太赫兹离轴数字全息消零级方法的像质评价及其分析

Image Quality Evaluation and Analysis of Zero-Order Diffraction Elimination Method in Terahertz Off-Axis Digital Holography

在太赫兹离轴数字全息中,因其记录及再现距离较短,零级衍射会对再现像造成严重影响。利用三种图像质量客观评价指标,对2.52THz离轴数字全息中使用复振幅复原法和拉普拉斯算子消零级方法得到的再现像进行了比较分析。以成像实验中的分辨率板为模型设计了仿真目标,根据实验获得的照明光和参考光的强度分布仿真了全息图,利用角谱法进行再现,最后对真实太赫兹数字全息图进行了相同的处理,所得结果与仿真结论基本吻合。复振幅复原法和拉普拉斯算子法均能很好的抑制零级衍射。相比拉普拉斯算子法,复振幅复原法的零级衍射亮度衰减率更高,再现像整体上峰值信噪比更高,在高分辨率的0.2mm亮竖条纹区域具有更高的信噪比,图像质量更好。

In terahertz off-axis digital holography, the zero-order diffraction will still cause bad effects on the reconstructed image, as a result of short recording and reconstruction distance. Using three image quality objective evaluation indexes, the reconstructed images are compared and analyzed. The images are obtained by using the complex-wave retrieval method and the Laplacian operator method to eliminate the zero-order diffraction in 2.52 THz off-axis digital holography. Besides, the simulation target is designed with resolution chart in the actual imaging experiment. The hologram is simulated according to the intensity distribution of illumination light and reference light got from the real experiment, then the angular spectrum method is used to reconstruct the hologram. Finally, the corresponding processing is also performed to the hologram in the real terahertz digital holography experiment, and the results fit well with the simulation conclusions. Both methods have good suppression of zero- order diffraction. Compared with the Laplacian operator method, the complex-wave retrieval method has a higher brightness attenuation rate of zero-order diffraction, and the reconstructed image of it has higher peak signal to noise ratio overall. What＇s more, it has higher signal to noise ratio in 0.2 mm bright vertical stripe area with high resolution, and the image quality is better.