Advanced Zinc Germanium Phosphide for Mid-IR Lasers

The Phase II Proposal will address walk-off correction of non-linear crystals. The expected result from the proposed work is a defined strategy for the production of critically or non-critically phase matched walk-off corrected assemblies of uniaxial and biaxial crystals that allows their fabrication and use in efficient frequency converting laser systems. The principal focus of the proposed work will be on uniaxial nonlinear optical crystals for mid-IR high power laser sources. Laser damage on the surface and in the bulk is at least in part due to the use of inefficient, not walk-off corrected nonlinear optical crystals resulting in thermal effects and the need to use a high pump power for a desired output power. Zinc germanium phosphide (ZnGeP2; ZGP) appears to be the most important representative of this group but the chalcogenide AgGaSe2 will also be investigated. In addition, KTiOPO4 (KTP) will receive attention because its use as optical parametric oscillator up to 4 µm IR generation also is principally limited by birefringent walk-off, and for its overall commercial potential. KTP has the additional advantage that it is readily available at comparatively low cost, and can serve as model NLO WOC assembly that is transparent in the visible.