Biaxial crystals offer a huge advantage for design of acousto-optic tunable filters (AOTFs) because of a variety of two-dimensional transfer functions. Special configurations of noncritical phase matching of anisotropic Bragg diffraction offer the transfer functions suitable for tunable spatial filtering of laser beams, which can be used for phase imaging and laser beam shaping. We analyze special configurations of AOTFs in alpha-iodic acid (orthorhombic system) and potassium yttrium tungstate (monoclinic system) crystals and demonstrate unique two-dimensional transfer functions, which originate from symmetries of the biaxial crystals' refractive index surface. The results include transfer function simulations and corresponding configuration analysis for AOTF design.
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.
Acousto-optic tunable filters (AOTF) enable high-performance imaging spectral photometry used in astronomy, remote sensing, biomedical imaging, and security. An essential feature of AOTFs is polarimetric capability owing to birefringence of crystals used in their design. A spectral polarimeter captures two orthogonal polarizations simultaneously. However, AOTF’s two-dimensional transfer function in polarimetric mode is asymmetric. We demonstrate using chirped driving RF signals to obtain uniform transfer function for two orthogonally polarized Bragg images. This technique can be also used for adjusting the spectral transmission of an AOTF supporting up to 10-fold extension of the passband.
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.
This paper describes the development, manufacturing and testing of acoustooptic (AO) modulator made of bismuth sodium molybdate NaBi(MoO4)2 crystal. Despite the rather long interest in NaBi(MoO4)2 crystals as possible AO material, there is no information about their practical use in acousto-optics. The isotropic orthogonal interaction geometry was used, a longitudinal piezoplate was used as a piezoelectric transducer, the acoustic wave was directed along the crystallographic axis Z. The modulator has shown a high diffraction efficiency (up to 87%) with an RF power of 2.5 W. NaBi(MoO4)2 is characterized by manufacturability during crystal growing and during mechanical processing and optical homogeneity
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.
We report design of acousto-optic imaging spectrometer for spectral and polarimetric photometry and commis- sioning of the instrument at 0.6-m F/12.5 telescope at the Southern Astronomical Station of Lomonosov Moscow State University. The spectrometer was operating over the spectral range 3800–5800 Å with the passband of 10 Å at the wavelength of 5000 Å The imaging spectrometer could be used for observations of objects with the minimum brightness of 12.5 mag (for 0.6-m telescope, 120 s exposition, and SNR∼10). Spatial resolution of the spectrometer was estimated better than 1.2”, and the field of view was ∼250”.
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