N A Khilo

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.

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.

Shape invariant higher-order Bessel-like beams carrying orbital angular momentum

We present a method for generating higher-order Bessel beams with z-dependent cone angles. Such fields, if engineered correctly, are shape invariant during propagation and thus do not suffer from a transition from a Bessel-shaped intensity profile in the near field to an annular ring in the far field. We demonstrate the production of such fields in the laboratory with an optical system comprising a combination of two axicons and a lens, allowing for control of the cone angle of the resulting field. While the resulting shape invariant fields are not perfectly non-diffracting, they do maintain many of the same properties as Bessel beams, including self-reconstruction.

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.

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.

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.

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.

Modal theory and output patterns of Stokes radiation in SRS: generation at pump with Bessel light beams

A new theoretical model of SRS for a Bessel pump beam is presented. The experimentally observed regularities of SRS, concerning the formation of output patterns an nearly diffraction-limited axial Stokes beam are explained within the framework of this model. The model represents the Stokes radiation as a superposition of partial Bessel modes if a cylindrical waveguide is formed by a pump beam.

Methods of formation of gradient light fields

The practical methods of formation of multi-ring and multi- beam gradient light fields are proposed and experimentally realized. These methods are based on the use of crystals, refracting elements with different configurations, and special optical resonators. The obtained gradient light fields have geometrically regular spatial intensity distributions and different types of symmetry. The process of second harmonic generation with gradient light fields was investigated. Gradient light fields and their second harmonic have promising perspectives both for optical information processing and for some technologies, such as cool particles control in nanotechnologies, operations with organic cell and its components, local radiation material processing, and production of some periodic structures.

Second harmonic generation by a quadribeam

The scheme for obtaining quadri-beams is studied theoretically and experimentally. In this scheme the quadri- beam is obtained from the plane wave or Gaussian beams using two biprisms. Using optical elements with different number of reflecting planes one can obtain the beams with complex symmetric intensity patterns. The second harmonic generation by quadri-beams is experimentally investigated. The theoretical explanation of the obtained spatial distribution of second harmonic radiation is given.