Measurement of large discontinuities using single white light interferogram

Abstract

White light interferometry is a widely used tool to extend the unambiguous measurement range of a monochromatic interferometer. In this work, we discuss Hilbert transformation analysis of a single white light interferogram acquired with a single-chip color CCD camera for step height measurement which lies beyond the unambiguous range of the monochromatic interferometry. The color interferogram is decomposed and phase maps for red, green, and blue components are calculated independently using Hilbert transformation. This procedure makes the measurement faster, simpler, and cost-effective. The usefulness of the technique is demonstrated on micro-sample.

Multi-colour microscopic interferometry for optical metrology and imaging applications

“…To implement FOM, phases measured at three different wavelengths are required. The phase is governed by the following equation [16,30,53,74] (…”

“…Single-shot measurements where only a single frame or multiple frames in one go are recorded and analyzed for phase by an appropriate procedure have been reported. In recent years, numerous single-frame analysis methods such as Fast Fourier Transform (FFT) [25][26][27], Huang-Hilbert transformation (HHT) [26,28], Hilbert Transform (HT) [29][30][31], Pixelatedpolarization phase shifting (PPPS) [20,32]etc. have been applied for single-interferogram analysis.…”

“…The Bayer filter 1-CCD RGB camera has been demonstrated for surface profiling of large discontinuities [23,51,58,59], and simultaneous measurement of shape and deformation [23,48], non-destructive testing (NDT) of large defects [60], simultaneous acquisition of blood flow, blood volume, and oxygenation on human fingers using dualwavelength laser imaging [61]etc. Recently, white light illumination combined with 1-CCD RGB camera was successfully demonstrated for surface profiling of micro-lens array and large-discontinuities [30], biological cells such as human Red-Blood-Cell (RBCs) [21,50,62], onion skin/cells [22], fish-eye cornea [55]etc. This approach was further simplified by using single-shot methods instead of multiple-frame methods for phase measurements [21,23,24].…”

Phase retrieval algorithm for line-scan dispersive interferometry

“…The height obtained by phase slope method is close to the actual value and it can be further improved. This value is used to estimate the fringe order ℱ N of the spectrally resolved interference signal, which is described by formula [13]…”

Snapshot multi-wavelength interference microscope

“…One of the limitations is that the phase difference between two adjacent points must be less than , limiting the measurement range. To overcome this limitation, vertical scanning is typically used [1][2][3][4][5]. Multi-wavelength interference microscope is the other approach [6][7][8].…”