Showing papers by "V.P. Kandidov published in 2003"

Self-transformation of a powerful femtosecond laser pulse into a white-light laser pulse in bulk optical media (or supercontinuum generation)

Abstract: We present experimental and theoretical results on white-light generation in the filamentation of a high-power femtosecond laser pulse in water and atmospheric air. We have shown that the high spatio-temporal localization of the light field in the filament, which enables the supercontinuum generation, is sustained due to the dynamic transformation of the light field on the whole transverse scale of the beam, including its edges. We found that the sources of the supercontinuum blue wing are in the rings, surrounding the filament, as well as at the back of the pulse, where shock-wave formation enhanced by self-steepening takes place. We report on the first observation and demonstration of the interference of the supercontinuum spectral components arising in the course of multiple filamentation in a terawatt laser pulse. We demonstrate that the conversion efficiency of an initially narrow laser pulse spectrum into the supercontinuum depends on the length of the filament with high intensity gradients and can be increased by introducing an initial chirp.

Femtosecond laser pulse filamentation versus optical breakdown in H2O

Abstract: The competition between femtosecond laser pulse induced optical breakdown and femtosecond laser pulse filamentation in condensed matter is studied both experimentally and numerically using water as an example. The coexistence of filamentation and breakdown is observed under tight focusing conditions. The development of the filamentation process from the creation of a single filament to the formation of many filaments at higher pulse energy is characterized systematically. In addition, strong deflection and modulation of the supercontinuum is observed. They manifest themselves at the beginning of the filamentation process, near the highly disordered plasma created by optical breakdown at the geometrical focus.

Nonlinear-optical transformation of a high-power femtosecond laser pulse in air

Abstract: A change in the spectrum and the energy distribution of the light field of a high-power femtosecond laser pulse is studied numerically in a broad range of its spatial scales. It is shown that the effect of filamentation, the generation of a supercontinuum and conical emission, the formation of a ring structure in the distribution of the pulse energy and other effects observed during the propagation of the laser pulse in air are caused by the nonlinear-optical transformation of the light field in the region with dimensions exceeding substantially the transverse size of the filament. The pulse filamentation is accompanied by the redistribution of power in its cross section. The spatio — temporal characteristics of emission calculated for femtosecond laser systems are in quantitative agreement with the experimental data.

Initial phase modulation of a high-power femtosecond laser pulse as a tool for controlling its filamentation and generation of a supercontinuum in air

Abstract: The possibility of controlling the processes of filamentation and generation of a supercontinuum during propagation of a high-power femtosecond laser pulse in air is investigated. Using a numerical simulation, it is shown that the initial phase modulation of the pulse results in a shift of the beginning of the filament from the output aperture of the laser system and in a significant increase in the filament length. The efficiency of the generation of the short-wavelength part of the supercontinuum in a pulse with a negative phase modulation is more than two orders of magnitude higher than for a pulse with a limited spectrum.

Phase filtering of the inphase mode of a linear laser array in the Talbot resonator

Abstract: A technique for phase filtering of the inphase collective mode of a laser array in the Talbot resonator is developed. This technique is based on the formation of the phase distribution of the inphase mode field of the linear array with the finite number of channels close to that of the field of the infinite periodic structure. A simple scheme of the phase corrector, providing the increase in the selectivity of the inphase mode of the laser array in the Talbot resonator, is proposed. It is shown that the width of the principal maximum of the far-field intensity does not increase during the phase filtering.

Conversion of high-power femtosecond laser pulse to supercontinuum in atmospheric air

Abstract: We present the simulations and experimental results on white light generation in the filamentation of high-power femtosecond laser pulse in atmospheric air. We have shown that the strong spatio-temporal localization of the light field in the filament, which provides supercontinuum generation, is sustained due to the dynamic transformation of the field on the whole transverse scale of the beam, including its periphery. Because of the correct consideration of the low-intensity large-scale background of the radiation and high-intensity small-scale filament we obtained the quantitative agreement between the simulated and experimentally obtained conical emission angles of a 250 fs 800 nm 10 mJ pulse. It has been found that the sources of the supercontinuum blue wing are in the rings surrounding the filament as well as at the back of the pulse, where the shock wave formation enhanced by self-steepening takes place. We demonstrated that the conversion efficiency of initially narrow laser pulse spectrum into the supercontinuum depends on the length of filament with high intensity gradients and can be increased by introducing initial chirp into the pulse.

Conversion of high-power femtosecond laser pulse to supercontinuum in atmospheric air

Abstract: We present the simulations and experimental results on white light generation in the filamentation of high-power femtosecond laser pulse in atmospheric air. We have shown that the strong spatio-temporal localization of the light field in the filament, which provides supercontinuum generation, is sustained due to the dynamic transformation of the field on the whole transverse scale of the beam, including its periphery. Because of the correct consideration of the low-intensity large-scale background of the radiation and high-intensity small-scale filament we obtained the quantitative agreement between the simulated and experimentally obtained conical emission angles of a 250 fs 800 nm 10 mJ pulse. It has been found that the sources of the supercontinuum blue wing are in the rings surrounding the filament as well as at the back of the pulse, where the shock wave formation enhanced by self-steepening takes place. We demonstrated that the conversion efficiency of initially narrow laser pulse spectrum into the supercontinuum depends on the length of filament with high intensity gradients and can be increased by introducing initial chirp into the pulse.