Nikolai S. Kazak

Formation of higher-order Bessel light beams in biaxial crystals

A transformation of the order of a Bessel light beam (BLB) from zeroth to first and from first to second when propagating light through a biaxial crystal has been studied theoretically and experimentally. The possibility of the formation of higher-order BLBs by means of this effect is confirmed. The transformation of beam order is observed when propagating circularly polarized light along the optical axis of the crystal under conditions of internal conical refraction. It is shown that a proper choice of the crystal length or conicity angle of the incident beam permits complete transformation of a zero-order Bessel input beam into a first-order Bessel beam.

Bessel-like beams with z-dependent cone angles.

The conventional means of generating Bessel-Gauss beams by axicons in the laboratory results in the distinct disadvantage of an abrupt change in intensity at the boundary of the non-diffracting region. We outline theoretically and then demonstrate experimentally a concept for the creation of Bessel-like beams that have a z-dependent cone angle, thereby allowing for a far greater quasi non-diffracting propagation region.

Properties of parametric frequency conversion with Bessel light beams

Parametric generation of light by pumping with Bessel light beams is investigated. Advantages of such pumping over pumping with Gaussian light beams are revealed. A theory of azimuth-matched nonlinear interaction of Bessel light beams is developed. It is shown that at such an interaction in the parametric generator the coupling coefficient reaches its maximum and no destruction of the spatial structure of intracavity fields at high coefficients of conversion occurs. This opens up the possibility of increasing the energy conversion from an input Bessel beam compared to that of a Gaussian beam. The possibility of high-efficiency parametric conversion of a Bessel pump beam to a Gaussian signal wave beam and a Bessel idler wave beam is shown.

Acoustooptic refraction-influenced generation of tunable incomplete Airy beams

In the process of acoustooptic refraction of an incident-finite- aperture light beam on a standing acoustic wave, there arises a cubic phase modulation of the beam in passing through an acoustooptic cell. After the Fourier transformation of the transmitted field, an Airy-type beam is formed with varying in time parameters. The propagation of such a beam is described explicitly with diffraction integral. By using the numerical simulation, it is established that the transverse intensity profile, acceleration and additional modulation of oscillations of a generated incomplete Airy beam are dependent on the frequency and power of an acoustic wave.

Propagation of high-order circularly polarized Bessel beams and vortex generation in uniaxial crystals

We investigate the generation and transformation of Bessel beams through linear and nonlinear optical crystals. We outline the gen- eration of high-order vortices due to propagation of Bessel beams along the optical axis of uniaxial crystals and expand this to the nonlinear regime by outlining a new phase-matching process (full conical phase matching) in second harmonic generation of vector Bessel beams for various sym- metries in uniaxial crystals. We demonstrate the principles experimentally in a uniaxial BBO crystal and find excellent agreement between the ex- perimental and theoretical results. The results imply a coupling of the intrinsic and extrinsic optical angular momentum of the resulting fields, which may have importance in studies involving quantum entanglement of the angular momentum basis of light. C 2011 Society of Photo-Optical Instru-

Methods of formation and nonlinear conversion of Bessel optical vortices

Linear and nonlinear processes of generation and transformation of optical vortices in crystals were investigated. New universal methods for production of Bessel light beams with optical vortices of the first, second and higher order by means of uniaxial and biaxial crystals were proposed. Light beams with optical vortices of topological charge +/- 1 and +/- 2 are experimentally obtained using KTP and HIO3 (iodic acid) biaxial crystals. We studied type II second harmonic generation by Bessel beams with optical vortices in nonlinear crystals. Results of investigation of the processes of Bessel light vortex order doubling, transfer of vortex to the second harmonic radiation, and annihilation of optical vortices with the opposite signa are presented.

Propagation of ultrasonic beams in paratellurite crystal

Analytical expressions have been obtained of the main curvatures of the concavity of the wave vector surface, corresponding to the quasi-transverse wave, versus anisotropy parameter C = C11-C12-2C66 of the paratellurite crystal. Changes in the form of the sound beam on scanning in the direction of its propagation in the (001) and (110) planes have been investigated. It has been found that near the acoustic axis lying in (001) considerable transformation of the beam takes place; initially extended, it becomes squeezed along the [001] axis. The conditions for focusing and channelling of ultrasound radiation have been determined. The propagation directions at which anisotropy of the paratellurite crystal does not influence the beam divergence have been found. It is shown that, for a wide range of deviation angles theta of the wave normal from the [001] axis in the symmetry plane (110) (theta < or = 50 degrees), the presence of anisotropy leads to weaker diffraction broadening. The character of variation in the direction and divergence of the sound beam on scanning in the vicinity of the [110] direction has been studied experimentally.

Transformation of phase dislocations under acousto-optic interaction of optical and acoustical Bessel beams

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.

Energy flow patterns in an optical field formed by a superposition of evanescent Bessel light beams

A theory of the generation of a superposition of evanescent Bessel light beams (BLBs) at the boundary of two dielectrics is developed, the conditions of total internal reflection being fulfilled. Correct analytical expressions are obtained for the field formed inside a medium having a lower refractive index. The longitudinal and transversal (azimuthal and radial) energy flow densities near the boundary have been calculated and analyzed. Our study demonstrates that it is feasible to use a superposition of evanescent BLBs as a virtual tip for near-field optical microscopy with a sub-wave resolution and for optical tweezing.

Spin-to-orbital angular momentum conversion for Bessel beams propagating along the optical axes of homogeneous uniaxial and biaxial crystals

A study is made of the dynamics of the spin-to-orbital angular momentum conversion for zero-order and high order circularly polarized Bessel beams propagating along the optical axes of homogeneous uniaxial and biaxial crystals. Implementation of Bessel beams and a slab of homogeneous uniaxial crystal allow one to realize a highly efficient (about 100%) optical process in which the direct conversion of the optical angular momentum from the spin form to the orbital form takes place. It is shown that only in a biaxial crystal is there freedom from compensation of spin and orbital angular momentum exchanges with matter and, as a result, the optical torque emerges, which influences the plate.