Versatile approach to laser beam shaping and analyzing by holographic phase masks

Abstract

A new technology that includes a flexible holographic recording system using photo-thermo-refractive (PTR) glass is demonstrated for creating so-called ‘holographic phase masks’ or HPMs. These diffractive optical elements are permanently recorded in the PTR glass, can be multiplexed as with normal holograms, do not require electric power to operate, and can perform near arbitrary beam phase transformations. The holographic setup includes a spatial light modulator that enables recording transmitting volume Bragg gratings (VBGs) with arbitrary phase patterns encoded into them. As a result, the desirable phase pattern is introduced in a beam that is diffracted by the VBG. These HPMs are tunable within the visible and near IR spectral regions and can be made achromatic, with spectral widths of up to 50 nm. Furthermore, they tolerate laser power densities on the order of several kW cm−2. Applications of HPMs include high-power, broadband laser beam shaping and modal analysis of complex beams profiles, both of which are demonstrated here.