Fabrication of large-aperture random phase plate for uniform illumination on laser fusion target

Abstract

We have fabricated a large aperture random phase plate (RPP) in Chinese K9 glass substrate for target-plane laser beam smoothing at 1.06 micrometer wavelength, by using large aperture photolithography and dilute HF etching processes. The RPP's clear aperture is (phi) 250 mm. The measured average step height is 1.060 micrometer, which has a relative standard deviation of 1.24% at 5 locations on the RPP to the theoretical value. A focal spot with very sharp edges and nearly flat-top overall envelope intensity distribution is obtained at the focal-plane of a focusing lens. These results show that our fabrication techniques for RPP is effective, and is easily scaleable to even larger apertures.