Double Diffraction of Phase Gratings in the Fresnel Region

Abstract

Double diffraction of phase gratings in the Fresnel region is studied following the previous paper in which double diffraction of amplitude gratings was reported. For sinusodially modulated gratings, series expansion analysis of the contrast in the periodic change in transmitted light intensity as a function of relative displacement was made and the contrast is shown to reach nearly unity for appropriate amplitude of phase modulation. Experimental results on photoresist gratings are found to coincide qualitatively well with theoretical predictions. For double diffraction of two ultrasonic light modulators the characteristics are shown to depend not only on the modulation depth of ultrasonic wave but also on the widths of ultrasonic columns and the angle of incidence.