±1.61". Compared to the 100 m vacuum X-ray calibration facility measurements of 25.10"±1.55" at the Institute of High Energy Physics, Chinese Academy of Science, these results are consistent within the margin of error.

In a coupled-cavity system consisting of a single-cavity optomechanical system and an auxiliary cavity, we theoretically investigate the characteristics of optomechanically induced amplification and the slow light effect. The results show that if we adopt a high-quality auxiliary cavity (with a small decay rate), the strength of the probe field in the system can be strongly amplified. Based on the perfect optomechanically induced transparency, we also find that the time delay in this model can easily surpass its upper bound in the single-cavity optomechanical system. Additionally, the system is used to study the interesting phenomenon of perfect optomechanically induced absorption. We believe that the results can be used to control optical transmission in modern optical networks.

This paper proposes a phase encoding, continuous-variable quantum key distribution quantum-state identification method based on the K-nearest neighbor algorithm. The algorithm achieves recognition using the phase features of the accepted quantum states, which are first learned from a training set consisting of known coherent states and then classified according to the phase features extracted from the unknown quantum states. Moreover, this paper derives the secure code rate of the K-nearest neighbor-based identification method under collective attack and reverse coordination and compares the performance of the method applied to four-state and eight-state protocols under different transmission distances, modulation variance, and excess noise. The results of numerical simulation results show that the method can effectively generate secure keys with a transmission distance of 250 km when the secure code rate is 10-5 bit per symbol.

In this study, an all-dielectric metasurface refractive-index sensor consisting of an array of cylindrical nanoholes is proposed. In-plane symmetry breaking of the structural unit is introduced by translating the nanoholes, and asymmetric dielectric nanohole arrays can achieve quasi-bound states in the continuum (BIC) resonance mode with a high-quality factor (Q-factor) by electric quadrupole (EQ). The relationship between the structural asymmetry parameters and the radiative Q-factor of the Fano resonance is theoretically analyzed. It is found that the mode is a symmetry-protected BIC, and near-field analysis and multipole decomposition show that the EQ plays a dominant role in the resonance mode. In addition, the influence of structural parameters on Fano resonance is analyzed, and the spectral response of the refractive index of the medium is calculated. The sensitivity of the structure reaches up to 512 nm/RIU (refractive index unit), the Q-value is 2568.7, and the figure of merit (FOM) is 760. The proposed structure has potential applications in highly sensitive biosensors in the near-infrared range.

This study designs and fabricates a dual-parameter measurement sensor based on a multi-mode thin-core multi-mode fiber structure. Mach-Zehnder interference (MZI) and surface plasmon resonance (SPR) are simultaneously generated in this structure to measure the refractive index and temperature. Two multi-mode fibers (MMFs) are used as the input and output couplers, and the thin-core fiber (TCF) is coated with a metallic silver film as the sensing arm. The refractive index sensitivity of MZI and SPR is -70.373 nm/RIU and 4888.77 nm/RIU in the range of 1.333?1.412 RIU, and the temperature sensitivity is 73.48 pm/℃ and -0.3215 nm/℃ in the range of 20?80 ℃, respectively. The sensitivity matrix is used to realize the two-parameter measurement, resolving the cross-sensitivity of the temperature of the refractive index sensor. The sensor is characterized by low cost, high sensitivity, and simple fabrication. Moreover, it has good application prospects in biochemical medical detection.

The power improvement of semiconductor lasers is of great significance to several fields, including those of national security, laser communication, laser detection/sensing, laser lighting, medical treatment. As the semiconductor laser beam combining technology can considerably improve the output power while ensuring the beam quality, it has attracted wide attention in recent years. Spectral beam combining (SBC) and coherent beam combining (CBC) are two typical semiconductor beam combining technologies, and many institutions have made breakthroughs in relevant research. In this paper, the development of these semiconductor laser beam combining technologies is reviewed and their prospect is discussed.

The quality of laser cladding coating is determined by various process parameters and their interactions. Shape control of cladding coating can be realized by optimizing process parameters. In this paper, from the perspective of traditional optimization methods and intelligent optimization methods, the research status of cladding coating quality optimization at home and abroad was described in detail, the advantages and disadvantages of various optimization methods were summarized and discussed, and the role of different optimization methods in improving coating performance was analyzed. Finally, the future development trend of coating quality optimization method was prospected. The purpose of this paper is to provide an optimization method for the preparation of high quality cladding coating and to provide a reference for the future research of laser cladding process optimization method.

The random metal grid transparent conductive film is a metal grid transparent conductive film with irregular structure, which has good light transmission and electrical conductivity. Compared with the regular structure metal grid transparent conductive film, the random metal grid transparent conductive film has better optical diffraction performance under the premise of the same optoelectronic performance. In addition, the random grid transparent conductive film based on the crack template method has obvious cost-effective advantages compared with the traditional metal grid transparent conductive film, so it has attracted much attention. The performance, research status, related preparation technology, and the latest research progress of random metal grid transparent conductive films with three structures of artificial random network, bionic random network, and self-splitting random network are discussed in detail. On this basis, the related applications of random grid transparent conductive films are introduced. Finally, the future research priority and development direction of random grid transparent conductive films are prospected.

Phase-shifting interferometry is a noncontact optical measurement method with high sensitivity. This method is widely used in optical surface and deformation measurements. However, environmental vibrations can have a significant influence on the obtained measurement results, producing fringe jitter and interference pattern ambiguity. To address these issues and improve the stability of phase-shifting interferometry, the anti-vibration technique can be used. In this article, the anti-vibration technology is divided into active and passive categories. Active anti-vibration is used for vibration isolation, that is, weakening the intensity of the vibration signal transmitted to the interference system. Passive anti-vibration is used to eliminate the influence of vibration on interferometry. Several types of passive anti-vibration technologies have been developed so far. In this article, existing passive phase-shifting interference anti-vibration technologies are classified and compared with respect to the frame number and real-time performance. Furthermore, the development direction of phase-shifting interference measurement anti-vibration technology is discussed.

Excimer laser is a kind of deep-ultraviolet laser source with high power output, which has unique applications in many aspects. However, there is still a gap between the domestic excimer laser industry and foreign countries in key technologies and high-end products, and there is a situation of stuck neck. First, this paper introduces the basic characteristics, application classification, briefly development and status of excimer laser. Second, the basic structure and some key technologies of practical devices of discharge-pumped excimer laser are introduced, including fast pulse excitation source, gas discharge cavity, optical resonator and so on. Finally, the main applications and progress of discharge-pumped excimer laser in industry, medical treatment, scientific research, and other fields are introduced, as well as some unique key technologies.

A coherent spectrum analysis scheme based on a coherent receiver is proposed. The coherent receiver is used to perform in-phase and quadrature (IQ) mixing and balanced detection of the signal under test and optical local oscillator. The power of the signal under test is calculated according to the optical heterodyne principle, and the spectrum of the signal under test is reconstructed according to the mapping relationship between the calculated power and the corresponding frequency of the optical local oscillator. The experimental results show that the resolution is above 12.5 MHz when the sweeping rate of the optical local oscillator is in the range of 80-200 nm/s. The proposed spectral analysis scheme has an ultrahigh resolution and can be used to rapidly extract the fine spectral structure of ultradense wavelength division multiplexing systems.

In this study, a reflective terahertz dual-band linear polarization converter based on a metasurface structure is proposed. It adopts a typical "sandwich" structure. The upper and lower layers are metal layers, and the middle layer is a dielectric layer. Efficient conversion of x-polarized waves to y-polarized waves is realized. The results show that the polarization conversion rate of the polarization converter can reach more than 90% in the frequency bands of 0.611?0.713 THz and 1.335?1.364 THz. In the frequency bands of 0.626?0.677 THz and 1.340?1.360 THz, the polarization conversion rate is close to 100%, and perfect linear polarization conversion is realized. Using the surface current distribution, its polarization switching mechanism is elucidated in detail. The polarization conversion rate calculated based on the interference model theory agrees well with the simulation value. The polarization converter has a simple structural design, is easy to process, and has broad application prospects in the fields of terahertz communication, imaging, and detection.

Because the gas Raman scattering signal is very weak, the application of laser Raman technology in gas detection is limited. This study presents a method for enhancing the Raman signal for gas detection using multiple reflections and increased pressure. The air under normal pressure is used as the component to be measured, and the air under normal temperature and pressure is compressed into a closed sample tank by a pressure pump. The pressure in the sample tank is maintained at 0.1 MPa, 0.2 MPa, 0.3 MPa,…,1 MPa. The Raman spectral data of oxygen, nitrogen, and carbon dioxide in air (with wave numbers of characteristic peaks at 1552 cm-1, 2333 cm-1, and 1278 cm-1/1386 cm-1, respectively) are collected under the conditions of 10 different pressures and an integration time of 1 s. Variations in the characteristic peak with pressure are analyzed according to the four parameters of peak intensity, peak area, signal-to-noise ratio, and half-peak width. Results show that the signal-to-noise ratio is positively correlated with the pressure, which basically conforms to the logarithmic relationship. The signal-to-noise ratio increases by approximately 21 dB when the pressure increases from 0.1 MPa to 1 MPa. The peak intensity and peak area are positively correlated with the pressure and conform to the linear relationship. The central position of the characteristic peak is practically unrelated to the pressure, and the half-peak width changes little with pressure. Compared with the data of 1 MPa and 0.1 MPa, results also show that the oxygen characteristic peak expands to approximately 0.7 cm-1. Therefore, increasing the gas pressure is a simple and effective means of enhancing the Raman signal. The Raman signal can be further enhanced based on multiple reflections.