Amplification of terahertz radiation in inhomogeneous plasma produced by multiphoton ionization of inert gas in a magnetic field

The reflection and transmission coefficients of an electromagnetic wave interacting with an inhomogeneous plasma layer produced by multiphoton ionization of an inert gas in a magnetic field are determined. The possibility of terahertz radiation amplification is revealed. If the frequency of the probe radiation matches the electron cyclotron frequency, the field strength of the transmitted and reflected radiation can be amplified by more than two orders of magnitude. The amplification arises due to the Ramsauer-Townsend effect and the non-equilibrium energy distribution of the photoelectrons. Blurring the plasma boundary by an amount equal to a few percent of the uniform layer width results in a small decrease in radiation amplification. The energy spread of photoelectrons reduces the amplification by several times.