Characteristic features of generation of few-cycle pulses in infrared and terahertz spectral ranges upon interaction of two femtosecond pulses of different frequencies in air |
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Authors: | S A Stumpf V G Bespalov A A Korolev and S A Kozlov |
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Institution: | 1.St. Petersburg State University of Information Technologies, Mechanics and Optics,St. Petersburg,Russia |
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Abstract: | The results of a theoretical analysis of the generation of broadband radiation in the infrared and terahertz spectral ranges
upon the excitation of plasma in air by two femtosecond pulses at the fundamental and second-harmonic frequencies of a Ti-sapphire
laser are presented. It is found that the appearance of long-wavelength radiation in a strong field of pulses of different
frequencies can be described in terms of strongly anharmonic oscillations of optical electrons, whereby electrons are pulled
far away from their atoms; these oscillations are accompanied by cascade transitions of electrons from their ground state
to a bound excited state, followed by a transition to the continuum. It is shown that the generated infrared and terahertz
radiation appears in the form of pulses containing a few oscillations of the light field. The efficiency of terahertz generation
varies periodically with an increase in the interaction length of the femtosecond pulses of different frequencies. |
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