Siavashani Morteza Jafari, Nasimdoust Elyas, Elahi Parviz, Tavassoly Mohammad Taghi, Moradi Ali-Reza
Department of Physics, Sharif University of Technology, Tehran, 11155-9161, Iran.
Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, 45137-66731, Iran.
Sci Rep. 2023 Aug 12;13(1):13155. doi: 10.1038/s41598-023-40267-6.
Optical diffractometry (OD) using a phase step is an alternative for interferometry, further, has least sensitivity to environmental vibrations. Therefore, OD has found numerous interesting metrological and technological applications. OD utilizes a phase step to detect the influence of objects under measurement by the changes in the Fresnel diffraction pattern. Recently, we showed that such measurements do not require infinitively sharp phase steps, although fabrication of such sharp elements is also impossible. Here, we address the issue of smoothness of the phase step surfaces. So far, in all of the OD applications the surfaces of the incorporated phase steps are considered to be optically smooth and flat. However, practically, some amount of roughness and unflatness is unavoidable even in precise and careful fabrication process. We show that preserving the OD-diffraction-pattern characteristics of a phase step depends on the level of roughness in the surfaces of the phase step. We define number of detectable fringes and autocorrelation functions of the diffraction patterns as the measures for evaluating the similarity of the rough phase step diffractions to the ideal case. We derive the theoretical description and confirm the results with simulations and experiments.
采用相位步进的光学衍射测量法（OD）是干涉测量法的一种替代方法，而且对环境振动的敏感度最低。因此，OD已在众多计量和技术应用中得到了广泛应用。OD利用相位步进，通过菲涅耳衍射图案的变化来检测被测物体的影响。最近，我们发现此类测量并不需要无限尖锐的相位步进，尽管制造这种尖锐元件也是不可能的。在此，我们探讨相位步进表面的平滑度问题。到目前为止，在所有OD应用中，所采用的相位步进表面都被视为光学平滑且平整的。然而，实际上，即使在精确且细致的制造过程中，一定程度的粗糙度和不平整度也是不可避免的。我们表明，相位步进的OD衍射图案特性取决于相位步进表面的粗糙度水平。我们将可检测条纹的数量和衍射图案的自相关函数定义为评估粗糙相位步进衍射与理想情况相似性的指标。我们推导出理论描述，并通过模拟和实验对结果进行了验证。
