Electron Beam Processing of ZnGeP2: A Nonlinear Optical Material for the Infrared

Zinc germanium phosphide, an important frequency-conversion material for producing mid-infrared lasers, is plaqued by a detect-related absorption band extending from the fundamental edge (0.62 microns) to ∼3 microns. The level of absorption varies with melt composition, and can be reduced by post-growth annealing treatments. In these experiments, further reduction of the near-band-edge absorption was achieved by irradiating with 1-1.5 MeV electrons at cumulative fluence levels up to 2.75xlOI8cm2. Ge-rich, ZnP2-rich, and both as-grown and annealed stoichiometric crystals were studied. The near-edge absorption of the higher-loss, nonstoichiometric samples decreased monotonically with each subsequent irradiation, whereas the absorption in the lower-loss, stoichiometric samples was minimized after cumulative electron fluences of 2 x 10I8cnv2 and 1 x 10I8cm2 for as-grown and annealed material respectively. The minimum absorption coefficient achieved at 1/im was ∼4.4cnr’ in both stoichiometric samples, representing a factor two decrease for the as-grown crystal. Further exposure after reaching saturation served only to increase the losses at longer wavelengths.