Generation of flat-top beam with phase-only liquid crystal spatial light modulators

A system containing two-phase-only liquid crystal spatial light modulators (LC-SLMs) is designed to convert a quasi-Gaussian beam into a flat-top beam. The first LC-SLM redistributes the intensity and the second LC-SLM re-collimates the reshaped beam. The phase distributions of the LC-SLMs are derived based on energy conservation and the constant optical path length principle. The influences of deviations of the beam waist and beam shape from the assumed value are analyzed in detail. Experimental results show that approximately 71.5% of the incident power is enclosed in a region with less than 6% rms power variation. The performance is compared quantitatively with the theoretical design. The far-field intensity distribution and the phase distribution of the reshaped beam show that the wavefront after reshaping is maintained.