Optimal Control of Laser-Plasma Instabilities Using Spike Trains of Uneven Duration and Delay: STUD Pulses

TL;DR

This paper introduces STUD pulses, a novel laser pulse modulation technique with uneven spike trains, to control plasma instabilities and improve laser fusion efficiency by minimizing backscatter and managing multi-beam interactions.

Contribution

The paper presents STUD pulses as an innovative method for controlling laser-plasma instabilities, surpassing traditional beam conditioning techniques with adjustable temporal and spatial modulation.

Findings

STUD pulses effectively minimize backscatter in plasma.

They allow control over multi-beam laser interactions.

Proper design of spikes reduces parametric instabilities.

Abstract

Adaptive methods of laser irradiation of plasmas are proposed consisting of deterministic, `on-off' amplitude modulations in time, and intermittently changing speckle-patterns. These laser pulses consist of a series of picosecond time-scale spikes in a spike train of uneven duration and delay (STUD pulses), in contrast to hydrodynamic-time-scale modulated, multi-nanosecond pulses for laser fusion. Properly designed STUD pulses minimize backscatter and tame any absorptive parametric instability for a given set of plasma conditions, by adjusting the modulation periods, duty cycles and spatial hot-spot-distribution scrambling-rates of the spikes. Traditional methods of beam conditioning are subsumed or surpassed by STUD pulses. In addition, STUD pulses allow an advance in the control of instabilities driven by spatially overlapped laser beams by allowing the spikes of crossing beams to be temporally staggered. When the intensity peaks of one fall within the nulls of its crossing beam, it allows an on-off switch or a dimmer for pairwise or multi-beam interactions.