In order to ensure the accuracy and reliability of terahertz radiation intensity measurement, the responsivity calibration of pyroelectric terahertz detectors is carried out. First, a terahertz detector responsivity calibration device is constructed based on the substitution method, and the combined standard uncertainty of the device is 2.4%. Then, the 12D-3S-VP type terahertz detector is calibrated by the calibration device at the frequency point of 1.63 THz, and the responsivity calibration result is 197.6 mV/W, which is consistent with the value given by the manufacturer. The self-developed pyroelectric terahertz detector is calibrated, and the responsivity and the combined standard measurement uncertainty are 362.2 mV/W and 2.7% respectively. Finally, the standard deviation of the calibration result is compared with the combined standard uncertainty, and it is found that the standard deviation is in a reasonable range, which further proves the rationality of the calibration method, calibration results and uncertainty analysis.

Few-mode erbium-doped fiber amplifier (FM-EDFA) is a necessary repeater for long-haul mode division multiplexing (MDM) optical fiber communication systems, and its differential modal gain (DMG) directly affects the communication quality of the systems. In order to realize the gain equalization of different modes in FM-EDFA, a layered erbium ion doped ring core fiber supporting 4-mode group in cladding-pumped condition is proposed, and the pump mode is not considered. The ring core fiber is designed, and the DMG is reduced by controlling the change of the mode distribution induced by the central recess and outer groove refractive index of the core, combining with the well-designed doping radius and concentration of erbium ion. The results show that when erbium ions are doped in double layers in the ring core, the maximum DMG is reduced from 0.8 dB (single layer and uniform doping) to 0.44 dB (double layers in the ring core). In the full C band (1530--1565 nm), the gain of the 4-mode group is higher than 22 dB, the maximum DMG is less than 0.45 dB, and the noise figure is less than 5.3 dB. The cladding pump structure is conducive to the realization of all-fiber connection of FM-EDFA, is easy to integrate with MDM communication system, and gives full play to the all-optical compensation advantages of erbium-doped fiber amplifiers.

The output power of a 1550 nm erbium-ytterbium co-doped fiber amplifier at different temperatures and the output power and spectra after high-temperature aging are experimentally studied. By comparing the output power of the amplifier varying with the pump power at high temperatures and normal temperatures, we verified that when the erbium-ytterbium co-doped fiber amplifier works in a high temperature environment, the output power can be increased. The sensitivity of gain fibers of different lengths to temperature is different. Using the Arrhenius model as the accelerated aging model, the accelerated aging experiment was performed on the gain fiber at a temperature of 85 ℃ for 876 h. The results show that the output power of the erbium-ytterbium co-doped fiber amplifier will be reduced by 11.24% after working in a normal temperature environment for 5 years. The amplified spontaneous emission noise will increase by 4.1 dB, and the service life of the amplifier is predicted to be 7.57 years according to the exponential model, which provides the theoretical basis and experimental basis for improving the output performance and life prediction of fiber amplifiers.

Aiming at the multi-carrier filter bank transmission system for coherent optical offset quadrature amplitude modulation (CO-FBMC/OQAM) technique, a pilot-based time-domain phase noise compensation algorithm is proposed. A time-domain phase noise compensation model is established, that is, phase noise is approximated by time-domain extended discrete cosine transform (DCT). Phase noise includes common phase error (CPE) and non-CPE phase noise, which can be obtained by estimating DCT coefficients. In order to calculate these DCT coefficients, the CPE is estimated by pilot-based extended Kalman filter (EKF). Then, some of the data with high error probability after CPE compensation are discarded, and only the remaining CPE compensation data are retained for pre-decision to predict the sender data. Finally, the proposed algorithm is simulated and verified in a back-to-back CO-FBMC/OQAM system with a baud rate of 32 GBaud. The results show that compared with an improved phase search (M-BPS) algorithm, the spectral efficiency of the proposed algorithm decreases by 0.5%--2.0%. For 64-order QAM systems with subcarriers M=256 or 512, the linewidth delay product tolerance of the proposed algorithm is still much larger than that of the M-BPS algorithm, but its complexity is only half that of the M-BPS algorithm.

A multimode optical fiber communication system based on mode/mode group division multiplexing (MDM/MGDM) is one of the current research hotspots. Since there are multiple modes/mode groups multiplexed in the system, how to accurately recognize them is one of the key issues for improving the system performance. This article proposed an intelligent recognition model (IRM) of multimode fiber (MMF) supported fiber modes and mode groups based on the deep learning method through the introduction of a convolutional neural network (CNN). The theoretical simulation and experimental studies on the linear polarization (LP) modes and mode groups have been implemented under the influence of noise. Firstly, 10 LP modes (LP01, LP11a/b, LP21a/b, LP0, LP12a/b, and LP31a/b) and corresponding mode groups have been simulated and experimentally generated based on a customized multimode multi-plane light converter (MPLC) and a conventional OM2 MMF. Then a large amount of mode profiles can be obtained to train and test of the IRM. The experimental results show that the recognition rate of modes/mode groups can reach 100% by using the high-resolution mode images. Subsequently, we resized the high-resolution mode images into low-resolution ones, and the recognition performance of the intelligent recognition model under the receiving condition of a low density photodetector array is studied. Experimental results show that a recognition rate of 98.3% can be also realized when the light field information is received by a 4×4 photodetector array. Therefore, this research shows that the proposed intelligent recognition model can recognize the optical fiber modes/mode groups effectively. It also meant that this method has the potential applications in the MDM-based communication systems and intelligent optical performance monitoring.

Holographic stereogram (HS) is a kind of hologram that can accelerate calculation, which can realize the monochromatic holographic three-dimensional (3D) display, and combining it with the color rainbow hologram and realizing the half-circle viewable color rainbow holographic 3D display which can be watched by many people have practical application value. Based on the HS calculation principle, the side angle of view and the field of view of the elemental hologram are designed, and the spectrum of the elemental hologram containing red, green, and blue information through frequency domain multiplexing is achieved. The elemental hologram is obtained by taking the real part of the complex amplitude from the inverse Fourier transform of the spectrum. The high-resolution half-circle viewable color rainbow HS can be achieved by combining all elemental holograms. A high resolution half-circle viewable color rainbow HS with a resolution of 200800 pixel×200800 pixel and a size of 64 mm×64 mm is calculated only within 15.15 min by parallel acceleration. Reflective illumination is used for optical reproduction and a clear color holographic 3D display that can be viewed by multiple people is achieved, which is expected to be applied to 3D military maps, 3D sand tables, and other fields.

Due to the absorption of seawater and the scattering of suspended particles in water, the deep-sea image obtained by underwater robot through artificial light source is generally fuzzy, color deviation, and low resolution. Focusing on the key problems to be solved in the rapid and accurate restoration of deep-sea images, the data set of real deep-sea images is firstly established, and the imaging characteristics of deep-sea images are analyzed. Based on the statistical results of image features, a linear depth of field model is proposed. Then, the model parameters are identified by supervised method. Finally, according to the depth of field model, the transmission map and background light of the original image are estimated quickly, so as to effectively avoid cumulative error and achieve effective restoration of deep-sea images. Experimental results show that the proposed algorithm is superior to other algorithms in terms of image restoration results, validity, quality, and real-time performance. Processing 600 pixel×800 pixel image on Nvidia Jetson TX2 embedded device, the average restoration speed of the proposed algorithm is 3.08 times faster than the four outstanding underwater image enhancement algorithms.

The imaging quality of the optical system in an aerial camera is significantly affected by the accuracy of focal plane detection. To resolve the focusing problem of aerial cameras, a focusing algorithm based on multiple differential filtering effects is proposed. First, the principle of focusing is expounded. With the basic rectangular filter as the design basis, a new filter suitable for focusing of aerial cameras is proposed to eliminate the influence of the relative displacement between the image and the filter, and its feasibility is proved from a mathematical point of view. Then, the filter is simulated by interlaced sampling of the image to complete the design of the image focusing algorithm. Finally, the images collected in the experiment are used to evaluate the focusing effect of this algorithm. The experimental results show that the proposed algorithm can eliminate the sinusoidal change caused by the relative displacement between the rectangular filter and the image. The proposed algorithm is able to meet engineering requirements with high sensitivity and a maximum error of 41.16 μm, which is smaller than the half focal depth (76.8 μm) of the optical system.

A terahertz nondestructive testing imaging system with frequency modulated continuous wave is developed based on all-solid-state electronic devices and the zero intermediate frequency mechanism. The effective frequency range of the proposed system is 9.375--13.75 GHz, and the frequency ranges from 0.225 to 0.330 THz after frequency multiplication by a factor of 24 in the free space. A single horn antenna is combined with a directional coupler to achieve transceiver integration, and the terahertz beam is collimated and focused using a pair of lenses. The beam quality of the quasi-optical system is optimized and the signal-to-noise ratio of the system is improved, by which the best spatial resolution is ensured under current parameters. At the same time, nonlinear correction of the system is carried out by the phase focusing method so that the depth resolution is close to the theoretical resolution. Combining rectilinear scanning and rotating scanning, the system is capable of acquiring three-dimensional data in the cylindrical coordinate system. The high voltage insulation terminal is tested and evaluated by the proposed system, and the full-view perspective image is reconstructed, which realizes the digital twin of the three-dimensional structure of the detected target in real space and image space. In addition, the proposed system can accurately display abnormal areas inside the insulation terminal, which is conducive to the intuitive evaluation of the internal state of a detected target, and thus can further meet the requirements of nondestructive testing in the industrial field.

Optical microlenses have important applications in optical imaging, signal detection, biosensing, and other fields. As existing solid microlenses have invariable focuses and are biologically incompatible, chloroplasts in cells are used as natural microlenses, and the focusing properties of chloroplast microlenses and the application of such microlens in optical imaging and signal detection are studied. The results show that chloroplast microlens can focus incident lights with different wavelengths. The optical force generated by optical tweezers can be leveraged to control the shapes of the chloroplasts, and thereby adjust the focal length of the chloroplast microlens. The focal length can be adjusted in the range of 15--45 μm. Due to their ability to focus light, chloroplast microlenses can be applied to the imaging of subwavelength structures and the enhancement of fluorescence signals. In the experiment, optical imaging of the grating structure with a linewidth of 200 nm and actin filaments inside cells, as well as detection and enhancement of the fluorescence signal of quantum dots are achieved by the chloroplast microlens.

It is necessary to convert geodetic coordinates into radar coordinates to obtain the true value of the target in the detection of radar measurement accuracy. First, the conversion method between geodetic coordinate system and radar coordinate system is introduced. Then, the coordinate transformation error is analyzed from the aspects of geodetic result measurement error, radar reference point selection error and radar due north calibration error, and the error simulation results are given by using the actual measurement data of a continuous wave radar. Finally, the azimuth and origin correction method for improving the radar measurement accuracy is proposed. The application of the proposed method to the above continuous wave measurement radar can make the true value of the target more accurate, reduce the influence of coordinate conversion error on radar measurement accuracy obviously, and reflect the radar measurement accuracy more accurately.

In this paper, the theoretical simulation and experimental investigation are carried out on the gain coefficient process dependency of the advanced lithography focusing and leveling sensor. The theoretical model of gain coefficient process dependency was established to simulate and analyze the variations in the gain coefficient and measurement error of the focusing and leveling sensor with the film thickness of different materials for lithography process. The silicon wafers coated with SiO2 films of different thicknesses were tested in our self-developed experimental system. The experimental results of variations in the gain coefficient and the measurement error with the film thickness are consistent with the theoretical simulation results. Simulation and experimental results show that the process dependency measurement error of the focusing and leveling sensor has the peak values about 55.9 nm and 36.6 nm at the SiO2 film thicknesses of 250 nm and 690 nm, respectively. Using the silicon wafer coated with the specific film to calibrate the focusing and leveling sensor of the lithography machine can considerably reduce the effect of the gain coefficient process dependency and its measurement error. The investigation results of this paper can be used as reference to optimize the focusing control and lithography process.

To enable the stable operation of diode-pumped lasers without temperature control in a wide temperature range, the influence of the emission spectra of laser pump sources on the stability of laser systems is analyzed. Taking into account the energy utilization efficiency of the pumping process, an optimization scheme for the pump source spectra of lasers without temperature control is proposed. The scheme can effectively reduce the influence of the wavelength drift of pump sources on the absorption efficiency and thermal focal length of laser systems, thus making lasers work stably in a wide temperature range without temperature control. In the operating temperature range from -40 ℃ to 60 ℃, the optimal emission spectrum of a pump source is calculated for a Nd∶YAG laser system with different absorption lengths and doping concentrations (atomic number fractions). In theory, compared with a conventional single-wavelength laser diode (LD) pump sourse without temperature control, the pump source designed by this scheme can significantly improve the working stability of laser systems and reduce the fluctuations of absorption efficiency and thermal focal length to less than 13% and 16% respectively. A LD pump source with two wavelengths (803.7 nm@10 ℃ and 809.2 nm@10 ℃ with proportions of 68.4% and 31.6% respectively) is designed for the Nd∶YAG laser system with an absorption length of 30 mm and a doping concentration of 0.8%. The simulation results show that within the temperature range from -40 ℃ to 60 ℃, the absorption efficiency of pump light remains above 90.7%, and the absorption stability and thermal focal length stability are 91.4% and 85.4%, respectively.

Scattering is a fundamental phenomenon in nature. The imaging with large depth-of-field through a scattering medium is significant and valuable. In recent years, with the wide application of deep learning in computational imaging, it is urgent to study and further extend the depth-of-field in a scattering imaging system. In the paper, based on DenseNet and combined with the UNet architecture, a deep convolutional neural network model, namely DUNet, with good mobility and depth-of-field expansion ability is proposed. Moreover, the network is trained with speckle images passing through frosted glasses of different mesh, and the depth-of-field can be generalized to 50 mm away from the focal plane. The preliminary results on a rat brain slice demonstrate that the DUNet can be further implemented in the tomographic scanning of deep tissues.

A low-altitude sea surface infrared object detection method based on unsupervised domain adaptation is proposed. First, the source domain images are translated into target domain images by image translation network, and the labels are shared. Second, the gradient reversal layer is used in YOLOv5s object detection network to optimize the inter-domain adaptability of feature extraction. In addition, the maximum mean discrepancy loss is used to further narrow the feature distribution of different infrared detector images extracted from the network. Finally, AdamW asynchronous update optimization algorithm is adopted to further improve the training stability and detection accuracy. The proposed method is tested on low-altitude sea surface infrared ships and unmanned aerial vehicles collected by different infrared detectors. Experimental results show that compared with the traditional supervised learning method, the proposed method effectively reduces the cost of manual labeling, and detection accuracy of source domain and target domain are improved by 6.56 and 2.62 percentage points respectively, which effectively improves the generalization ability of the object detection model between different infrared detectors.

The alloy semiconductor material Mo1-XWXS2 (X is concentration) is prepared by hydrothermal synthesis method. The morphology and crystal structure of Mo1-XWXS2 are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy (Raman). The experimental results show that the surface of Mo1-XWXS2 alloy becomes rough with the increase of doping concentration by SEM morphology test. The XRD crystal structure shows that the lattice constant of Mo1-XWXS2 increases with the increase of doping concentration. In the Raman shift of the alloy material, with the increase of doping concentration, the A1g vibration mode in Mo1-XWXS2 has a blue shift, while the E2g1 vibration mode has a red shift. Through the detection and analysis of lattice structure and Raman frequency shift, it is proved that the hydrothermal synthesis method can prepare Mo1-XWXS2 alloy semiconductor materials with different concentrations. This method can be further extended to the batch preparation method of disulfide alloy semiconductor materials, which provides a basis for the fabrication and design of alloy semiconductor devices.

The number of atomic layers is an important parameter for wide band tunability of physical properties of black phosphorus. We theoretically investigate the two photon absorption coefficient in monolayer, bilayer, and trilayer black phosphorus and its dependence on the atomic layer number and polarization direction of the incident light based on the 5-hopping parameter continuous approximate model. The results show that the order of magnitude of the two-photon absorption coefficient of black phosphorus in armchair direction is 10 orders of magnitude larger than that in zigzag direction. The two-photon absorption coefficient of black phosphorus increases with the increase of the number of layers and the absorption peak has a red shift. Moreover, the two-photon absorption coefficient changes periodically with the polarization angle of the incident light as a cosine function. And the two-photon absorption coefficients of black phosphorus are the maximum when the polarization direction of the incident light is along the armchair direction, and the absorption coefficients decrease with the increase of the incidence angle. When the polarization direction is consistent with the zigzag direction, the absorption coefficient is smallest. This study provides a reliable theoretical guidance for the use of black phosphorus in photoelectric devices.

In view of traditional zoom lens cannot consistently and clearly image during the whole zoom process when the ambient temperature is changed, which needs to focus frequently at middle focal length position. This paper proposes a new design method which is named optical passive half-athermalization zoom lens design, and an optical passive half-athermalization zoom lens is designed by this novel method. The focal length of zoom lens is 30-1000 mm, spectrum wavelength is 486-656 nm, and F-number is F4.4-F8. Most importantly, the shortest focal length position of zoom lens is optical passive athermalization. The optical system has compact structure and excellent imaging quality, and based on method of passive half-athermalization design, optical system at any temperature between -40 ℃ and +60 ℃, which only need to focus once at the longest focal length position of zoom lens, that can ensure consistently and clearly image during the whole zoom process. There is no need to focus frequently in any middle zoom position, and the temperature adjustment of zoom lens is only -0.56-+0.82 mm, which have verified method of optical passive half-athermalization zoom lens design correctly. According to this method, zoom lens not only overcomes trouble of frequently focusing in traditional zoom lens, but also greatly reduces amount of temperature focusing and benefits on fast focusing.

Snapshot spectral imaging systems can obtain spectral images of moving targets in real time, and have urgent application requirements in the field of dynamic target tracking and recognition. The spectral and spatial resolutions of the snapshot spectral imaging system are mutually restricted. The existing snapshot spectral imaging system has a small numerical aperture, and it is difficult to achieve high spectral and spatial resolutions at the same time. This paper proposes a novel snapshot spectral imaging system based on the Dyson concentric structure. It has the advantages of large numerical aperture, excellent imaging performance, and compact structure. Meanwhile, through the off-axis of the field of view and complex design, the optical imaging performance is maintained while the space for mechanical assembly and adjustment is increased, which has good engineering feasibility. The optimized design of the novel snapshot spectral imaging system has a numerical aperture of 0.3, a spectral resolution better than 0.54 nm, and a spatial sampling point number of 112×24. This kind of high spectral and spatial resolution snapshot spectral imaging system can provide an important theoretical basis for the study of the snapshot spectral imaging system for the accurate detection and recognition of fast moving targets in a large field of view.

In order to correct the optical aberration in the varifocal process of flexible varifocal lens, a flexible varifocal lens with aberration correction function is proposed. The proposed lens consists of a varifocal module and an aberration correction module based on piezoelectric actuators. The principle prototype of the varifocal lens is fabricated and an experimental optical system is built to test it. The test results show that the proposed lens can achieve the refractive power variation of -1--5 D. The aberration correction module can accurately reconstruct 3~9 Zernike polynomial aberrations, and the normalized residual error is less than 4%. The aberrations of the system under different refractive powers are corrected, the wavefront aberrations of the corrected system are all decreased by more than 76%, and the imaging quality of the system is significantly improved.

In order to obtain organic light-emitting diodes OLEDs that can be used in plant lighting and have red and blue spectra, two typical carrier transport materials are used, N,N'-bis(1-naphthyl)-N,N'- Diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB) and 1,3,5-tris(1-phenyl-1 H-benzo[d]imidazole-2- TPBi forms a deep blue exciplex by interface contact or doping, and combines it with the red phosphorescent material Ir(DMP-IQ)2(acac), and the spectrum of the prepared OLED device meets the requirements of plant photosynthesis. By changing the thickness of the spacer layer between the deep blue exciplex complex and the red light emitting layer in the device structure, the blue/red light intensity ratio in the electroluminesence spectrum can be adjusted. On the basis of the structure of exciplex formed by doping, the host material (mCP) is incorporated into the NPB∶TPBi film to form a ternary system, which reduces the quenching of exciton caused by carrier accumulation in the film. Under the experimental conditions of a doping ratio of NPB∶TPBi∶mCP of 1∶1∶3, a turn-on voltage of 2.8 V, a brightness of 4528 cd/m 2, a current efficiency of 3.09 cd/A and an external quantum efficiency of 6.96% are obtained.

Beam wander causes power fluctuation and scintillation of optical vortex beams and is important in the fields of optical free space communication, sensing, and long-distance imaging. In this paper, beam wander of multi-mode vortex beams with incoherent superposition and coherent superposition is studied experimentally by controlling the multi-mode vortex states and simulated perturbations. After measuring the power fluctuation and scintillation index of orbital angular momentum (OAM) mode in the OAM spectrum, we find that the high-order vortex beams have a better anti-power-fluctuation and anti-scintillation performance than the low-order vortex beams; the multi-mode vortex beams perform better than the single-mode vortex beams; the incoherently superposed multi-mode high-order vortex beams perform better than the coherently superposed high-order multi-mode vortex beams. The comparison results show that the incoherently superimposed multi-mode high-order vortex beams have a best anti-scintillation and anti-power-fluctuation ability over other types of vortex beams, and might be suitable for the use in a beam wander disturbed environment. The results can be helpful for the application of vortex beams in the field of long-distance transmission and communication.

The determination of satellite clock offset is limited by the shot noise limit of classical measurement, and the accuracy of clock offset measurement is only on the order of ns. Based on the urgent demand for high-precision time reference in the military and civilian fields, a satellite clock offset measurement scheme based on dual-channel six-delay conveyor belt quantum entangled light is proposed, and the proposed scheme is based on the conveyor belt protocol. First, the frequency entangled optical signal is prepared by spontaneous parameter down-conversion. Then, the second-order correlation detection solution of the frequency entangled optical signal is carried out by using the HOM (Hong-Ou-Mandel) interferometer to obtain the clock offset information. Finally, the influence of related parameters on the clock offset measurement is simulated and analyzed. The proposed scheme does not need to measure the arrival time, is not affected by the dispersion effect and the distance between the satellite and the ground , and can theoretically realize satellite offset error measurement of the order of ps.

Because of the high cost and inconvenience caused by the need for a particular pump laser or heating resistor for the optical fiber thermal anemometer, a high-sensitivity optical fiber thermal anemometer based on the heating effect of the light source is proposed. First, the Fabry-Perot interferometer is made with ultraviolet curing glue on the end face of single-mode optical fiber and used as a sensing probe. Then, a higher initial temperature is obtained by using the heat absorbed by the sensor probe to the input broadband light source. Finally, the wavelength drift of the interference spectrum caused by the temperature drop and strain of the sensor probe under the action of air flow is measured, and the wind speed measurement is realized according to the specific relationship between the wavelength drift and the wind speed. The sensor is measured in the wind speed range from 0 to 7 m/s. The results show that the sensor achieves wind speed sensitivity up to -3.13 nm/(m·s -1), and the response time is about 250 ms.

Silver nanoparticles are grown on the surface of TiO2 nanorods by ultraviolet irradiation and used as surface-enhanced Raman scattering substrate. The effect of ultraviolet irradiation time on Raman sensitivity is studied, and samples of TiO2 nanorods/silver composite structure are prepared under different irradiation time. COMSOL Multiphysics simulation software is used to calculate the electromagnetic distribution and theoretical enhancement factors on the surface of TiO2 nanorods/silver composite structure. The experimental results show that the detection concentration of rhodamine is lower than 10 -10 mol/L and the maximum enhancement factor is about 1.84×10 8 after 10 min of ultraviolet irradiation, indicating that the substrate has good self-cleaning function.

Aiming at the problems that the linear dimension reduction method of three-dimensional (3D) fluorescence spectra of algae is not ideal and the model recognition accuracy is low, a classification model is constructed by using local linear embedding (LLE) algorithm to reduce the dimension and using the golden sine algorithm (Gold-SA) to optimize the support vector machine (SVM). The 3D fluorescence spectrum data of algae after dimension reduction by LLE algorithm is used as the input of SVM, and other two dimension reduction methods are compared. The results show that LLE algorithm has the best dimension reduction effect and the highest recognition accuracy. In order to further improve category recognition ability, the Gold-SA is used to optimize SVM and establish a Gold-SA-SVM model, and the other four classification models are compared. The results show that the classification recognition accuracy, precision, recall rate, and F1 score of the Gold-SA-SVM model are significantly improved, and the method can accurately realize the classification of Aureococcus anophagefferens, Chlorella, and Synechococcus elongatus, providing an effective reference for the research of brown tide.

The low absorption intensity of gas in the near infrared band is not conducive to the measurement of trace gas. A high-sensitivity and high-precision laser spectroscopy system for the simultaneous detection of atmospheric multi-component greenhouse gas was established based on the fundamental frequency absorption properties of molecules in the mid-infrared band, which uses a single novel room-temperature continuous-wave quantum cascaded laser (CW-QCL) combined with wavelength modulation spectroscopy (WMS) and a long-path optical-absorption cell. The output wavenumber of the system ranges from 2202.8 cm -1 to 2205.6 cm -1, covering the central absorption spectra of CO, N2O, and H2O. The results show that the measurement precisions of 1.83×10 -8, 1.86×10 -9, and 1.19×10 -4 for CO, N2O, and H2O, respectively, at 1 s time resolution. The minimum detection limits of the system can be further improved to 1.8×10 -9 for CO, 0.16×10 -9 for N2O, and 1.5×10 -5 for H2O by increasing optimal integration time to 100 s. The long-time measurement and analysis show that this system is simple in components, easy to use, and suitable for long time measurement of atmospheric multi-component gas. It can be widely used in the fields of atmospheric chemistry and greenhouse gas for highly sensitive detection research.

The transmission spectrum regarding the vertical incidence of a linearly polarized plane wave on the circular hole array on a submicron metal film is investigated. The maximum transmittance after the optimization of structural parameters is up to 0.896, which is much higher than the hole-filling ratio of the circular hole array, breaking through the expectation of traditional theories. After the analysis of the electric field distribution, waveguide mode, phase characteristics and dispersion relationship of the circular hole array on the metal film, the extraordinary transmission mechanism based on the circular hole waveguide on the metal film is investigated. A two-dimensional (2D) periodic optical lattice is formed above the circular hole array on the metal film due to the surface Bloch wave, and the electric field distribution center of the optical lattice is just above the circular hole part of the metal film. When the electric field mode of the optical lattice matches the transverse intrinsic electric field mode in the circular hole, the coupling efficiency will be large. If the phase matching condition is satisfied when the electric field mode propagates along the circular hole, the light in the circular hole can be effectively coupled from the circular hole, which thus generates a large transmittance. This mechanism can not only explain the extraordinary transmission phenomenon of a thick 2D circular hole array on a metal film but also be applicable to terahertz bands. If the circular holes are filled with a medium having a large refractive index, a large transmittance can be achieved when the wavelength is much larger than the hole radius.

In this paper, a non-null interferometric measurement method of X-ray mirror is proposed, which can achieve high precision interferometric measurement of zero ratrace error without splicing. A high precision plane mirror is used to calibrate the ratrace error of the interference system in the full field of view. By dividing the aspherical mirror into several sub-apertures, each sub-aperture can be approximately regarded as a plane, so that the ratrace error corresponding to the sub-aperture can be found from the calibration database, and the ratrace error of the entire aspherical mirror can be obtained by simple matrix splicing. Taking the X-ray elliptic cylindrical mirror as an example, the ratrace error of the non-null interferometric surface shape of the X-ray elliptic cylindrical mirror is effectively calibrated. Compared with the splicing interferometric method, the results of the two methods are consistent, which confirms the correctness of the proposed method.