Abstract:The low intrinsic absorption and the existence of the inherent defects hamper the monoatomic layer graphene from being a high-performance photoelectric material, which leads to the strategy to form heterostructure by combining graphene with semiconductor materials. In this work, a graphene/GaAs heterostructure based photodetector has been designed and fabricated, in which the two-dimensional electron gas are enhanced to improve the photoresponse ability at the band of sub-millimeter and Terahertz (THz) wave ranging from 20 GHz to 0.12 THz. Under 25 GHz radiation, the responsivity of photodetector at room temperature (RT) reaches 20.6 V?W^-1, with the response time of 9.8 μs and the noise equivalent power (NEP) of 3.2×10¹⁰ W?Hz^-1/2 under a bias of 400 mV. At 0.12 THz, the responsivity is determined to be 4.6 V?W^-1, with the response time of 10 μs. And a NEP of 1.4×10^-9 W?Hz^-1/2 can be achieved under the bias of 400 mV. These results exhibit great application potential for the graphene/GaAs heterostructure based THz photodetectors.

Abstract:A wideband terahertz fourth-harmonic mixer with low local oscillator (LO) power requirement based on anti-parallel planar Schottky diodes is proposed. In order to realize best performances of the mixer, the relations between the parasitic elements of Schottky diodes and the mixer’s performances are analyzed. The main parameters of Schottky diodes are optimized to reduce the optimum LO power of the fourth-harmonic mixer. Measured results show that the conversion loss of the proposed mixer based on specialized diodes is 14.2 ~ 20 dB within a wide band from 340 to 490 GHz with optimal LO power of 7 mW, while the noise temperature is 4020~ 17100 K in this frequency range.

Abstract:The electromagnetic characteristics of the double confocal waveguide for a gyro-TWT is investigated in details. The eigenvalue and the field distribution of two kinds of steady-state modes in a double confocal waveguide, namely the superposition mode and the ring mode, are calculated with the scalar formulation of Huygens’ Principle, the theoretical results agree well with those from the commercial CST software. When the anti-phase superposition mode TE₀₆ mode is chosen as an operating mode in a gyro-TWT, the diffractive loss of the potential parasitic modes is far greater than that of the operating mode. It means that the potential parasitic modes can be suppressed by means of its own diffractive loss in a double confocal waveguide. The mode density in a double confocal waveguide is higher than that in a single confocal waveguide, but far lower than that in a cylindrical waveguide. Compared to the single confocal waveguide, a higher beam-wave interaction efficiency can be obtained in the double confocal waveguide for a gyro-TWT, it is an appropriate choice to choose a double confocal waveguide as the beam-wave interaction structure in a gyro-TWT.

Abstract:Breast cancer (BC) is one of the most common diseases in women. The accurate detection for BC is very important in clinical practice. In this paper, in-vivo breast cancer in a subcutaneous xenograft mouse was studied with the continuous-wave terahertz (THz) reflection imaging system at 2.52THz. The high reflection region in THz images of in-vivo subcutaneous xenograft mouse corresponded well to the tumor area in visible. The difference value of 15% between tumor and normal tissues was observed. For the gold standard, the tumor areas at different depths from the surface of skin in mouse model were obtained by hematoxylin and

Abstract:Light-control splitting ratio tunable Y-type Terahertz waves to beam splitter based on two-dimensional photonic crystal is proposed. In this scenario, the feature that coupling with line defects and the point defects of nonlinear polymer materials which have the third-order nonlinear Kerr effect is utilized. The performance of Terahertz waves splitter with tunable splitting ratio is studied by Plane Wave Method (PWM) and Finite-Difference Time-Domain (FDTD).The research results show that the Y-type Terahertz wave splitter with tunable splitting ratio of two output ports by changing the light intensity of the control light can be realized.This beam splitter which the transmittance reaches over 98% can achieve Terahertz waves splitting with a specific wavelength. At the same time, the additional loss is less than 0.087dB and the response time reaches the order for ps.The splitter with tunable splitting ratio will have broad application prospects in future Terahertz wave communication.

Abstract:A terahertz quasi-optical mode converter with wide bandwidth was studied and designed. The quasi-optical mode converter used Denisov launcher, which had high efficiency, and worked in TE_6,2 mode. It was used to realize mode conversion in gyrotron. As the parameters of Denisov launcher were the main factors affecting the broadband performance of quasi-optical mode converter, the optimal design of the radiator parameters could increase the bandwidth of the mode converter. Using the self-developed quasi-optical simulation program for simulation, the bandwidth of the mode converter can reach 2 GHz (center frequency 94 GHz).

Abstract:In this paper, a metamaterial waveguide with four square hole resonators based on Dirac semimetal layers is proposed in the 800~1100nm range. Four transmission peaks (70%, 61%, 72%, and 63%) are achieved at resonance wavelengths 842nm, 921nm, 1010nm, and 1061nm, respectively. These transmission peaks are originated from the interference effect of magnetic fields distributed in the main cavity and cavities 1, 2, 3, or 4. These transmission peaks can be enhanced and moved to shorter wavelengths through increasing the Fermi energy. The proposed metamaterial waveguide can be applied in nanoscale filter, switch, or refractive index sensor.

Abstract:Room temperature operation of infrared photon detectors will open up a wider range of applications. This article summarizes the room temperature performance and dark current mechanism of semiconductor devices from near infrared to long wavelength infrared. Different methods to suppress dark current including the design of the interband cascade structure of InAs/GaSb type Ⅱ superlattices and the nonequilibrium operation mode of HgCdTe to suppress the Auger process show unique advantages. These electronic structural designs, combined with the latest progress in subwavelength photonic structures to enhance light coupling and reduce dark current, hold the promise to achieve a high performance infrared imaging chip operating in room temperature in the near future.

Abstract:CdZnTe wafer is an ideal substrate for HgCdTe epitaxial thin films. In order to optimize the electrical contact performance of CdZnTe substrate， the Au/Cd composite electrode was prepared on p-type （111）B CdZnTe wafer （tellurium-rich surface） by vacuum evaporation and magnetron sputtering respectively. By means of contact adhesion test， the adhesion between Au/Cd electrode and CdZnTe substrate was studied. Rutherford Backscattering Spectrometry （RBS） was used to compare the element depth distribution of samples with different deposition methods. The effects of the two preparation processes on the ohmic contact characteristics of Au/Cd composite electrode and CdZnTe substrate were compared through the current-voltage （I-V） test， and the optimum preparation technology of composite electrode was obtained.

Abstract:As-received ZnSe crystal has been examined by cathodoluminescence spectroscopy ranging from 350nm to 850nm at room temperature for internal defects and inclusions. Two cathodoluminescence peaks of 462nm and 453nm were detected，of which the former was identified as intrinsic cathodoluminescence of ZnSe and the latter was caused by the crystal defect. The Zn:Se ratio of 6:4 was found by energy dispersive x-ray spectroscopy(EDS)，and the extrinsic cathodoluminescence peak of 453nm was attributed to additional Zn in excess of ZnSe stoichiometry.

Abstract:Stimulated Raman Scattering (SRS) effect is a key factor restricting the application of high power laser transmission over single mode fiber in long distance . Using 1550nm unpolarized continuous wave single-mode fiber laser as light source, stimulated Raman scattering phenomenon generated by 103km single-mode fiber transmission under different injected light power conditions is experimentally studied. Cascaded long-period fiber gratings are used to carry out stimulated Raman scattering suppression experiments, and corresponding theoretical analysis is carried out. A criterion for the effectiveness of fiber stimulated Raman scattering suppression is proposed. Experiments demonstrate the stimulated Raman scattering phenomenon and verify the effectiveness of cascaded long-period fiber gratings for the suppression of stimulated Raman scattering.

Abstract:Laser heterodyne spectroscopy has been widely used in greenhouse gas detection and laser atmospheric transmission in recent years, because of its high spectral resolution, simple structure and low cost. A laser heterodyne spectrum detection system using 3.66 μm DFB laser as local oscillator source is designed. The real-time and accurate measurements of water vapor absorption spectrum in the whole atmosphere are also realized. Furthermore, the signal-to-noise ratio after 12 averaging is 160.4, and the spectral resolution is 0.009 cm^-1. The average values of water vapor column concentration in Hefei on May 22 and 23 were 1549 ppmv and 1730 ppmv respectively. The analysis of correlationship indicated that Compared with EM27/SUN measured by Fourier Transform Spectrometer, the correlation is 0.895 and 0.819 respectively, and the deviation is 14.2% and 11.2% respectively. With the design and research of the system, the real-time measurements of the solar absorption spectrum of water vapor in the atmosphere and the precise inversions of water vapor column density are realized, which lays a foundation for more accurate detection and concentration inversion of the absorption spectrum of water vapor and its isotope HDO.

Abstract:As is known, response time of a MEMS infrared (IR) detector is usually measured using a complicated measurement system consisting of a blackbody radiation source, a chopper and a water-cooling apparatus. For such a system, both blocking and hollow patterns in the chopper have certain areas, which consume a certain part of time when the chopper spins at a certain frequency. In conventional measurements of response time, however, it is difficult to exclude the time consumed by a chopper, as a result, a large error is usually introduced into the system. To address such an issue, a response time measurement system for MEMS IR detectors using a fast-pulse laser as its radiation source is proposed in this work. Such a system is able to avoid extra time parameter being introduced by equipment . For a thermopile IR detector, response time measured based on traditional method is 14.46ms, while based on the newly established system, the response time is only 3.13ms. This indicates that the new method can perfectly avoid a 300% time error introduced by the traditional method.

Abstract:Soil moisture is the core component that links the earth"s surface water cycle, energy cycle and biogeochemical cycle, and it is also the key parameter to study the ecosystem in karst rocky desertification area. The aim of this study was to retrieve the soil moisture with multi-temporal Sentinel-1 C-band SAR data and observation equations were constructed by using the Alpha approximation model over karst rocky desertification area. The spatial and temporal variation characteristics and the error influencing factors of the soil moisture retrieval results were analyzed. It is found that the overall change trend of soil moisture in the observation period is highly consistent with the trend of rainfall change. The maximum value of soil moisture and the degree of spatial heterogeneity in karst rocky desertification area is significantly higher than those in non-rocky desertification area. The results were validated using ground measurements of one acquisition date, with root mean squared error （RMSE） value of 0.059 cm³/cm³ and mean bias value of 0.026 cm³/cm³. The method of retrieval of soil moisture by Alpha approximate model is applicable to karst rocky desertification area, the mixed pixel problem caused by the surrounding complex habitat conditions of the surface soil is the main influencing factor of inversion error. These results can provide reference to obtaining soil moisture under mountain complex environment by multi-temporal observation method, and provide support for ecosystem restoration and ecological industry development in karst rocky desertification area.

Abstract:The exploitation of mineral resources has promoted rapid economic growth, but it has also caused mining areas to have increased surface thermal flux, which has a negative impact on the ecological environment. In this study, using on Landsat satellite remote sensing images of the study area from 2000 to 2018, the radiative transfer equation method was used to invert Land Surface Temperature (LST). VFC in the study area was inverted based on the Normalized Difference Vegetation Index (NDVI)-Dry Fuel Index (DFI) three-component pixel model. Mixed pixels were decomposed into Photosynthetic Vegetation (PV), Non-Photosynthetic Vegetation (NPV), and Bare Soil (BS). Based on the four ecological parameters, Factional Cover of Photosynthetic Vegetation (f_PV), Normalized Difference Moisture Index (NDMI), Normalized Difference Built-up Index (NDBI), and Bare Soil Index (BSI), a remote sensing integrated ecological index (RSIEI) model which can comprehensively evaluate the differentiation effect of the surface thermal environment in mining intensive areas is proposed using Principal Component Analysis (PCA). The relationship between the differentiation effect of the surface thermal environment and the quality of the ecological environment was studied using the heat island variation index. The results showed that the NDVI-DFI feature space of the study area conforms to the basic assumption of the three-component pixel model. And the four ecological parameters are closely related to the differentiation effect of the surface thermal environment. From the regression equation of the four ecological parameters and LST in study area over three years, it can be seen that f_PV and NDMI has a significant linear negative correlation with LST (p<0.01); NDBI and BSI have a significant linear positive correlation with LST (p<0.01). The spatial distribution of normalized RSIEI images and normalized LST images of study area showed an inverse spatial correlation, i.e., the areas with high RSIEI (good ecological quality) in the study area correspond to the areas with low LST and vice versa. The quantitative regression analysis of RSIEI and LST in 3 years in 4 mining intensive areas shows that, when RSIEI is increased by 10%, LST was decreased by 0.67–0.77°C. It is proved that the RSIEI model based on Principal Component Analysis (PCA) is suitable for the comprehensive evaluation of the surface thermal environment differentiation effect in mining intensive areas.

Abstract:In the complex and changeable sea environment, when using infrared imaging technology to search and rescue small and medium targets on the sea surface, it is necessary to classify the collected original images in order to facilitate the subsequent target processing in different scenes. According to different environmental conditions, the sea infrared images are divided into five kinds of scenes. The training set images are extracted from two aspects: one is to divide an image into basic layer and detail layer by the Gaussian filter, and use improved histogram of oriented gradient (HOG) method to extract the features; the other is to extract features by calculating local contrast of images. The extracted feature vectors are fused and input into the classifier, and the test set images are classified by support vector machine (SVM). In this paper, a new feature descriptor combined with HOG and local contrast method (LCM) is used to classify the scene of sea infrared image. Compared with other methods, the results show that the accuracy of the improved method is 96.4%, which reflects the feasibility and effectiveness.

Abstract:The detection of the aerial targets applied on the space-based platform has the effects of long distance, weak signal of targets, complex background clutters and noises from detectors, therefore, it is extremely important to determine the bands, which might obtain the strongest signal, during the process of detection. The trapezoidal plume and the cone plume simulation model are systematically established, meanwhile an SNCR method combining the signal to noisy ratio（SNR） and the signal to clutter ratio（SCR） is proposed to determine the detection bands. The experimental result shows that, different aerial targets have different SNCR values, but with the same peak value. According to the method mentioned above, bands have been determined and eventually been determined the values as follows: in MWIR band, in which interval is not less than 0.3, in LWIR band, in which interval is not less than 0.3.