Nonlinear optical crystal development for laser wavelength shifting at AFRL Materials Directorate

Our objective is to develop crystals that shift the light from well developed laser sources to application specific wavelengths which may be tunable. Military applications extend across the entire spectrum from ultraviolet through the far-infrared but our greatest interest has been in materials for the mid-IR (3-5 mu m) and far-IR (8-12 mu m) atmospheric windows. Our primary applications that drive crystal development are infrared countermeasures and remote sensing of chemical and biological warfare agents. To achieve these results we have pursued two tracks: birefringent bulk materials and quasi-phase-matched structures. Birefringent studies include the grey track problem in KTiOPO4 (KTP) plus growth of its isomorphs, KTiOAsO4 (KTA), RbTiOAsO4(RTA), CsTiOAsO4(CTA) and KxRbl-xTiOPO4 (KRTA); chalcopyrites: ZnGeP2, CdGeAs2, AgGaS2, AgGaSe2, AgGa(1-x)InxSe2, AgGaTe2; plus GaSe, and HgGa2S4. A small portion of the effort is pursuing UV materials, the foremost being the berates MM'(B3O5)(3) where M = Sr, Ba, Pb; M'= Li,Na. Previously, work was done on LiB3O5 (LBO), beta-BaB2O4 (BBO) and CsLiB6O10 (CLBO). Quasi-phase-matched (QPM) techniques include inverted segments by diffusion bonding (GaAs), by periodic poling (LiNbO3, LiTaO3, KTP, BaTiO3) and by periodic doping. To cover the 4.5-5.0 mu m band, work is being done on RTA and Pb{MgxNbyTi1-x-y}O-3 (PMNT). For periodic poling in the 8-12 mu m region studies are being made on CGC (CsGeCl3), CGB (CsGeBr3), Tl3PbBr5, Tl(4)Pbl(6) and Tl4HgI6. QPM can also be obtained using total internal reflection devices (GaAs, ZnSe).