Advantages to a diverging Raman amplifier

Abstract

The plasma Raman instability can efficiently compress a nanosecond long high-power laser pulse to sub-picosecond duration. Although, many authors envisaged a converging beam geometry for Raman amplification, here we propose the exact opposite geometry; the amplification should start at the intense focus of the seed. We generalise the coupled laser envelope equations to include this non-collimated case. The new geometry completely eradicates the usual trailing secondary peaks of the output pulse, which typically lower the efficiency by half. It also reduces, by orders of magnitude, the initial seed pulse energy required for efficient operation. As in the collimated case, the evolution is self similar, although the temporal pulse envelope is different. A two-dimensional particle-in-cell simulation demonstrates efficient amplification of a diverging seed with only 0.3 mJ energy. The pulse has no secondary peaks and almost constant intensity as it amplifies and diverges.

Preparations for a European R&D roadmap for an inertial fusion demo reactor

“…Our consortium is also actively pursuing the physics of laser-plasma amplifiers as a route to overcome the need for expensive grating compressors [ 42 , 43 ]. There are new advances in laser technology based upon optical parametric chirped pulse amplification (OPCPA) that might also lead to multi-kJ petawatt-scale ultra-violet pulses.…”

Anisotropic heating and magnetic field generation due to Raman scattering in laser-plasma interactions

“…Much of the attention drawn to SRS is related to inertial fusion, where the plasma waves associated with the SRS instability can preheat the plasma electrons [28][29][30][31]. Furthermore, there is a more recent interest in using plasmas as a medium for amplification of electromagnetic pulses through the SRS mechanism [32][33][34][35][36][37].…”

Joule-Level High-Efficiency Energy Transfer to Subpicosecond Laser Pulses by a Plasma-Based Amplifier

“…The way the plasma responds to an external excitation and couples to it, fully characterizes the performances of a plasma amplifier. The schemes proposed and studied so far exploiting an electron or ion response of the plasma (resonant Raman [1][2][3], chirped pump Raman [4,5], Raman with flying focus [6], diverging Raman [7], multi-frequency Raman [8], plasma wave seed for Raman [9], single-pulse Raman [10], stronglycoupled Brillouin [11], single-pulse Brillouin [12], fewcycle laser amplification by Brillouin [14]) have explored different parameter ranges and beam configurations in order to optimize (or minimize) a particular aspect of the amplification. Each scheme, according to which type of plasma excitation is exploited, has been put forward as the most appropriate for a specific purpose.…”

“…Among the schemes cited above, many of them, theoretically and/or numerically explored, have predicted very high efficiency. For example, amplification of a 0.3mJ seed pulse above 1.2 J is predicted using the diverging scheme [7], while a 15 J -50 fs could be amplified to 5 kJ -60 fs from a 10 kJ -1 ns pump in a optimized plasma amplifier [25]. However, experimental results are very rare and the transferred energies and efficiencies are much lower.…”