Optimum phase shift for quantitative phase microscopy in volume measurement

Abstract

Volume measurement of a phase object is one of the most distinctive capabilities of quantitative phase microscopy (QPM). However, the accuracy of a measured volume is limited by the different noises of a measurement system and the finite bandpass filter used in the phase extraction algorithm. In this paper, we analyze the inherent errors in volume measurement with QPM and propose the optimum condition that can minimize these errors. We find that phase information of a sample in the frequency domain nonlinearly oscillates as a function of the phase shift corresponding to the sample and its medium, and that the phase information of a sample inside the bandpass filter can be maximized by a proper phase shift. Through numerical simulations and actual experiments, we demonstrate that the error in phase volume measurement can be effectively reduced by the enhancement of the phase signal inside the bandpass region using an optimum amount of phase, which can be controlled by changing either the medium index or the wavelength of illumination.

A Smart Algorithm for Optimizing Bandpass Filter in Phase Volume Measurement with Off-axis Quantitative Phase Imaging

“…The Fourier transform of Eq. (1) contains three peaks: a DC term corresponding to the ampiltude of the electric fields and two peaks related to phase of sample [13].…”

“…The sample information at high frequencies are dominated by the noises of system. Thus, utilizing a proper bandpass filter is recommended to minimize the effect of the noise far from the peak by [13]:…”

“…During the recent years, the different types of the method have been proposed such as Fourier phase microscopy [1], Hilbert phase microscopy [2], diffraction phase microscopy [3,4], and digital holographic microscopy [5]. Despite the several advantages of the methods such as fast acquisition rate, great temporal stability, and high spatial phase sensitivity [6][7][8], they suffer from the various sources of errors which lead to a decrease in measurement accuracy like out-of-focusing [9,10], speckles and shot noises [11,12], and point spread function of system [13]. The present study seeks to analyze the effect of the length and type of bandpass filter on the phase extraction algorithm.…”

Large step-phase measurement by a reduced-phase triple-illumination interferometer

“…Quantitative phase imaging (QPI) is of fundamental significance for industrial applications as a high-accuracy, noncontact, label-free, 3D imaging technique [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. There are numerous phase retrieval techniques for various industrial applications; however, 2π-ambiguity is a common problem in all of the QPI methods.…”