The fundamental structure of all-optical dual-hop free-space optical communication (FSO) system is presented and the composite fading channel model which includes atmospheric loss, atmospheric turbulence and pointing errors is established. In the full channel state information relaying, subcarrier intensity modulation is adopted. The closed-form expressions for outage probability and bit-error rate (BER) of dual-hop FSO systems are derived, based on the effects of background noise and amplified spontaneous emission noise. Then the outage probability of dual-hop FSO system is compared with that of the direct link. The effects of the parameters, such as signal-to-noise ratio, the average transmitted photon count of the source node (SN) and optical degree-of-freedom, on the outage probability and bit-error rate are also researched. The results show that all-optical dual-hop relaying can significantly improve the performance of the systems.

Light trapping is one of the key issues to improve the light absorption and increase the efficiency of solar cells. The absorption of Si thin film solar cells with different structures of back reflector, such as metal Al grating, inverse opal structure three dimension photonic crystal (3D PC) and their combination are systematically researched by utilizing finite difference time domain (FDTD) method. The results show that metal grating back reflector can mainly enhance the absorption of infrared light for solar cells. When the metal grating with the structural parameters of period is 700 nm, height is 100 nm, and duty cycle is 0.7, the average absorption rate of the solar cells in wavelength range of 750~1200 nm can be improved by 45.4% via replacing metal Al back reflector. For Si thin-film solar cells with inverse opal structure 3D PC the back reflector, the optimal structural parameters of air medium sphere are that the air medium sphere radium is 150 nm and the number of layers is 2. Compared to the metal Al back reflector,the average absorption rate of solar cells with 3D PC in wavelength range of 750~1200 nm can be improved a relative amount of 34.8% . Solar cells with combined structure back reflector has the best light absorption in wavelength range of 300~1200 nm. Compared to the metal Al back reflector, the average absorption rate can be improved a relative amount of 32%, which is better than metal grating or 3D PC. Due to the excellent reflection characteristics of metal grating and photonic crystals, the transmitted light is reflected back to absorbing layer, so that it can be absorbed two or more times. So the absorption efficiency of Si thin-film solar cells can be improved greatly.

Subwavelength high contrast grating (SHCG) is considered as an optical resonator for understanding its resonant filtering mechanism clearly. The transmission spectrum of SHCG is investigated by employing temporal coupled mode theory. The calculated result is in good agreement with the simulation obtained by using the rigorous coupled-wave analysis method. In addition，the influence and mechanism of the filter′s transmittance on incident angle，grating width and temperature are also investigated, respectively. The simulated results show that the spectrum linewidth of SHCG filter is mainly controlled by the incident angle. However, the spectrum linewidth is insensitive to the minor change of the grating width and the operating temperature.

A sensing method of refractive index based on single-mode-multimode-single-mode fiber structure is proposed. The sensor sensitivity is increased through valley detection method. It shows that number of pattern in the multimode fiber has vital influences on the transmission result. When the structure parameters of single-mode fiber and multimode fiber change and normalized frequency remains, the number of pattern of multimode fiber remains, and the regular transmission curve can be acquired. The sensitivity can be improved effectively with the increase of diameter of multimode fiber. The maximum sensitivity is 3.725×105 nm/RIU and the detection limit is 7×10-7 RIU, when the diameter of multimode fiber is 70 μm. When the actual length of multimode fiber is deviating from the design, the length of the deviation has little effect on the sensor sensitivity and detection limit, the output spectrum shift is -0.07 nm/μm, which means it can be practiced in high sensitive stress sensing.

In order to solve the energy distribution of the skewed normal distribution problems in the actual star imaging process, and improve the positioning accuracy of star point center, a point spread function (PSF) correlation algorithm based on skewed normal distribution is presented. The proposed algorithm establishes the corresponding PSF according to the energy distribution of actual star point. It uses the relevant principles to find the PSF with the highest similarity with star energy distribution, and then by determining the corresponding PSF maximum position to realize the positioning of the central star. The experimental results show that under the simulating condition of star image Gaussian noise in N(0,0.001)and the star center random distribution within 1 pixel, the average positioning accuracy of skewed normal distribution PSF correlation method can reach 0.04 pixel, which is far less than 0.4 pixel from the centroid method and 1.03 pixel from the Gaussian surface fitting method. Experimental results show that the proposed algorithm is better than the centroid method and Gaussian surface fitting method, which has good anti-noise performance and stability, and improves the positioning accuracy of the star center.

A method for phase recovery from undersampled wrapped phase is presented. The original undersampled wrapped phase is sheared once along horizontal or vertical direction, and then along the other different direction again. The obtained phase is unwrapped by the least-square algorithm. The required and unwrapped phase is obtained after iterative summation. Both the simulating and experimental results prove the validity of the improved method. The results show that the proposed method can not only vary the shearing direction and shearing times flexibly according to the undersampled wrapped phase to achieve the best result, but also retrieve the phase with high accuracy from the undersampled wrapped phase with weak noise.

To reveal comprehensive information and explore scientific methods for classification and provenance recognition of ancient Chinese blue and white porcelains, X-ray fluorescence (XRF) spectroscopy combined with optical coherence tomography (OCT) is used to study the glaze cross-section structure of blue and white porcelains excavated from the Nan′ao No. 1 shipwreck in the Ming dynasty of China. The characteristics of glaze cross-section structures and chemical compositions of glaze, body and cobalt pigment are obtained. The experimental results show that the blue and white porcelain samples originated from Jingdezhen and Zhangzhou are different in terms of glaze cross-section structure and chemical composition of glaze, body and cobalt pigment. According to the obvious difference of white glaze cross-section structures and chemical compositions of body and blue pigment, the blue and white porcelain samples originated from Zhangzhou can be divided into two types made by different kilns. In addition, the blue decorative pattern of blue and white porcelain samples originated from Jingdezhen is studied by three-dimensional scanning function of OCT, which indicates that the combination of OCT and XRF is validated as an effective method to study the classification, provenance and access to comprehensive information of ancient Chinese blue and white porcelains.

To improve the spatial resolution of X-ray real-time imaging systems, the optical micro-scanning technology is introduced into the existing imaging system and the optical micro-scanning X-ray real-time imaging system is built. The working principle of optical micro-scanning X-ray real-time imaging systems is introduced. The sub-pixel precision image registration technique is one of the key technology of successful application of the optical micro-scanning system. The principles, processes and concrete steps of frequency-domain windowing image registration method are introduced. Simulations with different registration algorithms for X-ray image are studied. Simulation results indicate indicate that the effectiveness of the image registration algorithm for X-ray image. The technique improves the accuracy of the actual X-ray image registration to a sub-pixel level and has a strong practical value.

In order to improve the target identification capability of the anti-tank missiles, the difference in polarization properties of the target and the background can be utilized to realize target detection and recognition.The intensity images and polarization images of the armored vehicles in four different environment backgrounds, such as no background, grass background, concrete background, and sandy background, are obtained by using the active laser polarization imaging technology. All these acquired intensity and polarization images are compared and analyzed in terms of edge intensity, image definition and spatial frequency, respectively. The results show that the polarization images have better edge and detail characteristics than the intensity images, which is conducive to the vehicle target recognition under complex background. The active laser polarization imaging technology will play an important role in promoting the target recognition capability of anti-tank missiles.

In order to realize the accurate superposition and seamless image assembly of interleaving assembly time delay integration (TDI) CCD imaging under the condition of large lateral swing space in spaceflight camera, it is mentioned in this paper that the number of the minimum overlap pixels can be calculated with the angle of image motion velocity vector among the dislocation lap joint pixels. First, velocity vector of ground object target in the coordinates of surface feature during satellite lateral swing imaging is analyzed. The velocity vector, latitude and longitude of harmony feature point are calculated using lateral swing angle. Then, the relationship of imaging and physical parameters have been projected to the image plane coordinates using the method of ray tracing and vector mapping. And then the angle between imaging velocity of overlap pixel has been calculated. Finally the least lap number pixel of two adjacent pieces TDI CCD is established by TDI CCD relationship. The algorithm is applied to the Fast Boat One satellite. By comparing the experimental and theoretical results, a deviation of pixels exists between actual and theoretical values in the image registration accuracy range. This method can effectively eliminate the large side swing imaging dislocation lap on pixel precision of stitching.

Workshop measuring and positioning system (wMPS) is a new kind of distributed coordinate measuring system based on photoelectric scanning. In order to further improve the dynamic coordinate measuring precision of wMPS, a brief introduction of wMPS dynamic coordinate measurement principle is presented. Based on the algorithm of extended Kalman filter (EKF), the model of uniform linear motion is established. Afterwards model and algorithm are simulated with computer. Based on the simulation results, the proposed method is verified experimentally, using ABB IRB 2400 industrial robot as the experiment platform. Experimental results indicate that the EKF algorithm can not only substitute the traditional least squares algorithm and estimate the trajectory, but also reduce the dynamic random errors in the measurement process and improve the system positioning accuracy. The proposed algorithm basically meets the requirements of industrial field measurement for dynamic object positioning.

In order to meet the demand of indoor location service, a new iterative closest point (ICP) algorithm based on K-means clustering is proposed to construct a structured two-dimensional indoor map. Based on the clustering analysis of the point cloud data obtained by the two dimensional laser scanner, the data of each frame is clustered, and the cloud data is pre-registered by the translation of the geometric center. The global optimal solution is obtained by the accuracy registration of the cloud data after clustering and pre-registering. Compared with the traditional ICP algorithm, the improved ICP algorithm can obtain higher accuracy registration results when the point cloud data is collected by a single 2D laser scanner. Experiments show that the algorithm has the advantages of strong robustness and high registration accuracy, which can help to construct the indoor map quickly and accurately under the single sensor.

The nonlinear errors theory in heterodyne interferometer is summarized, in which the formation mechanism, size and expressive form of first-order and second-order nonlinear errors are analyzed emphatically. The research progress of nonlinear error detection and compensation method is elaborated in detail, and the application characteristics of various methods are pointed out. It provides a theoretical foundation for further research on the nonlinearity to improve the accuracy of heterodyne interferometer.

Using the high-low temperature equipment, we study the influence of temperature on the transmission loss of the large-core optical fiber in the range of -100 ℃ to 100 ℃ by experiment. The experimental results show that the transmission loss coefficient at the first window (850 nm waveband) of the large-core optical fiber fluctuates randomly with temperature. The transmission loss coefficient in the whole temperature range is in the range of 2.543 dB/km to 4.237 dB/km. The results aslo show that, after high-low temperature cycle, the paramagnetic defects are not found in the optical fiber core and the cladding layer, therefore, the chemical bands of the fiber are not broken. In addition, the corresponding stress model is established to explain why the transmission loss coefficient fluctuates too much at the ends of high-low temperature, and the corresponding measures to reduce the effect of the temperature on transmission loss are proposed.

Research on defocus detection is an important issue in optical manufacture and testing. Astigmatism method is widely applied in the defocus detection due to the advantages of simple operation and high sensitivity. However, the design of defocus detection system based on astigmatism method is under improvement. The sensitivity analysis of the measurement system based on the basic theory of astigmatism method is carried on considering factors such as system components machinability and spot size rationality. The suitable parameters are determined and geometric parameters of optical components are optimized by the optical design software Zemax. The MATLAB is used for ray tracing to calculate the error caused by facular energy heterogeneity and non-standard elliptic property. Calibration of image plane with zero signal has been completed and the accuracy of measurement has been improved.

Major drawback of diode laser array is its asymmetric beam quality, which can be improved by beam shaping. Parallel glass plate arrays are used in beam shaping for single emitter of diode laser array based on its beam displacement property, which can reduce power loss in slow axis and adjust beam quality with high efficiency in both axes. Validated experiment based on a short diode laser array with 12 emitters is carried out, and the results indicate that the beam shaping effect is according with the simulation, and the beam shaping efficiency is 93.62%.

A chaotic modulation lidar for underwater ranging is proposed and demonstrated experimentally. The 532 nm chaotic laser is generated by a chaotic electrical signal produced by a Boolean chaotic circuit directly modulating the diode laser. It is divided into two beams as the probe light and the reference light signal, respectively. The probe light signal is injected into a water tank of 1.5 m×0.3 m×0.3 m to directly illuminate the underwater target. The probe light reflected from the target and the reference light are separately converted into the electrical signals by the photoelectric detector. The distance of the underwater target can be achieved by the cross-correlation between both of the electrical signals. Through the theoretical experiment demonstration, the minimum and maximum detection distance of 0.14 m and 1.36 m are obtained respectively. The range resolution is 51 cm and the average error of the target ranging results is within 2.3 cm. The chaotic lidar can be a new technology of underwater ranging owing to its essential characteristics of the small measuring blind area and the simple structure.

The experimental research regarding grooving and cutting the sapphire substrate by nanosecond laser with wavelength of 355 nm and picosecond laser with wavelength of 1064 nm is presented. The influence of adjusted processing parameters on the depth, width and quality of grooves via controlling the variable method is studied. Furthermore, the comparative analysis shows that the thermal effect of 355 nm nanosecond laser processing is very big, and the etching efficiency is low, which cannot achieve graphs cutting of sapphire substrate even if its peak power density reaches 109 W/cm2. However, 1064 nm picosecond infrared laser cutting quality of micro groove is very high, which can realize completely “cold” processing. Eventually, the results show that the graphs cutting on sapphire substrate can be realized with the laser peak power density of 1012 W/cm2, The high-quality graphs cutting on the blank of sapphire substrate with 0.55 mm thickness is realized by 1064 nm infrared laser with average power 1 W, single pulse energy 1 mJ, and pulse width 15 ps.

Based on the large-scale scene synthetic aperture radar (SAR) image series, a combined recognition and tracking method for various slowly-moving vehicle targets is presented. The method introduces an idea named recognition first and tracking later. A recognition algorithm combining local multi-resolution analysis for image target and multiple kernel classifier is studied, which realizes the high-speed feature extraction and accurate classification of various image targets. According to the corresponding relationship of targets in the adjacent frames, the targets′ motion parameters are estimated utilizing the unscented Kalman filter. Simultaneously, the real-time location and target type can be obtained via continuous correction using the measured values; as a result, high performance tracking of various slowly-moving ground targets in complicated background is realized. Large-scale scene SAR series images are constructed and several simulation tests are performed, demonstrating that the method has good convergence, excellent real-time performance, and high tracking precision.

Indium tin oxide (ITO), as a kind of transparent optic glass, is a highly degenerate semiconductor. The dielectric constant of ITO changes with incident wavelengths and is complex number. Ag-ITO-Ag waveguide is designed by ITO as dielectric layers. The transmission characteristics of electromagmetic waves in the structure of surface plasmon polariton (SPP) waveguide and the relevant characteristic parameters of SPP are obtained. In this structure, the expression of magnetic field distribution, SPP′s wavelength, propagation distance and dispersion equation are derived and the dispersion characteristic is researched. Besides, the relationship between group velocity and incident wavelength is studied. The effects of the thickness of dielectric layer on group velocity, different core mediums (ITO, air, SiO2) of the structure with same cladding layers (Ag) on group velocity and slow light effect are discussed. The results show that the Ag-ITO-Ag waveguide structure is more favorable for miniaturization and integration of photonic devices.

To detect the natural gas leakage of the pipeline underwater, a distributed optical fiber sensor system is introduced based on hybrid configuration of Sagnac/Mach-Zehnder interferometers. Based on time domain statistic features, the probability features of amplitude values distributed near the average can be extracted with time domain analysis of optical fiber interferometric signals. A principal components analysis model based on statistic features is established to monitor gas pipeline leakage condition. The squared prediction errors (SPE) statistics is used to discriminate pipeline condition, and compared to the traditional method of distributed optical fiber pipeline leakage detection which just depends on whether null frequency existing or not. The missing alarm rate (MAR) is calculated. The results show that the proposed time-domain statistical feature vector can describe the characteristics of pipeline condition, the SPE statistics in leakage condition can discriminate pipeline leakage accurately, and MAR decreases to about 1/10 of that with the traditional method based on null frequency.

The technology of optical millimeter-wave (MMW) generation based on four-wave mixing (FWM) effect has become a key research direction due to its various advantages like having no limitation on the signal frequency, amplitude and phase, and high optical conversion efficiency. This paper reviews the research history of the photonic generation technology of MMW based on FWM effect. Three technical routes for the photonic generation of MMW based on FWM effect are discussed, which include the utilization of semiconductor optical amplifier (SOA), highly nonlinear optical fiber (HNLF) and silicon waveguide. Research progress on chalcogenide glass fibers and chalcogenide waveguides for the photonic generation of MMW is reviewed. The development prospect for the photonic generation technology of MMW is also presented.

Low-pass spatial filtering for laser beams plays a key role in improving spatial quality of beams. With the development of high power laser beams, the traditional pinhole spatial filtering becomes a bottleneck to enhance the beam spatial quality, due to its focusing characteristics. Low-pass spatial filtering without focusing is an innovative technique, which can break the bottleneck and improve the spatial quality of beams. Volume grating, multi-layer film, Rugate coating, and photonic crystal have been the main techniques and research focuses to realize the non-focusing spatial filtering for laser beams because of their fine wave vector selectivity. Bragg diffraction of volume grating, constructive and destructive interference of multi-layer and Rugate coatings, and self-collimating of photonic crystal are described to analyze their spatial filtering performance, respectively. The research status of these four techniques for spatial filtering is reviewed. The four techniques can be a substitute for pinhole spatial filtering, especially in the field of high power laser beams.

Based on atomic emission spectrometry, laser-induced breakdown spectroscopy (LIBS) is a convenient and sensitive spectroscopic technique for the qualitative and quantitative element analysis. With the development of laser technique and spectrum analysis instrument, the technology and applications of LIBS have been rapidly developed. Beginning with the fundamental and working principle of the general LIBS, we present an overview of the recent progress of nanosecond LIBS in the technical development of portable and standoff systems and in its applications in environment monitoring, food safety, biological medicine, archaeology, space exploration and isotopic identification. The advantages of femtosecond LIBS and its recent applications are discussed. The principle and application progress of femtosecond laser filament induced breakdown spectroscopy are summarized.

The background and technical difficulties of infrared small target detection are introduced. Three types of small infrared target detection algorithms are summarized, such as spatial-domain filtering, transform-domain filtering and time-domain filtering. The common target detection method and edge segmentation method of spatial-domain filtering and transform-domain filtering are analyzed through experiments. Experimental results show that three types of small infrared target detection algorithms have both advantages and disadvantages. Selecting specific target detection algorithm is more affected by the target and background feature. And the development trend of small infrared target detection is discussed briefly.

Excessively high laser power density of the fiber core causes nonlinear effect and laser damage, which limits the output power enhancement of the fiber lasers. Using the multi-core fiber is one of the most effective schemes to solve this problem. The selection of in-phase supermode and the fabrication of multi-core fiber are the key factors for limiting the progress in multi-core fiber lasers. Therefore, how to realize a multi-core fiber with a large mode area and an in-phase supermode has attracted the attention of domestic and foreign researchers in recent years. The latest progress in mode selection and fabrication technology for multi-core fibers is illustrated, and the development prospect of realizing high power single-mode multi-core fiber lasers is proposed by evaluating the feasibility of several technical solutions.

Force and torque sensor is one of the most important external sensors for robots.With the development of special robots, it is becoming more and more important to research and develop a new type of force sensors that could be applied to special environment, such as minimally invasive surgery, nuclear magnetic resonance surgery, rescue and relief, nuclear power station, fire fighting, etc. As a special type of optical passive component, the fiber Bragg grating (FBG), taking light as sensing signal, is of prominent advantages, such as non-electric detection, immunity to electromagnetic noise, no zero drift, high precision, high temperature resistance,and the fact that multiple FBGs can be arrayed along a single fiber. Since FBGs was first used in robot multi-component force sensors in 2001, FBG based force/torque tactile sensing technology has been researched and applied widely. We describes the state of the art in multi-component force/torque sensing and tactile sensing technologies based on FBG, and presents the future work.

The new development of high power femtosecond fiber laser system is reviewed, including single femtosecond fiber chirped pulse amplification, spatially divided coherent beam combination, divided-pulse amplification coherent combination, nonlinear compression and spectral coherent beam combination, etc. The characteristics of these techniques are analyzed and it is pointed out that the coherent polarization beam combining technology based on active phase control is the most promising approach for developing high power femtosecond fiber laser system.

The steady-state temperature-dependent fluorescence of (Ba,Sr)2SiO4∶Eu2+ is studied, under an excitation at 405 nm. After the raise of two novel sensing methods, barycenter technique and intensity ratio technique for wide band emissions, multiple sensing functions are retrieved, using the behaviors of wavenumber/wavelength of emission band barycenter, emission bandwidth, and ratios of intensities at different wavelengths in the emission band, respectively. All the four kinds of functions demonstrate nearly linear relationship with temperature in the measurement range. The sensing mechanisms are briefly discussed. The phosphor′s multi-functional temperaturesensing abilities can be taken advantages of for use as a point thermometer for a variety of applications.

When the laser-induced breakdown spectroscopy (LIBS) is used for on-line quantitative analysis of liquid steel, matrix effect shows serious impact on the analysis accuracy. In the quantitative analysis, an improved multivariate nonlinear calibration method is used to reduce the matrix effect. The improved method is compared with univariate calibration and unimproved multivariate nonlinear calibration. The results show that the multivariate nonlinear calibration exhibits better accuracy compared with the univariate calibration method. The analytical performance is improved further after the multivariate model is improved. The fitting degree of calibration curves for measurement of Mn, Si elements increases from 0.980, 0.984 to 0.985, 0.989, respectively. The relative error for prediction of two validation samples decreases from 6.231%, 5.437% and 6.912%, 6.315% to 5.510%, 5.039% and 6.125%, 5.919%, respectively.

Fourier transform infrared spectroscopy (FTIR) combined with principal component analysis (PCA) and two-dimensional correlation infrared spectroscopy is applied to identify eight different varieties of Chinese rose leaves. The results show that the spectra of different varieties of rose leaves are similar, but there are obvious differences in second derivative spectra in the range of 1800~700 cm-1 which are selected to perform principal component analysis by SPSS software. The first three principal components have a cumulative contribution rate of 97.72% and yield classification accuracies of 95%. Two-dimensional correlation infrared spectroscopy is applied to study Chinese rose leaves. The significant differences in the position, intensity of auto-peaks and cross peaks are observed in the range of 1500~1275 cm-1and 1700~1520 cm-1. It is demonstrated that FTIR combined with principal component analysis and two-dimensional correlation infrared spectroscopy is a rapid and effective method for discriminating Chinese roses.

Heavy metal pollution is more and more serious in agriculture products. In the experiment, the rice polluted by cadmium is used as an example. We adopt coaxial dual pulse laser induced breakdown spectroscopy and the experimental parameters are optimized. The application of dual pulse-laser induced breakdown spectroscopy (DP-LIBS) in the area of monitoring the quality and safety of the farm products are explored. The feasibility of improving the sensitivity and accuracy for detecting the heavy metal in agricultural products is disscussed. The intensity of LIBS spectra and the real concentration of Cd of the nine concentration gradients samples are obtained by LIBS and anodic stripping voltammetry. By using univariate linear scaling regression model, three characteristic spectrum of Cd is analyzed quantitatively. The results indicate that the lowest mass fraction of Cd is detected by DP-LIBS with 5.03 μg/g and all the spectra lines have good correlation coefficients. The experiment shows that DP-LIBS can improve the detecting sensitivity and accuracy of Cd, its concentration information of Cd is got according to the linear regression model.

Signal analysis and pattern recognition methods for brain functional near-infrared spectroscopy (fNIRS) are especially important for its research and applications in the field of cognitive science. The traditional statistical feature extraction method for fNIRS is briefly reviewed and a new feature extraction method based on the principle of multivariate graph representation is proposed. The pattern recognition experiments based on both methods are conducted and compared. The experimental results indicate that the feature extraction method for fNIRS signals based on the multivariate graph representation principle can be used for signal analysis and visualization, which offers a new approach for the analysis of fNIRS signals.

Frame multispectral imaging technology is capable to acquire multi-band spectral images simultaneously, and has been widely used in many fields such as material analysis, environment monitoring and so on. A frame multispectral imaging method based on light field imaging technology is employed, and a secondary imaging system is designed to reimage the multispectral image obtained by the light field imaging system onto the photosensitive surface of detector. It is able to avoid the damage of detector caused by the direct contact between the microlens array and the photosensitive surface, and decrease the difficulty of adjustment and installation for the system as well. In addition, the factors that cause channel spectra aliasing are discussed. Based on the pixel gray matching method, the vector coordinates of each channel points are extracted and the spectral channel information is obtained. Besides, a series of plane calibrations under different light intensities are operated to get the normalized light throughput of every channel for calibrating the gray errors of the system. Eventually, an experimental system is set up, the multi-spectral instantaneous detection to indoor target is realized, and the clear recovered spectral images are obtained.

The theory of dynamic gas lock (DGL) suppression ratio is systematically studied and the DGL theoretical model is provided. Then the suppression ratio formulas of DGL with uniform or variable sections are derived through theoretical calculation under the conditions of single- or multi-component purge gases. Moreover, the suppression ratios of uniform-section DGL and variable-section DGL are compared for single-component purge gas. The theoretical results show that the uniform-section supposition, taking the section area where purge gas flows out DGL as the average section area, can be used when the suppression ratio is more than 85%; the suppression ratio is related to the DGL structure and the parameters of purge gas, and the suppression ratio increases with the increase of the gas volume flux into the wafer chamber when the DGL structure and diffusion coefficient are constant. The theory system proposed on DGL suppression ratio can provide a theoretical basis for the development of DGL in the extreme ultraviolet (EUV) lithography.