Design of midwave infrared athermalization optical system with a large focal plane array

Based on the most advanced staring focal plane array which had a format of 640 × 480 and the pixel pitch of 15 μm, a set of all-sphere midwave infrared ahermalization optical system was designed. The working wavelength was in 3–5 μm, the full field of view was 8.58°, the relative aperture was 1/2, the efficient focal length (EFL) was 80 m. The opticalsystem consisted of four lenses with three kinds of material – Ge, ZnSe and Si. All surfaces were sphere, which was easier to process test, making the cost inexpensive, and it could avoid using diffractive surface and aspheric surface. The image quality of the system approaches the diffraction limit in the temperature range −60 °C-180 °C. The design results proved that, the high resolution midwave infrared optical system had compact structure, small volume, high resolution and excellent image quality, meeting the design requirements, so that it could be used for photoelectric detection and tracking system.     

Morphological center operator for enhancing small target obtained by infrared imaging sensor

Infrared small target in image obtained by infrared imaging sensor is usually different from the surrounding regions, which is the important region in infrared image for different applications. However, the infrared small target is dim and embedded in clutter background, which makes the small target difficult to be detected or recognized. So, it is important to enhance infrared small target. Morphological center operator could smooth important image features, which may be well used for infrared small target enhancement. To well enhance infrared small target, a morphological center operator based method is proposed. The morphological center operator is specified to suppress most of the background of the infrared image through the strategy of feature extraction. Then, the infrared small target is well enhanced. Experimental results show that, the proposed method performs well for enhancing infrared small target and the performance is better than some other methods. So, the proposed method could further improve the performance of infrared imaging sensor.     

A novel accurate and expandable infrared radiation transmission effect computing service

In infrared imaging simulation system, the infrared radiation transmission is significantly affected by natural environment. Attenuation and blurring are introduced by atmospheric environment impacts on the transmission process from zero sight infrared radiation to the detector. The classic IR transmission calculation methods have been intensively studied and many applicable approaches are proposed. The novel IR transmission effect computing service introduced in this paper could render accurate and expandable IR simulation result based on synthetic natural environment, especially concerning the atmosphere effects imposed on the IR transmission process. A simulation architecture is constructed and supports an infrared imaging simulation system for the IR transmission process calculation. The environment representation approach and the transmission effect calculation method were elaborated. Simulation experiment was carried out and the result was shown to be more accurate than that of conventional MODTRAN based atmosphere transmission simulation results. The two results are both compared with the physically captured image. The comprehensive simulation experiment results are implied to be competent and offered an applicable solution for the infrared imaging simulation system. Furthermore, this interdisciplinary simulation method can be extended to other synthetic natural environment supported military simulation and further serve the large-scale distributed collaborative combat simulation.     

Fast image enhancement using multi-scale saliency extraction in infrared imagery

We propose a multi-scale saliency extraction based fast infrared image enhancement approach. A local frequency-tuned based saliency extraction technique is designed for highlighting the salient regions, firstly. Then, multi-scale saliency extraction is demonstrated, introducing multi-scale local windows with different sizes to extract regions of interest at different scales. Finally, the original image is enhanced with combining multi-scale salient image regions into one image. The experimental results prove the proposed approach is robust and efficient for infrared image enhancement.     

Synthesis,crystal growth and characterization of novel semiorganic nonlinear optical crystal: Dichloro(beta-alanine)cadmium(II)

Semiorganic nonlinear optical material of dichloro(beta-alanine)cadmium(II) (DCBAC) have been synthesized and single crystals were grown by solvent evaporation method at room temperature. The lattice parameters of the grown crystals are determined by single crystal XRD. The modes of vibration of different molecular groups present in the sample were identified by the FTIR spectral analysis. Thermal stability of the crystal was investigated using thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The dielectric constants of the crystal were studied as a function of frequency and the results are discussed. The grown crystals are subjected to microhardness studies and the variation of the microhardness with the applied load is studied. The optical transmission spectra and second harmonic generation (SHG) were investigated to study its linear and nonlinear optical properties. The nonlinear optical (NLO) property of the crystal was confirmed by powder second harmonic generation (SHG) test. SHG efficiency is comparable to that of KDP.     

Analysis of the features and reconstruction of a high resolution infrared image based on a multi-aperture imaging system

Infrared images of good quality are strictly important for such applications as targets detection, tracking and identifying. Traditional single aperture infrared imaging system brings in some defects for its imaging scheme. Multi-aperture imaging system shows promising characteristic of improving image quality and reducing size of optical instruments. We reconstruct a high resolution infrared image from the low resolution sub-images collected by the compact multi-aperture imaging system. A novel reconstruction method called pixels closely arrange (PCA) is proposed based on analyzing the compound eye imaging process, and this method is verified in a simulated 3D infrared scene to capture sub-images. An evaluation of the reconstructed image quality is presented to discuss the significant factors that affect the final result. Experimental results show that the PCA method can be efficiently applied to the multi-aperture infrared imaging system as long as the structure of the micro-lens array is specifically designed to be adaptive to the infrared focal plane array (IFPA).     

Study on infrared emissivity of biomimetic motheye sapphire single crystal

As a focus of research on materials science, bionic structure has drawn a great deal of attention from researchers. In this paper, patterned antireflection microstructure used for space optical window was fabricated on the surface of sapphire single crystal based on “Biomimetic Motheye Structure”. Meanwhile, emissivity of patterned sapphire at high temperature was investigated. The results indicated that transmittance of sapphire increased with spectrum red shift effect because of surface microstructures; the emissivity of patterned sapphire increased with rising of temperature in 6∼11 μm band; microstructures on surface led the scattering and attenuation coefficient of light to increase, thus, the emissivity of patterned sapphire was greater than that of contrast specimen which was not patterned. At the end of the paper, an audacious conclusion was made that the effect of microstructure on emissivity would decrease or even disappear with the increase of temperature.     

Aerodynamic heating of the dome on imaging quality degradation of conformal optical systems

The aerodynamic flow field surrounding the conformal dome was calculated. The thermal response of the aerodynamically heated conformal dome was analyzed. Gradient refractive index method was used to rebuild the non-uniform refractive index field of the conformal dome. Zernike polynomial fitting method was employed to establish the deformed surfaces of the conformal dome. Zernike aberration theory and modulation transfer function were adopted to evaluate the imaging quality of the conformal optical system. The results show that the aerodynamic heating of the dome severely affects the imaging quality of the conformal optical system.     

溴化苄及其阳离子红外光谱的理论研究

利用密度泛函理论（DFT）在B3LYP/6-311G++（d,p）水平上对溴化苄分子进行了结构优化和频率计算,得到了该分子的稳定构型和全部振动模式。计算得到的几何参数通过与苯分子的实验值相比,发现理论值与其相吻合;理论计算和实验测得的红外光谱数据的比较分析表明,理论计算与实验测量结果符合得较好,并对其振动模式进行了归属。最后,在B3LYP/6-311G++（d,p）水平上计算得到了溴化苄阳离子的红外光谱,并与溴化苄进行了比较,计算表明电离对振动偶极距产生了较大影响。     

Incident angle and temperature dependence of WSi wire-grid polarizer

The dependences of the incident angle and thermal durability of a tungsten silicide (WSi) wire-grid polarizer were examined. A WSi grating with a 0.5 fill factor, 260 nm depth, and 400 nm period was formed on a Si surface using two-beam interference and dry etching. The TM transmission spectrum of the fabricated element was greater than 60% at the incident angle of θ = 40° (the angle between the incident direction and the perpendicular axis to the grating direction) in the 4–10 μm wavelength range. An extinction ratio of 22.2 dB was achieved at 2.5 μm wavelength. Additionally, results show that this polarizer has higher thermal resistance than that of commercial infrared polarizers. Therefore, this polarizer is effective for taking a polarized thermal image of high temperatures.