Abstract
Stimulated Raman scattering (SRS) in plasma in a non-eigenmode regime is studied theoretically and numerically. Different from normal SRS with the eigen electrostatic mode excited, the non-eigenmode SRS is developed at plasma density $n_{e}>0.25n_{c}$ when the laser amplitude is larger than a certain threshold. To satisfy the phase-matching conditions of frequency and wavenumber, the excited electrostatic mode has a constant frequency around half of the incident light frequency $\unicode[STIX]{x1D714}_{0}/2$ , which is no longer the eigenmode of electron plasma wave $\unicode[STIX]{x1D714}_{pe}$ . Both the scattered light and the electrostatic wave are trapped in plasma with their group velocities being zero. Super-hot electrons are produced by the non-eigen electrostatic wave. Our theoretical model is validated by particle-in-cell simulations. The SRS driven in this non-eigenmode regime is an important laser energy loss mechanism in the laser plasma interactions as long as the laser intensity is higher than $10^{15}~\text{W}/\text{cm}^{2}$ .
Highlights
Laser plasma interactions (LPIs) are widely associated with many applications such as inertial confinement fusion (ICF)[1,2,3], radiation sources[4], plasma optics[5, 6] and laboratory astrophysics[7, 8]
The transmission rate of the pump laser through plasma is about 19.46% at t = 2000τ, which indicates that non-eigenmode stimulated Raman scattering (SRS) is an important pump energy loss mechanism in the LPI as long as the laser intensity is higher than 1015 W/cm2
We have shown theoretically and numerically that the non-eigenmode SRS develops at plasma density ne > 0.25nc when the laser amplitude is larger than a certain threshold
Summary
Laser plasma interactions (LPIs) are widely associated with many applications such as inertial confinement fusion (ICF)[1,2,3], radiation sources[4], plasma optics[5, 6] and laboratory astrophysics[7, 8]. Laser plasma instabilities[10, 11], especially stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS) and two-plasmon decay (TPD) instability, have been mainly considered in ICF with the incident laser intensity less than 1015 W/cm2[12,13,14]. The laser intensity may be of the order of 1016 or even 1017 W/cm in shock ignition[15,16,17,18,19], Brillouin amplification[20, 21] and the interactions of high-power laser with matter[22,23,24]. The parametric instabilities close to the regime of subrelativistic intensity need to be explored in depth
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