A novel device, the nonspatial filter, is described for laser beam cleanup. It is based on the Bragg selectivity of thick holograms. Unlike pinhole and fiber spatial filters, which employ lenses and apertures in the transform plane, nonspatial filters operate directly on the laser beam. This eliminates the need for laser beam focusing, which is the source of many of the material and alignment instabilities and laser power limitations of spatial filters. Standard holographic materials are not suitable for this application because differential shrinkage during processing limits the maximum Bragg angle selectivity attainable, and because they are generally too thin. New technologies that eliminate the problem of differential shrinkage are described. These technologies are based either on the use of a rigid porous substrate material, such as porous glass, filled with a light-sensitive material, such as holographic photopolymers or dichromated gelatin, or on the use of a thick photopolymer with diffusion amplification (PDA). We report results of holographic nonspatial filtering of a laser beam in one dimension, with an angular selectivity of better than 1 mrad.
- Spatial filtering
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics