A prototype of two-coordinate spatial light modulator (SLM) based on acousto-optic diffraction in KY(WO4)2 monoclinic crystal is proposed. The SLM design is based on a special configuration of isotropic Bragg diffraction in monoclinic crystals, which used autocollimation of the acoustic beams and operation with unpolarized light. This enables a unique design of a two-coordinate Bragg cell, which can be used as a monolithic X-Y deflector or as an SLM. Experimental results and limitations of the prototype performance are discussed in the report. Overall efficiency over 50% at 4 W of driving RF power has been demonstrated for the laser wavelength of 532 nm. Optical modulation rise/fall time is ~220 ns/mm for each coordinate.
We designed a new configuration of acousto-optic spatial light modulator based on biaxial crystal KY(WO4)2 (KYW). This material has proved to be a good candidate to fill the gap between paratellurite having high acousto- optic efficiency and quartz having low efficiency but high laser-induced damage threshold. The modulator uses isotropic diffraction by a slow quasi-shear bulk acoustic wave propagating in the autocollimation direction. This ensures good compromise between acousto-optic figure of merit, which is only 30% less than in z-cut longitudinal- wave paratellurite, and high laser-induced damage threshold. The prototype modulator has the spatial resolution of 250 with the central frequency of 100 MHz and the aperture of 20 mm. The designed spatial light modulator is aimed at high-power ultrashort laser pulse shaping applications in near and middle infrared.
We designed a high-efficient acousto-optic Q-switch based on a potassium yttrium tungstate crystal (KY(WO4)2), or KYW. Isotropic acousto-optic interaction along NmNg plane of dielectric axes of the crystal was used. The Q-switch operated at the wavelength of 2.1 μm of a Ho:YAG laser with the diffraction efficiency over 60% at the RF driving power of 20 W. No laser damage of the crystal with antireflection coatings was observed at 12 J/cm2 fluence for nanosecond pulses.
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