Interference microscopy for biospecimen characterization based on the moiré phenomena is described. Two scenarios of incoherent multiplicative superimposition are employed: (1) object information carrying interferogram is superimposed with reference one or (2) two object interferograms are superimposed (with equal or opposite phase signs). Second strategy provides additional doubling of underlying phase function of interest. Superimposition can be performed using two experimental interferograms or single real interferogram and numerically designed reference structure in so-called digital moiré regime. Multiplicative superimposition of two periodic intensity distribution yields moiré pattern containing low spatial frequency difference beat term (moiré fringes – macrostructure) and high spatial frequency sum beat term (microstructure). The macrostructure was studied in great majority of previously reported moiré techniques. In this contribution we point attention onto the sum beat spatial frequency component and report efficient means for its recovery using numerically advanced digital filtering (variational/empirical decomposition approaches). Its single-frame (single-pattern) phase demodulation by 2D Hilbert spiral transform with enhanced accuracy follows - this feature comes from the fact that sum beat moiré term has high spatial frequency which is generally beneficial in single-frame fringe analysis and its phase function is be doubled. In particular spatial phase change is better sampled by fringes for denser interferogram and more importantly numerical filtering of fringe term of interest from background intensity is easier. We propose and preliminarily evaluate experimental proof-of-concept strategy where two interferograms with slight difference in spatial frequency are simultaneously recorded in two halves of CCD camera and superimposed multiplicatively. Proposed moiré technique opens up new possibilities in interference microscopy based bio-phase imaging mainly due to its data-driven enhanced phase sensitivity (fringe doubling effect) and real-time operation. Evaluation employing numerical simulations and validation using experimental recordings of phase bio-samples, i.e., prostate cancer cells are enclosed.

Date Published: 18 August 2018
PDF: 19 pages
Proc. SPIE 10749, Interferometry XIX, 107490H (18 August 2018); doi: 10.1117/12.2323601

Published in SPIE Proceedings Vol. 10749:
Interferometry XIX
Katherine Creath; Jan Burke; Michael B. North Morris; Angela D. Davies, Editor(s)