Self-phase modulation in various regimes of intense laser–plasma interactions

Abstract

Creation of plasmas by intense laser pulses and consequent laser–plasma interactions involve highly non-linear processes. In particular, a variation of the refractive index induced by the laser action turns into a self-phase modulation (SPM) of the laser field. This effect, already observed with nanosecond laser pulses, achieves striking evidence with ultra-short pulses whose intensity can produce index changes in a time as short as a single optical cycle. In this condition, spectral modifications of the laser pulse produced by SPM may strongly modify the laser–plasma interaction. At the same time, the spectral analysis of the transmitted and scattered laser radiation gives valuable information on a variety of processes occurring in the plasma. In this paper we simply consider a few results, which can be attributed to SPM, with the aim of comparing nanosecond and sub-picosecond laser interaction regimes at moderate laser intensities.

Characterization of X-ray radiation from solid Sn target irradiated by femtosecond laser pulses in the presence of air plasma sparks

“…This demonstrates the existence of a parameters region where the laser intensity reaches a maximum value independent from the energy ratio between the prepulse and the main pulse. Previous works demonstrated that blue-shifts of some tens of nanometers can be related to efficient multi-photon ionization, and a constant shift can be related to a fixed laser intensity (Giulietti & Giulietti, 2015 and references therein; Koga et al, 2000). This leads to the conclusion that the role of the prepulse is in modifying the index of refraction of the air plasma, determining a maximum intensity for the main pulse capable to interact with the air-Sn plasma accelerating electrons up to many keV.…”

Self-phase modulation effects as laser produced plasma diagnostics

“…As described in the next section, the local variation of n e on a timescale comparable with the laser wave period T 0 = 2π/ω 0 induces a consequent spectral change of the laser light. Usually such fast µ-variations are directly or indirectly produced by the action of the intense laser light on the medium and the process is then called Self-Phase Modulation (SPM) [1]. Beside laser-plasma interaction, SPM has been studied theoretically and experimentally in a variety of contexts and in some cases it has been used for important applications.…”