Holographic filters with adjustable transmittance for high power lasers

"The overall objective of the proposal is to develop the technology of production of robust filters with adjustable transmittance based on the phase Bragg gratings in photo-thermo-refractive (PTR) glass. This glass is a very promising photosensitive mediumfor volume holograms because it has excellent response at any spatial frequencies up to ~10000 mm-1, large spectral window from 300 to 4000 nm, and perfect thermal, optical and mechanical stability. The adjustable filters should enable to vary thetransmitted power of laser beam including high power laser radiation at least 100 times for selected wavelength in the indicated region. Total losses of beam power should not exceed (5-10)%. The important features of these filters will be an attenuationjust of selected wavelength, large working area and homogeneously variable transmittance, high laser-induced damage threshold, and a stability of parameters over a long period of work. Such holographic mirrors can be the key components for differentoptical systems developed for task BMDO/02-001 which utilize laser beams including high power radiation. The target is the adjustable filters in photosensitive silicate glass. They are absent now on the market, though the stability of filters in silicateglasses is higher than normal filters and they can be favorable priced. Moreover, they are very promising for using in large-aperture high power laser systems because they have relatively small