The generation of wavefront phase dislocations of vortex Bessel light beams under acousto-optic (AO) diffraction in uniaxial crystals has been investigated. For the first time the process of AO interaction is studied with participation of Bessel acoustic beams instead of plane waves. A mathematical description of AO interaction is provided, which supposes the satisfaction of two types of phase-matching condition. The acousto-optic processes of transferring optical singularities onto the wavefront of BLBs are investigated and the generation of high-order optical vortices is considered at the interaction of optical and acoustical Bessel beams. The change of Bessel function order or phase dislocation order is explained as a result of the spin–orbital interaction under acousto-optic diffraction of vortex Bessel beams.
535.423The features of the frequency doubling of elliptic Bessel light beams under quasi-synchronous interaction in periodically polarized nonlinear crystals have been investigated. The overlap integrals describing the efficiency of second-harmonic generation by elliptic Bessel light beams have been investigated numerically.Keywords: elliptic Bessel light beam, periodically polarized nonlinear crystals, second harmonic generation. Introduction.In the last few years, periodically polarized nonlinear crystals (PPNC) have been widely used for nonlinear-optical frequency conversion [1,2]. Among the most frequently used PPNCs are crystals of LiNbO 3 , LiTaO 3 , KTP, KNbO 3 , and others, in which all three-frequency interactions traditional for nonlinear optics are realized [3]. One advantage of these crystals is the possibility of using new kinds of interactions (oo → o and ee → e) upgrading the efficiency of second-harmonic generation (SHG) due to the involvement in the nonlinear process of the maximal, in value, components of the nonlinear susceptibility tensor [4][5][6]. At the same time, the interest in the investigation of the nonlinear-optical interaction by Bessel light beams (BLB) is due to the special structure of their spatial spectrum that permits using various vector interactions in the nonlinear processes [7-9].Results and Discussion. This work is devoted to the investigation of the feature of the elliptic BLB frequency doubling under quasi-synchronous ee → e interaction in PPNs. We consider crystals with a perfect periodic structure composed of oppositely polarized domains whose thicknesses are equal to the coherent length and whose effective nonlinear coupling coefficients change sign on going from one region to another.In investigating the propagation, as well as the parametric and nonlinear BLB frequency conversion in anisotropic crystals, the problem of correct description of the polarization of beams corresponding to extraordinary waves (etype BLBs) arises. In particular, under three-frequency conversion of BLBs at least one of them is an e-type beam. From geometrical considerations it is easy to see that for these beams the wave vectors of the spatial frequency spectrum will form not a circular cone, as usual, but an elliptic one. Let us direct the y-axis of the Cartesian coordinate system along the optical axis of the crystal and the z-axis -in the direction of the beam propagation. Thus, the cone axis of the wave vectors of the BLB is oriented perpendicularly to the optical axis. The components of the E-vector of the elliptic BLB in the cylindrical coordinate system (ρ, ϕ, z) have the following form:
The peculiarities have been studied of acoustooptic (AO) diffraction of quasi-nondiffracting vector Bessel light beams (BLB) on the ultrasound waves in optical gyrotropic cubic crystals. The system of coupled equations describing the process of acoustooptic interaction is solved, diffraction efficiency has been calculated. The mathematical description of AO interaction, which differs from the similar description for the plane optical waves means of two types of synchronism, is conducted. It is shown that besides the usual longitudinal synchronism realized at the equality of phase velocities transmitted and diffracted waves, for Bessel beams it is also necessary to perform the so-called transverse synchronism. It is related with the fact, that Bessel beams with differing cone angles have different spatial structure and, consequently, various values of overlap integral with the input beam. The possibility has been investigated of transformation of the order of phase dislocation of Bessel beams wave front due to AO diffraction. It is proposed to use the process of acoustooptic diffraction in gyrotropic cubic crystals as a method for dynamic manipulation of polarization state of output Bessel beam, particularly for transformation of left-to right (and vice versa) polarization states.
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