Abstract:Wet chemical etching of InAs-based InAs/Ga（As）Sb superlattice long wavelength infrared photodiodes was studied in this paper. The etching experiments using citric acid, orthophosphoric acid and hydrogen peroxide were carried out on InAs, GaSb bulk materials and InAs/Ga（As）Sb superlattices with different solution ratios. An optimized etching solution for the InAs-based superlattices has been obtained. The etched surface roughness is only 1 nm. InAs-based superlattice LWIR detectors with 50 % cut-off wavelength of 12 μm were fabricated. The photodetectors etched with optimized solution ratio show low surface leakage characteristic. At 81 K temperature, the surface resistivity ρ_Surface of the detector is 4.4 × 10³ Ωcm.

Abstract:Mn composition dependence of optical properties, especially interband electronic transition and band tail absorption behaviors, in Mn doped (Pb, Sr)TiO₃ (PST) films were investigated by transmittance spectroscopy. The optical parameters of Mn doped PST films in transparent region were evaluated by Cauchy model. The decrease of optical band gap and the expansion of the band tail states with the increasing of Mn dopant amount were observed. The shrinkage of optical band gap is attributed to lowering the bottom of conduction bands by Mn 3d orbitals and the decrease of lattice constant in Mn doped PST films. Meanwhile, the random occupation of Mn ion and the increase of oxygen vacancy after Mn doping are the main causes for the expansion of localized states in band tails.

Abstract:In this study, the photoluminescence spectra of InAs/GaAs quantum dots material with photonic crystals were investigated by laser diode excitation. The photonic crystals were fabricated in the material of InAs/GaAs quantum dots by laser holography and wet etching method. It was found that the spectra from quantum dots with photonic crystals appeared multi-peak structure; the enhancement and modification to the short-wavelength component were more pronounced than those to the long-wavelength components. The photoluminescence from InAs/GaAs quantum dots was modified by photonic crystals, and the emission from excited states was significantly enhanced.

Abstract:Based on the six-layered metal/dielectric film structure, a new 2D tungsten twin-cross-grating-based solar selective absorber （SSA） has been proposed to improve the optical absorption in the solar radiation region. The weighted average absorptivity before the cut-off wavelength is about 96.5%, and the calculated emissivity at 850 K is about 0.086. The mechanisms of high absorption in the solar region have been further analyzed by field intensity distribution in the SSA structure. The absorber also has the feature to be less polarization-dependent and broad angular-independent up to 50°, which satisfies the required conditions of the SSA device in applications.

Abstract:Large power microwave nonlinear effects on amplitude-phase controller chip were experimentally tested and theoretical analyzed. This chip had the typical application on Ka-band phased array radar (PAR) transmit/receive (T/R) modules. The test platform was built up by a solid source and a pulsed magnetron to generate large power Ka-band microwave. The degradation and destroy phenomenon were observed distinctly as the input power amplitudes were improved. The total-state phase characteristics and the degradation thresholds of the selected chip are obtained through a series of experimental tests. At last, the results are given by figures and the damage mechanism is theoretically analyzed.

Abstract:Aircraft identification is implemented on thermal images acquired from ground-to-air infrared cameras. SRC is proved to be an effective image classifier robust to noise, which is quite suitable for thermal image tasks. However, rotation invariance is challenging requirements in this task. To solve this issue, a method is proposed to compute the target main orientation firstly, then rotate the target to a reference direction. Secondly, an over-complete dictionary is learned from histogram of oriented gradient features of these rotated targets. Thirdly, a sparse representation model is introduced and the identification problem is converted to a l₁-minimization problem. Finally, different aircraft types are predicted based on an evaluation index, which is called residual error. To validate the aircraft identification method, a recorded infrared aircraft dataset is implemented in an airfield. Experimental results show that the proposed method achieves 98.3% accuracy, and recovers the identity beyond 80% accuracy even when the test images are corrupted at 50%.

Abstract:HgCdTe APD is one of the developing trends of third generation inferred FPA detectors. In this paper we report the result on a 1616 arrays of HgCdTe avalanche photodiode with 3.56 μm cutoff wavelength. The operability in gain exceeds 90% and relative gain dispersion is lower than 20%. NEPh is about 60 at 6 V bias with excess noise factor close to 1.2.

Abstract:To solve the problem of low luminescence efficiency caused by the surface oxidation of InAs nanowires, C₁₈H₃₈S and (NH₄)₂S were adopted to passivate zinc blende (ZB) InAs nanowires synthesized by chemical vapor deposition (CVD). Photoluminescence (PL) spectra of (before and after sulfide passivation) InAs nanowires were performed. The experimental results show that the PL emission efficiency of C₁₈H₃₈S and (NH₄)₂S passivated InAs nanowires are ~ 6 times and ~ 7 times higher than that of unpassivated InAs nanowires at 25 K, respectively, in addition, the PL of (NH₄)₂S passivation InAs nanowires is detected at room temperature, which provides a possibility for future InAs nanowires based middle infrared nanophoton devices.

Abstract:For avalanche photodiodes （APDs）, low operation voltage is required for integrated circuit stability and low power consumption. In this paper, a model for InAlAsSb separate absorption, charge, and multiplication （SACM） APD is established. To get higher gain at lower reversed bias voltage without sacrificing the operating voltage range, a high/low band gap multiplication layer is adopted. The effects of the thickness and doping concentration of the multiplication layer on the dark-current and the break-down voltage have been investigated. By optimization of the doping concentration, the break-down voltage and punch-through voltage can be decreased simultaneously.

Abstract:Limited by the flexibility of beam scheduling and receiving channel number, the range/azimuth two-dimensional (2D) scan is mainly used in the current diversity phased array radar for collision avoidance. Due to the lack of targets" height information, if there is a high/low target in front of the radar which does not affect the passage of the carrier, it will likely to cause false alarm. Aiming at this problem, this paper proposes an antenna layout and signal processing method based on the combination of MIMO and diversity phased array radar to realize the three-dimensional detection. Compared with the two-dimensional collision avoidance radar, this method can effectively realize 3D detection without increasing the number of radar receiving channels and the radar size. Compared with the 2D sparse array radar, the radar designed in this paper does not generate azimuth grating lobe, which is suitable for multi-target detection under complex background.

Abstract:Relative to the single-cavity gyrotrons operating in high-order mode, the coaxial cavity gyrotrons have the advantages of reducing mode competition, improving the stability of single mode operation and increasing the power capacity. Therefore, the coaxial cavity gyrotrons are more suitable for electron cyclotron resonance heating and electron cyclotron current driving in controlled thermonuclear fusion and attract much attention. The effects of structure parameters, electron beam parameters and ohmic losses on the beam-wave interaction of a coaxial cavity gyrotron operating at 170 GHz, mode were investigated in detail. Firstly, the mode selection of 170-GHz MW-class gyrotrons was analyzed and mode was chosen as the operating mode. Secondly, based on the time-dependent self-consistent nonlinear theory, a time-domain single-mode steady-state code was written to study the beam-wave interaction. The influences of the beam current, the magnetic field and the ohmic losses on the cavity walls were analyzed and the operating parameters were optimized. The simulation results show that when the voltage, the beam current and the axial guiding magnetic field are designed to be 65 kV, 68 A and 6.58 T, an output with 2.18 MW power and 49.23 % efficiency can be obtained, the peak ohmic loss density on the outer wall of the cavity is 1.94 kW/cm², and the peak ohmic loss density on the insert is less than 0.15 W/cm². The interaction efficiency decreases with the increase of electron velocity spread, and the output frequency shifts downward. The thickness of electron beam has similar effects on the interaction.

Abstract:A method for measuring internal stray radiation in thermal infrared spectrometer system was proposed in this paper, which is based on radiometric calibration of a detector and a thermal infrared spectrometer. The output response curves of detector and the spectrometer system to blackbody radiation energy of a single spectral channel are calibrated separately. Therefore, the internal stray radiation gray value and radiation flux value of the spectrometer can be obtained and the gray value and radiation flux of the internal stray radiation at different integration times and temperatures in the system can also be calculated. The proposed method was used to measure the internal stray radiation of an existing spectrometer, and comparative experiments were carried out. Results show that the error between the experimental results and the theoretical predicted values is less than 1%. The proposed method has high maneuverability and can be used to measure the proportion of internal stray radiation in total output DN value of the system, predict the influence of refrigeration on internal stray radiation of spectrometer, and measure the inhibition effect of other internal stray radiation suppression methods.

Abstract:Cryocooler plays an extremely important role in the field of infrared remote sensing. The normal operation and performance of the detector will be affected if the cryocooler breaks down. A new intelligent fault diagnosis method for cryocooler has been proposed based on wavelet packet transform, genetic algorithm and SVM for rubbing fault. First, wavelet transform is applied to the vibration signal, and the vibration signal is extracted in time domain. The evaluation factors of the combined feature set are calculated by using the distance evaluation technique, and the corresponding sensitive features are selected. Then, the parameters of SVM are optimized by genetic algorithm. Finally, the selected sensitive features are input into the optimized SVM to identify different machine operation states automatically. The effectiveness of the method is verified by the fault simulation test of the cryocooler. Experimental results show that this method can identify and locate the cryocooler rubbing fault accurately, and the accuracy is 95%.

Abstract:To further to improve the detection accuracy and real-time performance of infrared small target detection at sea, a new method based on weighted scene priors is introduced. Firstly, using the sparse characteristics of the target and the non-local self-correlation characteristics of the sea background, the target-background separation problem is modeled as a robust low-rank matrix recovery problem. Moreover, the prior information on sea background is added into the model by weighted nuclear norm to accelerate the decomposition of target and background images’ matrix in the algorithm. Finally, the alternating direction method of multipliers (A DMM) is introduced to further to accelerate the iteration speed of the solution. The experimental results show that the proposed algorithm can effectively improve the accuracy of target detection. The real-time performance of the algorithm is improved by 120% compared with the original algorithm.

Abstract:Aiming for long-distance optical detection of weak aerial targets, we in this paper propose a method of performance characterization and key indexes matching design for a space-based detection system. Firstly, we analyze the main factors that affect the optical detectability of weak targets under complex environment based on the full link of the space-based detection system, including scene clutter, spectral radiation scale and geometric scale of detection system, etc. We then combine the above influencing factors to establish a performance characterization model which represents the relationship between the image signal-to-noise ratio of target and the above-mentioned influencing factors, that is, the performance representation model of the detection system. Finally, taking a typical detection scene as an example, by studying signal-to-noise ratio of target under different scene clutter and multi-scale coupling characteristics, the optimization of detection spectrum and its matching design with spatial resolution are proposed, which can provide theoretical basis and scientific guidance for the design of the space-based detection system, demonstration of system indexes and optimization of information processing algorithms.

Abstract:The Geostationary Interferometric Infrared Sounder （GIIRS） on board FY-4A is an infrared Fourier transform spectrometer. The primary use of GIIRS is to support numerical weather predictions by providing improved temperature and water vapor profile information, which requires high radiometric precision and accuracy. To meet the requirement, post-launch GIIRS calibration and validation activities were carried out. The spectral calibration has been done through determining the effective sampling frequency which is to take advantage of gaseous line center positions known to high accuracy. The radiometric calibration has been performed through using observation of hot and cold black body reference sources as the basis for two-point calibrations at each wavenumber. The amplitude of some spectrum bands was reduced, which may be caused by some materials gradually releasing a little gas. The estimated absolute spectral calibration uncertainty is 10 ppm, and the mean brightness temperature differences between GIIRS observations and IASI observations are all less than 1 K in the long-wave and mid-wave band.

Abstract:Controlling the propagation of terahertz (THz) wave is very important in the application of THz technology. THz modulator is considered to be the key device in next-generation THz wireless communication. A new-type optically pumped THz modulator based on Si-grown monolayer tungsten disulfide (WS₂) was demonstrated. WS₂ acts as a catalyst due to the formation of heterojunction at the junction between Si substrate and WS₂, since more carriers are catalyzed at the heterojunction under pumping power, the modulator can achieve more deep modulation depth. The result shows that the modulation depth of this Si-grown monolayer WS₂ modulator can reach 63.6% under the low pumping power of 117 mW and the wavelength of the pump light is 660 nm. This novel two-dimensional transition metal dichalcogenides with high modulation efficiency have a great prospect in the application of THz technology.

Abstract:This paper derived time domain multimode formula and combined it with the frequency single mode theory to investigate mode oscillation and mode interaction of a 394 GHz gyrotron. The gyrotron reaches a steady state where both and modes oscillate at 393.87 GHz in time domain theory while cannot oscillate in frequency domain theory when the beam voltage is 15 kV, the magnetic field is 7.185 T, and beam current is 0.25A. mode dominates the final oscillation, which output power and efficiency are 136.8 W and 3.6%, respectively. The output characteristics of the operating mode obtained by two theories are identical.

Abstract:This paper presents the design method and test results of a 910 nm high peak power vertical-cavity surface- emitting laser (VCSEL) array. More than 2 W output power was achieved for 910 nm VCSEL array under the Quasi-CW driving current. Under the electric pulsed driving condition with a repetition frequency of 10 kHz and a pulse width of 30 ns, the peak output power of a single VCSEL array reached 25.5 W at 60 A operating current. With the increase of operating current, the laser spectrum outputted by VCSEL array shows obvious broadening phenomenon, which proves that the large current drive of VCSEL array will still produce serious internal thermal effect even at the operation of narrow pulse. When the driving current increases to 60 A, the pulse width of the laser pulse waveform of VCSEL array only widens by about 6 ns. This proves that VCSEL array has A very superior impulse response characteristic. After beam collimation of VCSEL array, nearly circular uniform spot was obtained at a distance of 1 m. We believe that this kind of high power 910 nm array light source has great application potential in the future intelligent driving fields such as vehicle light detection and ranging (LiDAR).

Abstract:To detect the large-scale vessel targets in the whole day, all-weather and concealed, the synthesis aperture microwave radiometers with high resolution are proposed for the first time as a space-borne microwave thermal radiation passive detection system, which is used to detect the vessel targets on the sea. A novel method is proposed to quantitatively evaluate the detection capability of a space-borne microwave passive detection system. The relationship between system’s main specifications, the microwave radiation cross section of the target and the detection distance is established. The detection probability and the detection distance are derived, respectively. Simulation analysis and air-borne experiments are also carried out. Both simulation and experimentalresults demonstrate the feasibility of the space-borne synthesis aperture microwave thermal radiation passive detection technology with high resolution to detect the large-scale vessel targets. The synthesis aperture microwave radiometers with high resolution can be used as an important complementary system for space-based warning.