Quantitative phase microscopy with a closed-loop feedback control is described. The system is based on a Mach-Zehnder interferometer using a phase-locking technique and measures the change in optical path length while the sample is scanned across the optical axis. The important feature of this system is no need for any unwrapping process, which allows us to measure the sample with highly precise around 2π radian. The spatial resolution is estimated to be less than 1μm, which is limited by the Rayleigh criterion and the sample thickness. The path length resolution is estimated to be less than 1nm, which corresponds to the change in refractive index less than 10^-3 for the sample of 10μm thick. Precise measurements of quantitative phase images by a volume phase holographic grating or a multi-level zone plate array validate the principle and show the accuracy of the methods. The samples depending on wavelength with the pigment such as red blood cell and diatom cells are measured by different wavelength. We quantify its accuracy by measuring calibrated test samples. The technique is applicable to examination of limitation of passage culture, biological cell imaging for diagnosis.

Date Published: 22 September 2011
PDF: 7 pages
Proc. SPIE 8134, Optics and Photonics for Information Processing V, 81340G (22 September 2011); doi: 10.1117/12.893503

Published in SPIE Proceedings Vol. 8134:
Optics and Photonics for Information Processing V
Khan M. Iftekharuddin; Abdul Ahad Sami Awwal, Editor(s)