Showing papers by "V.P. Kandidov published in 2022"

Femtosecond multiple filamentation of an optical vortex in the mid-IR wavelength range in fused silica and fluorides

Abstract: The results of experimental and theoretical study of the self-action of femtosecond optical vortices in the region of anomalous group velocity dispersion in fused silica and fluorides are presented. Multiple filamentation of an axially asymmetric annular beam with a phase dislocation of topological charge m = 1 at a wavelength of 1800 nm in a LiF crystal is investigated. It is found that for the experimentally recorded intensity profile of a vortex beam with two maxima on the diameter, the critical self-focusing power is approximately two times larger than the critical power of a unimodal Gaussian beam. In pulses with supercritical power in the vicinity of the intensity maxima, two coupled filaments, separated by a phase dislocation, are formed on the annular profile of the optical vortex, which prevents energy exchange during their formation. The length of vortex-beam plasma channels in a single pulse is found to be about 300 μm at a diameter of about 2 μm, which is close to the characteristics of plasma channels in a Gaussian beam.

Carrier-envelope phase effect on light bullet dynamics

Abstract: A light bullet (LB) is a wave packet of a few optical cycles that is extremely compressed in space and time, which is formed in the bulk transparent dielectric during femtosecond filamentation under anomalous group velocity dispersion. We demonstrate for the first time that the carrier-envelope phase shift during propagation of a near single-cycle LB causes synchronous oscillations of the spatial, temporal and energy parameters of its core with the period decreasing with increasing carrier wavelength. When analyzing the structure of color centers and induced plasma channels in fluorides, it was experimentally found that LB parameter oscillations lead to a periodic change in the nonlinear optical interaction with the dielectric.

Spectral probing of an extremely compressed femtosecond wave packet in calcium fluoride

Abstract: We use time-resolved spectral probing to study the dynamics of transformation of the optical properties of a nonlinear medium during formation and propagation of an extremely compressed mid-IR femtosecond wave packet in calcium fluoride. Broadening, attenuation and distortion of the probe pulse spectrum have been experimentally observed varying the delay time of the probe pulse relative to the pump. By solving the unidirectional pulse propagation equation that describes propagation and filamentation of a pump pulse in a calcium fluoride crystal we determine temporal changes of the refractive index and absorption coefficient induced by an extremely compressed wave packet. A mechanism of the observed broadening and breakup of the probe pulse spectrum is proposed.

Carrier-envelope phase of an elliptically polarized mid-IR light bullet

Abstract: For the first time, the formation of a mid-IR single-cycle light bullet during propagation of a femtosecond laser pulse with an arbitrary initial polarization ellipticity of the light field has been experimentally and numerically investigated. It is established that the polarization ellipticity determines the effect of the carrier-envelope phase on the nonlinear-optical interaction of the light bullet with the medium.

Formation and Dynamics of an Extremely Compressed Mid-Infrared Wave Packet

Abstract: A theoretical and experimental study of the formation and dynamics of a single-cycle mid-infrared wave packet during filamentation under anomalous group velocity dispersion condition is carried out.