Resonant four-photon scattering of collinear laser pulses in plasma

TL;DR

This paper demonstrates that relativistic electron nonlinearities enable resonant four-photon scattering in plasma, leading to significant frequency shifts and potential for tunable high-power lasers in inhomogeneous plasma environments.

Contribution

It reveals that relativistic effects remove classical restrictions on four-photon resonance in plasma, allowing large frequency shifts and broader operational conditions.

Findings

Frequency shifts increase with laser intensity.

Shifts can nearly double the input laser frequency.

Lasers can operate in highly inhomogeneous plasma environments.

Abstract

Exact four-photon resonance of collinear planar laser pulses is known to be prohibited by the classical dispersion law of electromagnetic waves in plasma. We show here that the renormalization produced by an arbitrarily small relativistic electron nonlinearity removes this prohibition. The laser frequency shifts in collinear resonant four-photon scattering increase with laser intensities. For laser pulses of frequencies much greater than the electron plasma frequency, the shifts can also be much greater than the plasma frequency and even nearly double the input laser frequency at still small relativistic electron nonlinearities. This may enable broad range tunable lasers of very high frequencies and powers. Since the four-photon scattering does not rely on the Langmuir wave, which is very sensitive to plasma homogeneity, such lasers would also be able to operate at much larger plasma inhomogeneities than lasers based on stimulated Raman scattering in plasma.