SBIR-STTR Award

We propose a laser beam cleanup, the nonspatial filter, which 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 angle. This eliminates the need for laser beam focusing, which is the source of many of the 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. Instead, we propose to fabricate our own material using two commercially available photopolymers. One will be pre-exposed to create a porous but rigid host structure for the other, which will be used to write the actual filter hologram.

Keywords:
Holography, Beam Cleanup, Spatial Filtering

Phase I has been very successful. This novel technique for laser beam cleanup 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 angle. This eliminates the need for laser beam focusing, which is the source of many of the 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. Instead, we propose to fabricate our devices using a porous glass matrix as the substrate. This porous substrate will be filled with a holographic sensitive medium and exposed and processed. The rigidity of this host material prevents differential shrinkage of the filter hologram, allowing sub-milliradian angle Bragg selectivity. The Phase I theoretical and experimental results demonstrated unequivocally that the technology works, and works well. Several other applications have evolved using this very thick rigid holographic structure, such as spectroscopy, laser cavity etalon-like structures, etc.

Keywords:
Holography Beam Cleanup Spatial Filtering