离轴抛物面镜像面扫描太赫兹光学设计

Optical design of THz image surface scanning with an off axis parabolic mirror

为了提高太赫兹成像速度,设计了一种像面扫描太赫兹快速成像系统。它为反射式单像素探测器成像,成像系统采用新设计的表面镀金的离轴抛物面镜结构以实现大口径、无遮拦、高反射率、高质量成像;反射成像系统光学设计F数为2.93,通光孔径为100 mm,视场为±1°,焦距为293.45 mm,成像窗尺寸为64 mm×64 mm,圆孔直径为2 mm,扫描采集16×16像素图像时间为0.1 min,32×32像素图像时间为0.42 min,64×64像素图像时间为1.7 min,空间分辨率为1 cm。扫描系统结合压缩传感成像理论采用新型像面扫描方法实现快速成像,在系统焦平面位置加入旋转多孔盘,对像面的图像进行太赫兹能量强度扫描,使用金属光锥收集能量到高莱探测器。利用压缩传感理论的特殊条件(采样数目与图像像素数相等)进行像面图像采集,然后利用正则归一化方程重构像面图像,该系统具有成像速度快、分辨率高、低成本、结构紧凑合理的优点。

In order to improve the THz imaging speed, an image surface scanning THz fast imaging system was designed. It was a single pixel imaging system basing on the reflection type. The system collected THz by an off axis parabolic mirror which was used to realize the imaging of large caliber,high transmittance, high quality imaging. The optical parameters of system were that F/# was 2.93, the aperture diameter was 120 mm, the field angle was ±1°, the focus length was 293.45 mm, the size of imaging window was 64 mm ×64 mm, the diameter of circular hole was 2 mm, the imaging speed of 16 ×16 pixels was 0.1 min, the imaging speed of 32 ×32 pixels was 0.47 min, the imaging speed of 64 ×64 pixls was 1.7 min, and the spatial resolution was 10 mm. The system combined with compressed sensing theory and image surface scanning theory realized the fast imaging property. A rotation plate with holes was inserted at image surface position, which scanned the THz intensity. Then a light cone was employed to collect energy to the Golay detector. The device output image by a special situation of compressed sensing theory that the sample number equaled to the image pixels. Sequentially, the regular least squares algorithm was used to reconstruct intensity distribution. The system has the property of high imaging speed and resolution, low costs, and small structure.