Sjodahl Mikael, Amer Eynas
Appl Opt. 2018 May 10;57(14):3645-3652. doi: 10.1364/AO.57.003645.
The two techniques of lateral shear interferometry and speckle deflectometry are analyzed in a common optical system for their ability to measure phase gradient fields of a thin phase object. The optical system is designed to introduce a shear in the frequency domain of a telecentric imaging system that gives a sensitivity of both techniques in proportion to the defocus introduced. In this implementation, both techniques successfully measure the horizontal component of the phase gradient field. The response of both techniques scales linearly with the defocus distance, and the precision is comparative, with a random error in the order of a few rad/mm. It is further concluded that the precision of the two techniques relates to the transverse speckle size in opposite ways. While a large spatial coherence width, and correspondingly a large lateral speckle size, makes lateral shear interferometry less susceptible to defocus, a large lateral speckle size is detrimental for speckle correlation. The susceptibility for the magnitude of the defocus is larger for the lateral shear interferometry technique as compared to the speckle deflectometry technique. The two techniques provide the same type of information; however, there are a few fundamental differences. Lateral shear interferometry relies on a special hardware configuration in which the shear angle is intrinsically integrated into the system. The design of a system sensitive to both in-plane phase gradient components requires a more complex configuration and is not considered in this paper. Speckle deflectometry, on the other hand, requires no special hardware, and both components of the phase gradient field are given directly from the measured speckle deformation field.
在一个通用光学系统中，对横向剪切干涉测量法和散斑偏折测量法这两种技术进行了分析，以评估它们测量薄相位物体相位梯度场的能力。该光学系统旨在在远心成像系统的频域中引入剪切，这使得两种技术的灵敏度都与引入的离焦量成正比。在这种实现方式中，两种技术都成功测量了相位梯度场的水平分量。两种技术的响应都与离焦距离呈线性比例关系，并且精度相当，随机误差在几弧度/毫米的量级。进一步得出结论，这两种技术的精度与横向散斑尺寸的关系相反。虽然较大的空间相干宽度以及相应较大的横向散斑尺寸会使横向剪切干涉测量法对离焦不太敏感，但较大的横向散斑尺寸对散斑相关性是不利的。与散斑偏折测量法相比，横向剪切干涉测量法对离焦量大小的敏感度更高。这两种技术提供相同类型的信息；然而，存在一些根本差异。横向剪切干涉测量法依赖于一种特殊的硬件配置，其中剪切角本质上已集成到系统中。设计一个对平面内相位梯度分量都敏感的系统需要更复杂的配置，本文未对此进行考虑。另一方面，散斑偏折测量法不需要特殊硬件，相位梯度场的两个分量都直接从测量的散斑变形场中得出。
