Idicula Moncy Sajeev, Kozacki Tomasz, Józwik Michal, Mitura Patryk, Martinez-Carranza Juan, Choo Hyon-Gon
Faculty of Mechatronics, Warsaw University of Technology, 8 Sw. A. Boboli Street, 02-525 Warsaw, Poland.
Media Research Department, Electronics and Telecommunications Research Institute, 218 Gajeong-ro, Yuseong-gu, Daejeon 34129, Korea.
Sensors (Basel). 2021 Dec 29;22(1):214. doi: 10.3390/s22010214.
Surface reconstruction for micro-samples with large discontinuities using digital holography is a challenge. To overcome this problem, multi-incidence digital holographic profilometry (MIDHP) has been proposed. MIDHP relies on the numerical generation of the longitudinal scanning function (LSF) for reconstructing the topography of the sample with large depth and high axial resolution. Nevertheless, the method is unable to reconstruct surfaces with large gradients due to the need of: (i) high precision focusing that manual adjustment cannot fulfill and (ii) preserving the functionality of the LSF that requires capturing and processing many digital holograms. In this work, we propose a novel MIDHP method to solve these limitations. First, an autofocusing algorithm based on the comparison of shapes obtained by the LSF and the thin tilted element approximation is proposed. It is proven that this autofocusing algorithm is capable to deliver in-focus plane localization with submicron resolution. Second, we propose that wavefield summation for the generation of the LSF is carried out in Fourier space. It is shown that this scheme enables a significant reduction of arithmetic operations and can minimize the number of Fourier transforms needed. Hence, a fast generation of the LSF is possible without compromising its accuracy. The functionality of MIDHP for measuring surfaces with large gradients is supported by numerical and experimental results.
利用数字全息术对具有大间断的微样本进行表面重建是一项挑战。为克服这一问题，人们提出了多入射角数字全息轮廓术（MIDHP）。MIDHP依靠纵向扫描函数（LSF）的数值生成来重建具有大深度和高轴向分辨率的样本形貌。然而，由于需要：（i）手动调整无法实现的高精度聚焦，以及（ii）保留LSF的功能（这需要捕获和处理许多数字全息图），该方法无法重建具有大梯度的表面。在这项工作中，我们提出了一种新颖的MIDHP方法来解决这些限制。首先，提出了一种基于LSF获得的形状与薄倾斜元件近似形状比较的自动聚焦算法。事实证明，这种自动聚焦算法能够以亚微米分辨率实现焦平面定位。其次，我们提出在傅里叶空间中进行用于生成LSF的波场求和。结果表明，该方案能够显著减少算术运算，并能最小化所需的傅里叶变换次数。因此，可以在不影响其精度的情况下快速生成LSF。数值和实验结果支持了MIDHP测量具有大梯度表面的功能。
