On the possibility of the amplification of subterahertz electromagnetic radiation in a plasma channel created by a high-intensity ultrashort laser pulse

Longitudinal electron waves in plasma formed at multi‐photon ionization of atoms by a short laser pulse

“…In particular, there is a new possibility of amplification of low-frequency radiation in such plasma. [16] In this communication, it is demonstrated that qualitatively new properties of high-frequency waves arise in plasma formed as a result of atom multi-photon ionization. When photoelectron distribution is mainly represented by electrons appearing at the three-photon ionization of xenon atoms, it is shown that potential high-frequency waves with frequencies greater than the electron plasma frequency exist in photoionized plasma.…”

“…For multi-photon ionization of atoms a photoelectron distribution can be approximated by the isotropic distribution function. [16] At the same time, the distribution of photoelectrons over energy arising at multi-photon ionization is strongly non-equilibrium, which also leads to the appearance of unusual properties of the formed plasma. In particular, there is a new possibility of amplification of low-frequency radiation in such plasma.…”

“…atom ionization is three-photon. [16] The energy of the first peak corresponds to the energy 0 = 3ℏΩ − I i ≈ 2.87 eV, where I i = 12.13 eV is the ionization potential of xenon atoms. Peaks of supra-threshold ionization corresponding to the higher energies are almost absent.…”

“…approximates the probability density to detect photoelectrons with the energy , where 0 is the first peak energy in photoelectron spectrum, Δ is the width of peak, and 0 ≫ Δ . [16] For further calculations using (1), let us introduce the photoelectron velocity distribution function…”

“…The relaxation time is the value of the order of the inverse frequency of electron-electron collisions or the inverse frequency of inelastic collisions with neutral xenon atoms. At atmospheric pressure, for the considered xenon plasma with a photoelectrons density of 2.5 ⋅ 10 15 cm −3 corresponding to the ionization degree ∼10 −4 , the relaxation of initial photoelectron distribution (2) is connected with their twin collisions [16] and occurs on time ∼10 −10 s. Below we are interested in the high-frequency longitudinal electron waves in such plasma. The period of these waves is compared with the value 2 / L , where L = √ 4 e 2 n∕m is the Langmuir electron frequency, and e is the electron charge.…”