折射/衍射红外光学系统的消热差设计

研究了衍射光学元件的温度效应以及混合光学系统的消热差设计方法 ,给出了视场4 .2°、冷光栏效率 10 0 %、温度范围在 - 30～ 70℃的红外折射 /衍射混合消热差系统的设计结果     

红外3.7～4.8 μm波段折射/衍射光学系统的消热差设计

研究了衍射光学元件在红外折射/衍射混合光学系统中的消热差特性并给出了具体设计实例,该系统工作波段为3.7～4.8 μm,全视场角为7.12°,满足100%冷光阑效率.系统仅采用硅和锗两种材料,设计结果表明,该系统在-50～100℃温度范围内不仅成像质量接近衍射极限,而且结构简单、体积小、质量轻,适用于像元尺寸为30 μm、像元数320×240的凝视焦平面阵列探测器.     

轻量化超宽温度折/衍混合红外热像仪光学系统设计

设计一个用于红外热像仪的轻量化超宽温中波折/衍混合红外热像仪光学系统。光学系统参数:工作波段为3.7 m～4.8 m,相对孔径为1/2,焦距为120 mm,全视场角为5.18,满足100 %冷光栏效率。采用三片式结构,使用硅和锗两种常用的红外材料,以及一个非球面和一个衍射面,系统实现了轻量化和超宽温度下工作。系统在-60℃～160℃温度范围内成像质量接近衍射极限,可供像元尺寸为30 m、像元数256256的凝视型中波红外探测器使用,可探测到2.3 km远的坦克目标。     

红外混合光学系统衍射效率的测量方法及其实现

简要介绍了二元光学器件衍射效率的理论计算方法,给出了一些衍射效率的测量方法,在此基础上设计了一套实用的衍射效率测试系统,并针对一个应用在3~5μm波段的具体红外混合光学系统进行了测试,给出了测试结果,此测试系统对红外混合光学系统的设计加工具有实际意义。     

红外折射-衍射混合光学系统的热差分析

分析了衍射光学元件在红外折射－衍射混合光学系统中的消热差特性,指出衍射光学本身对热差的贡献是微小的,但它的特殊色散特性却在红外折射－衍射混合光学系统设计中间接地以了消热差的作用。设计了适用于３～５μｍ波段的红外折射－衍射混合光学系统并进行了分析。     

8～14μm波段折衍混合红外光学系统的热补偿设计

大多数军用和空间光学仪器的工作环境温度变化范围都较大，温度变化时光学元件的曲率、厚度和间隔都将发生变化，同时元件基体材料的折射率及所在介质的折射率也将发生变化。由于红外光学材料的折射率温度系数dn／dT较大，环境温度对红外光学系统的影响显得尤为严重。因此在红外成像系统中不得不加入主动或被动补偿机构，以补偿温度变化造成像面移动所引起的系统性能的降低。利用衍射元件独特的温度特性实现红外光学系统热补偿设计的方法，设计了波段为8～14μm、视场为16。的折衍混合红外光学系统。该系统使用硒化锌和锗两种红外材料，在一40～60℃的温度范围内的成像质量接近衍射极限，并且体积小、结构简单，重量轻。     

红外折射/衍射超常温光学系统

设计了折射/衍射混合减热差红外光学系统,仅使用硅和锗两种材料.设计结果表明,此系统具有良好的减热差和校色差作用,在-80～200℃温度范围内不仅得到接近衍射极限的成像质量,而且结构简单,体积小,重量轻.     

中波红外折衍光学系统消热差设计与杂光分析

论述了红外折衍混合消热差光学系统的设计原理与方法,利用衍射光学元件特性进行消热差与色差,设计出工作波段为3.5μm~5.2μm、F数为2、焦距为100 mm、全视场角7,°具有100%冷屏效率的折衍混合消热差光学系统。对系统进行杂光分析,理想成像光线的像面辐照度为1.5×104W/m2,其他非成像光线的像面辐照度为2 W/m2。该系统在-50℃~80℃的温度范围内成像质量接近衍射极限,适用于像元尺寸为30μm、像元数320×256的致冷型红外焦平面阵列探测器。     

折射/谐衍射红外双波段成像光谱仪系统研究

为了获取足够的目标信息,充分利用中波红外和长波红外的光谱信息,建立了谐衍射中、长波红外超光谱成像系统.利用谐衍射元件独特的色散特性,将谐衍射透镜应用于中、长波红外超光谱成像系统中,使系统在中波红外3.7—4.8 μm和长波红外8—12 μm的2个红外大气窗口内获取数百个光谱图像.设计结果表明,中波红外波段,在18对线/mm处光学系统的调制传递函数(MTF)大于0.55,长波红外波段,在13对线/mm处光学系统的MTF大于0.5,光学系统的衍射环绕能,在中波红外波段30 μm半径范围内大于85%,在长波红外     

制冷型折衍混合双波段红外光学系统无热化设计

基于衍射元件的特殊成像性质,使用双层衍射元件进行双波段红外光学系统设计已成为研究热点。使用双层衍射元件能够有效提升宽波段的衍射效率,在简化系统结构的基础上提高像质。将红外成像系统设计为制冷型结构,能够消除背景噪声干扰,保证100%的冷光阑效率。基于带宽积分平均衍射效率最大化方法,设计了一款含有双层衍射元件的制冷型双波段红外光学成像系统,实现了在双波段红外和宽温度范围下的无热化设计。光学系统含有三片透镜,仅由两种材料组成,入瞳直径为80 mm,焦距为100 mm,F数为1.25,有效视场为6°,工作波段为3.7～4.8μm和8.0～12.0μm,工作环境温度为-40～60℃。分析结果表明,在整个温度范围内,在17 lp/mm截止频率处,双波段红外光学系统所有视场的调制传递函数分别高于0.78和0.59,同时双层衍射元件在红外双波段的带宽积分平均衍射效率分别为99.35%和98.73%,综合带宽积分平均衍射效率为99.04%。此光学系统的结构设计简单,成像质量好,在军事和商业应用中具有一定优势。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.