Pulse width effects on Raman backward laser amplification

Abstract

The effects of the longitudinal pulse width were studied in Raman backward amplification (RBA) of laser pulses in plasmas. In RBA systems, which utilize Raman backscatter in plasmas, it is generally required that a long pump laser pulse, whose longitudinal pulse duration is typically tens of picoseconds, propagates more than a few millimetres of gas jet or capillary plasmas. However, from the experimental point of view, a short propagation distance of the pump pulse is more desirable to avoid various technical difficulties and physical instabilities. In this paper, the change in the characteristics of RBA systems for varying widths of the pump pulse is studied by fluid and kinetic simulations. The effects of the initial width of the seed pulse are also addressed.

Demonstration of detuning and wavebreaking effects on Raman amplification efficiency in plasma

“…However, if the original seed pulse is longer or the order on the amplified pulse, then only a small fraction of the seed pulse plays a role in BRA. The back part of the seed is shadowed by its front and does not affect amplification [32,33]. In this case, the effective seed pulse amplitude eff is a useful concept [32].…”

Multifrequency Raman amplifiers

“…In particular, what emerged from these studies of physical effects were techniques, exploiting the laser bandwidth, designed to improve the operation of Raman plasma amplifiers in different regimes. The exploiting of the bandwidth, and in particular chirping the frequency, underlies a number of other studies as well [17][18][19][20][21][22][23]. Chirping the pump laser, together with exploiting a density gradient, can suppress noise and precursors [13].…”

Multi-frequency Raman amplifiers

“…In particular, what emerged from these studies of physical effects were techniques, exploiting the laser bandwidth, designed to improve the operation of Raman plasma amplifiers in different regimes. The exploiting of the bandwidth, and in particular chirping the frequency, underlies a number of other studies as well [17][18][19][20][21][22][23]. Chirping the pump laser, together with exploiting a density gradient, can suppress noise and precursors [13].…”