Production refinements and pragmatic optical properties of the frequency converter crystal KNbO3 (KN) are highlighted regarding its commercialization. The growth, morphological orientation, and processing of KN crystals into devices are outlined. Passive absorption data are presented that define the effective window range for KN devices. An absorption band at 2.85 micrometers is attributed to the presence of OH groups in the crystal, and its vibrational strength varies with crystal growth conditions and incident polarized light orientation. Although blue light induced infrared absorption (BLIIRA) can reduce second harmonic generation (SHG) efficiency at high powers, single-pass conversion efficiencies of 1%/W(DOT)cm may be achieved with incident fundamental powers of 10 W. The ability of KN to noncritically phasematch by temperature tuning provides blue-green wavelengths; together with critical angle-tuned phasematching, the entire visible spectrum may be accessed with efficient SHG conversion.
Two key obstacles to the development of high-capacity three-dimensional information mass storage systems using photorefractive crystals are: (1) readout of holograms stored in the conventional manner is destructive, and (2) undoped photorefractive crystals are typically quite insensitive to red and infrared write light from diode lasers (the preferred source). As a consequence, bulky, expensive ion lasers have been necessary for hologram writing. Thus hologram fixing and high infrared sensitivity in these materials are both important if practical systems are to be built. We present our own high-temperature (80-110°C) photorefractive grating writing results for a variety of pure and doped barium titanate (BaTiO3) crystals. We found strong fixable secondary gratings that correlated with increasing levels of Fe and Ni in doped crystals. Fixing was not observed in our pure crystals or those doped with V, Rh, or Co. Fixing was enhanced in an iron-doped crystal reduced by high-temperature annealing at low oxygen partial pressures. We also found that the readout diffraction efficiency of a fixed grating in BaTiO3 is a rapidly increasing function of readout temperature above a threshold temperature, which depends upon the crystal orientation. Lower temperatures lead to longer storage times, as would be expected if the carriers forming the fixed grating have a thermally activated mobility. We also report preliminary experimental results on blue Rh-doped BaTiO3 crystals with fast and high-gain infrared (840 nm) response.
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