Abstract

An array illuminator is proposed using a phase grating in the entrance plane. The grating is illuminated uniformly and converted into the amplitude image with the help of a phase contrast setup. The conversion is brought about by a proper choice of the grating phase structure in combination with a suitable phase shift of the zero-order diffraction in the phase contrast setup. The result is a light distribution of bright areas surrounded by darkness. Since the phase grating is periodic, only one elementary cell of this grating need be considered to get the necessary condition for the phase delays in the grating and phase platelet. The compression ratio p defined as the quotient of the bright area to the cell area is limited to 1 > p ⩾ 1/4 due to the underlying two-beam interference phenomenon. Cancellation in the dark surrounding is total only in this compression range. If the total cancellation in the dark area is given up, arbitrary compression ratios can be attained although the energy concentration is limited to a factor of ~5.

© 1987 Optical Society of America