雷射光斑之原理、量測、與抑制方法

Theory, measurement, and suppression methods of laser speckles

徐巍峰(Wei-Feng Hsu)

《光學工程》 123期 (2013/10) Pp. 6-12

摘要

雷射光斑不僅出現在全像的重建影像，也常見於諸多同調影像中，這種隨機分布的亮暗斑點嚴重影響了影像的品質。本文先概略敘述雷射光斑的形成原因、理論模式、相關應用、和傳統削減光斑的方法，接著探討量測光斑的技巧和近年來以繞射光學元件抑制光斑的應用研究，最後，我們提出負相關光斑影像抑制光斑的方法，這種以空間光調變器取代移動擴散片的設計具有非常高的光斑抑制率。

關鍵字

雷射光斑 ； 同調成像 ； 光斑對比值 ； 繞射光學元件 ； 負相關光斑

並列摘要

Laser speckles occur not only in the images reconstructed from a hologram but also in many coherent images. The presence of speckles, a random granular appearance in images resulting from the interference of the coherent waves scattered from a rough object, degrades the image quality and leaves fine details irresolvable. In the paper, we first review the formation, the statistical model, relative applications, and conventional reduction methods of speckle. They are followed by the technical details of the measurement of speckle. We then present the application of diffractive optical elements to reduce the image speckles recently developed. Finally, we show the use of negatively correlated speckled images for speckle suppression. The method is implemented using a spatial light modulator which replaces the dynamical diffuser and is able to achieve high suppression ratio.

並列關鍵字

laser speckle ； coherent imaging ； speckle contrast ； diffractive optical element ； negatively correlated speckle