V. Pyragaite

Free-space propagation of overlapping light vortex beams

The propagation of a combined beam consisting of two noncoaxial vortex beams is investigated. It is demonstrated that the vortical properties of the combined beam under diffraction depend on propagation length as well as on amplitude ratio of individual beams.

Ultrabroad Bandwidth of Optical Parametric Amplifiers

Optical parametric chirped pulse amplifiers (OPCPAs) are widely recognized and rapidly developing devices for high-power femtosecond pulse generation. In this paper we reveal the main issues of OPCPA gain bandwidth extension for amplification of pulses with octave-spanning spectra.

Interference of intersecting singular beams

Abstract A vorticity of the light field created by interference of two intersecting Laguerre–Gaussian singular beams is analysed. It is demonstrated that the number and location of the vortices present in the field depend on the propagation length as well as on the topological charges of the individual beams, their intersection angle and amplitude ratio.

Noncollinear interaction of optical vortices in Kerr nonlinear medium

The noncollinear interaction of singular light beams (degenerate four-wave mixing) in Kerr nonlinear medium is analyzed. It is demonstrated that vorticity of diffracted beams significantly depends on the topological charges of pump beams. The results of an experimental observation of the phenomenon are presented.

Generation of coherent waves by frequency up-conversion and down-conversion of incoherent light

It is revealed that the generation of a coherent wave by frequency conversion of incoherent waves is a characteristic feature of three-wave interaction in a nonlinear medium when angular dispersion of input waves is properly chosen. In this case the combining action of the pairs of spectral components of incoherent waves may result in the cumulative driving of a single plane monochromatic wave in up-conversion and down-conversion processes. As a fundamental result we point out an enhancement of the spectral radiance of the generated wave in comparison with incoherent waves.

Spectrum of second-harmonic radiation generated from incoherent light

We report on the development of the theory of second-harmonic generation by an incoherent pump with broad angular and frequency spectra. We show that spatial as well as temporal walk-off effects in a nonlinear crystal result in angular dispersion of the second-harmonic radiation. We demonstrate that the acceptance angle in second-harmonic generation by incoherent light is caused by the width of the pump angular spectrum and the resulting angular dispersion of second-harmonic radiation but does not depend on crystal length. In this case the frequency spectrum of second-harmonic radiation is determined by its angular dispersion and the pump angular spectrum. The theory is supported by an experiment in which a LiIO{sub 3} crystal was pumped by a tungsten halogen lamp.

Narrowing of angular spectrum of second harmonic beam generated by incoherent conical pump

Second harmonic generation can serve for improvement of coherence in two-dimensional case. Incoherent pump beams should obey conical geometry. Then, the angular spectrum of the generated second harmonic beam narrows during the propagation in nonlinear crystal.

Parametric down-conversion of higher-order Bessel beams in nonlinear crystals

It is revealed that orbital angular momentum can be conserved within the spontaneous parametric down-conversion of higher-order Bessel beam. A qualitative agreement of theoretical predictions with experimental results is obtained.

Parametric down-conversion of Bessel vortex beam in quadratic medium

This study predicts and demonstrates that orbital angular momentum (OAM) is conserved within the spontaneous down-conversion of Bessel vortex beam in optical parametric generators (OPG). Results show that the output radiation of CDA-based OPG pumped by Bessel vortex beam consists of two pairs of OAM-free axial (Gaussian-like) beam and the conical (Bessel-like) beam, the OAM of which is equal to OAM of pump beam. Hence, the OAM is conserved within the spontaneous parametric down-conversion of higher-order Bessel beams in contrary to OPG pumped by Laguerre-Gaussian modes. That is the result of strong transverse selection of spontaneously arising fields in OPG pumped by Bessel beams.