【作者】 刘琳；

【导师】 薛鸣球；

【作者基本信息】 苏州大学 ， 光学工程， 2010， 博士

【摘要】 非制冷热成像技术是当前红外热成像技术的重要发展方向之一。基于非制冷探测器发展低成本、用于高温事件探测的中波红外热成像系统具有广泛的应用前景。非制冷探测器具有重量轻、体积小、功耗低、稳定性好等优点,但其辐射响应率低。针对中波红外非制冷探测器辐射响应率低的不足,本文开展大相对孔径中波红外光学系统的研究。研制出的大相对孔径光学系统具有成像质量好、适用环境温度范围宽、尺寸小、重量轻、结构紧凑的优点,适于作为微小卫星平台上的空间成像系统。本文首先提出论文所要研究的问题,介绍国内外非制冷红外成像系统的研究现状,指出开展本课题研究的意义和应用价值。第二章从探测地球表面高温事件的使用要求出发,结合当前中波红外非制冷探测器的性能,计算确定光学系统的焦距、相对孔径和视场角。进一步从光学系统基本参数出发,比较分析现有光学系统类型和结构型式,确定使用折射或折/衍混合匹兹伐物镜结构型式。第三章详细分析环境温度变化对红外光学系统成像质量的影响,指出在空间环境温度变化条件下,热离焦量远远超出了焦深范围,必须消除热差的影响。通过比较各种消热差的方法,选择了重量轻、无功耗、可靠性好的光学被动消热差方法,给出实现光学被动消热差需满足的一般关系式。第四章介绍消热差折射光学系统的设计。根据光学被动消热差和消色差条件,利用热差图选择折射光学系统材料和分配光焦度。指出在本课题系统参数的条件下,匹兹伐结构至少需要四块透镜才能得到满足消热差、消色差和光焦度要求的解。运用初级像差理论求解折射系统的初始结构,挑选高级球差较小的解作为初始结构并进行优化设计。第五章详细论述了消热差折/衍混合光学系统的设计。阐述衍射元件的热差和色差特性,表明衍射元件具有的特殊热差和色差性能,相当于一种特殊的红外材料。使用衍射元件几乎不增加系统的重量,在匹兹伐物镜的前组引入衍射元件能够减少一片大尺寸的折射透镜,减轻系统的总重。通过热差图确定折/衍混合系统的材料和光焦度分配。介绍了衍射元件的单色像差特性,运用初级像差理论求出折/衍混合系统的初始结构。对折/衍混合系统和折射系统的优化设计结果进行比较,折/衍混合系统具有总重量轻的突出优势。随后对折/衍混合结构系统的加工和装调公差进行优化分配,获得易于实现的设计结果。第六章介绍了金刚石单点车削技术加工光学非球面和衍射面的方法,成功完成了前表面为非球面、后表面为衍射面的锗的折/衍混合透镜的加工。设计了光机结构和装调方案,给出了研制结果。最后对整个光学系统的MTF进行了测试,测试结果表明系统不仅在常温状态下成像质量良好,并且在一定的温度变化范围内保持较稳定的成像质量。最后,对论文主要内容和创新点进行总结,指出下一步需要开展的工作。更多还原

【Abstract】 Low-cost infrared imager based on uncooled focal plane arrays is one of the most important developments in thermal imaging techniques. It has wide application prospect for remote sensing high temperature events. The uncooled detector has many advantages such as lightweight, compactness, low power, and excellent reliability, but its radiation responsitivity is low at present. To compensate for this drawback, it is necessary to use midwave IR optical system with large relative aperture. At the same time, the developed high speed objective, which is expected to use as a spaceborne imaging system of microsatellite, should have high quality image, good adaptability to environment temperature fluctuation, lightweight and compact structure.The issue studied in this dissertation is put forward at first. The development and state of art of IR thermal imager with uncooled detector is introduced and its significance is pointed out. In chapter two, according to the requirements of detecting terrestrial high temperature events and the performance of current MWIR uncooled detector, the basic parameters of its used optical system, such as the focal length, relative aperture and field of view, are determined. Through comparing and analyzing various typical objectives, both refractive and refractive-diffractive hybrid Petzval lens are chosen as its candidate structure.In chapter three, the effect of environmental temperature fluctuation on the imaging quality of optical system is analyzed. Since its thermal defocus, due to the change of its enviromental temperature, extends far beyond the focus depth, thermal aberrations must be cancelled out. Compared with other various athermalization methods, optical passive method is preferred and studed for its light weight, good reliability and no power dissipation. The general equation for optical passive athermalization is deduced.In chapter four, the design of athermalized refractive optical system is introduced. Based on the conditons of optical passive athermalization and achromatism, its optical material and power distribution is determined through athermal chart. It is pointed out that at least four refractive lenses are necessary for Petzval refractive lens to meet these conditions. Its initial structure parameters are obtained though its primary aberration analysis. Among the obtained initial structures, the structure which high order spherical aberration is relatively low is chosen and further optimized.In the fifth chapter, the athermalized refractive-diffractive hybrid optical system design is detailed. The thermal and chromatic characteristics of diffractive optical element are introduced. For its unique dispersion and thermal properties, it can be regarded to make from a special kind of infrared material. Use of diffractive optical element nearly does not increase any system weight. Through introducing a diffractive optical element in the front group of the Petzval objective, a piece of large size lens can be saved so that its weight decreases considerable. The optical material and power distribution of the hybrid system is determined also through the athermal chart. Its initial structure is solved according to its primary aberration. The optimized refractive-diffractive hybrid system has distinctive advantage in weight over the designed refractive system. Then the former’s manufacture and assembly tolerances are distributed optimally so that its implementation is faciliated.In the sixth chapter, how to fabricate aspheric and diffractive surfaces with single point diamond turning technique is introduced. And the hybrid germanium lens comprising of an aspherical and a diffractive surface is successively machined. The opto-mechanical structure and the alignment and assembly scheme of the objective are designed. The performance test and results of our developed objective are reported. Then, its modulation transfer function MTF is measured. It is demonstrated that the manufactured lens has high imaging quality under room temperature and also can maintain its stability within certain temperature range.Finally, the main work and the innovative points in this dissertation are summarized, and the further work is prospected.更多还原