Optics and Photonics Society of Iran

In this paper, a method based on Fresnel diffraction from a parallel phase plate is presented for the phase study of micron- sized transparent samples. If a transparent plate is located in the path of a monochromatic beam of laser light, the diffraction fringes appear due to an abrupt change in the optical path length (OPL) difference between the part of the incoming light passing through the plate and the other propagating in the air. Now, if another phase sample is located in the path of the incoming light to the plate, the diffraction fringe pattern changes. the phase information of the sample can be extracted within the fringes by different fringe analysis methods. The presented setup is simple in comparison with complex interferometry techniques and the fringe pattern is stable against any mechanical and optical vibrations. Also, the accuracy of phase measurement is comparable with other common methods in which anti-vibration tables and high precision optical elements are required. By using this method, some measurements are performed on Red Blood Cells (RBC) and the results are compared with digital holographic microscopy (DHM) technique. The results indicate the high efficiency of technique in study of microscopic samples and nanometric variations in the membrane of living cells