Design of a thermal imaging diagnostic using 90-degree off-axis parabolic mirrors
Design of a thermal imaging diagnostic using 90-degree off-axis parabolic mirrors
复制标题
使用90度离轴抛物面镜的热成像诊断设计
作者：
R. Malone;S. Becker;D. Dolan;R. Hacking;Randy Hickman;M. Kaufman;G. Stevens;W. Turley
对于冲击波实验来说，热成像是一项重要的、但具有挑战性的诊断方法。冲击压缩材料经历了标准(大于毫秒响应时间)红外探测器无法记录的瞬时温度变化。当实验附近的光学元件被摧毁时，会出现进一步的复杂情况。我们设计了一套热成像系统，用于研究桑迪亚国家实验室气枪内产生的冲击波温度。廉价的钻石抛物面反射镜通过蓝宝石真空端口将受冲击目标的图像传递到气枪室的外部。这幅图像的3000-5000 nm部分被对准红外相机，该相机以150 ns的最小曝光时间获取目标的快照。在最后一个中间图像平面插入特殊掩模，以在事件期间提供动态热背景记录。这幅图像的其他波长被分成高速探测器，分别工作在900-1700 nm和1700-3000 nm，用于时间分辨高温法测量。该系统结合了90度离轴抛物面反射镜，可以在宽光谱范围内收集低f/#光，以实现高速成像。必须使用匹配的镜对才能消除像差。为了消除像面倾斜，需要适当的抛物面反射镜的顶端到顶端的方向。如果一个抛物面反射镜绕连接这对抛物面反射镜的光轴旋转180度，得到的图像将倾斜60度。在不显著牺牲图像质量的情况下，不能使用不同的焦距反射镜来放大图像。本文对这种成像诊断的性能和像差进行了分析。
Thermal imaging is an important, though challenging, diagnostic for shockwave experiments. Shock-compressed materials undergo transient temperature changes that cannot be recorded with standard (greater than ms response time) infrared detectors. A further complication arises when optical elements near the experiment are destroyed. We have designed a thermal-imaging system for studying shock temperatures produced inside a gas gun at Sandia National Laboratories. Inexpensive, diamond-turned, parabolic mirrors relay an image of the shocked target to the exterior of the gas gun chamber through a sapphire vacuum port. The 3000-5000-nm portion of this image is directed to an infrared camera which acquires a snapshot of the target with a minimum exposure time of 150 ns. A special mask is inserted at the last intermediate image plane, to provide dynamic thermal background recording during the event. Other wavelength bands of this image are split into high-speed detectors operating at 900-1700 nm and at 1700-3000 nm, for time-resolved pyrometry measurements. This system incorporates 90-degree, off-axis parabolic mirrors, which can collect low f/# light over a broad spectral range, for high-speed imaging. Matched mirror pairs must be used so that aberrations cancel. To eliminate image plane tilt, proper tip-to-tip orientation of the parabolic mirrors is required. If one parabolic mirror is rotated 180 degrees about the optical axis connecting the pair of parabolic mirrors, the resulting image is tilted by 60 degrees. Different focal-length mirrors cannot be used to magnify the image without substantially sacrificing image quality. This paper analyzes performance and aberrations of this imaging diagnostic.