A. A. Ushakov

Optimal polarization of a two-colored pump for terahertz generation with a phase-unstable scheme

The polarization properties of a scheme for terahertz (THz) generation by an optical breakdown of a gaseous media using a two-colored femtosecond pulse are investigated. It is found that if the scheme is not stabilized over the phase shift between the pump waves, the maximal THz signal is observed when the pump pulses are elliptically polarized. At this rate the stability of the THz signal power is also maximal. These observations are in compliance with a photocurrent model of THz generation.

Backward Terahertz Radiation from a Two-Color Femtosecond Laser Filament

We report the first experimental observation of backward terahertz emission from the two-color laser induced plasma filament in air. The ratio of measured forward-to-backward terahertz radiation is ∼25/1. This result agrees with numerical simulations based on interferometric model assuming 0.3 mm long plasma source.

Optimization of the laser plasma source of terahertz radiation and interferometric study of its spatio-temporal field distribution

The efficiency of terahertz radiation generation induced by focusing two-color femtosecond laser pulses in the air with different polarization state of the pump fields was studied. A new measurement technique for the detection of the spatio-temporal THz electric field strength distribution in an electro-optic crystal using optical interferometry was demonstrated.

Features of the electron density dynamics in the filamentation of femtosecond laser radiation in air at elevated pressure

The electron density in the plasma channel of a femtosecond filament in air at pressures from 1 to 7 atm is measured at different instants, starting from the ionisation onset and up to several hundreds of picoseconds after it. The initial electron density is found to increase sharply in the pressure range of 3 – 4 atm. The plasma channel diameter is found to decrease with an increase in pressure from 3 to 7 atm.

Generation of terahertz radiation due to air breakdown induced by two-frequency laser pulses with different polarization states

Generation of terahertz radiation during the focusing of dual-frequency femtosecond laser pulses with different polarization states in air is investigated. The dependence of the average power on the degree of ellipticity of the fundamental harmonic is obtained. Calculations based on the nonstationary photocurrent model are performed.

Dependence of the efficiency of terahertz radiation generation on the state of two-color pump field polarization during optical breakdown of air

Terahertz generation when focusing two-frequency femtosecond laser pulses with various polarization states in air at atmospheric pressure is studied. The density of the photocurrent appearing during tunnel ionization under identical conditions is also calculated. The calculated and experimental data are in good agreement.