Simultaneous amplification and shaping of excimer lasers using Stimulated Brillouin Scattering in the strongly damped limit

Abstract

Attaining practical Inertial Fusion Energy (IFE) depends on how efficiently one can couple the driver energy to the nuclear fusion fuel for compression and ignition. While the excimer lasers provide an efficient alternative compared to existing laser technology, it is unclear how the lasers can be harnessed to form a pulse with desired pulse shape and intensity. Stimulated Brillouin Scattering (SBS) provides a path to compressing long, energetic pulses to short intense ones. We consider the equations governing SBS in the Strongly Damped Limit (SDL) and find that it is possible to almost completely specify the final pulse shape by providing an appropriate initial seed pulse. We provide analytic expressions for reverse-engineering the initial seed shape and delineate physical limits concerning the prepulse level.

Figures (7)

• Figure 1: DWG Schematics . Top: an undepleted pump (Dark Blue) and a weak seed pulse (light orange interacts in a SBS active medium (Green). The amplified seed (Dark orange) is both amplified and temporally shaped over time. Bottom: seed(orange) and pump evolution in the moving frame, progressing from right to left.
• Figure 2: Seed and Pump intensity evolution in the Strongly Damped limit (a-b). Seed and pump pulse intensity evolution over time (a) . Seed(Orange) and Pump(Blue) initially ($\tau=0$, dashed) and at $\tau=2$ (solid). (b) magnificed version of (a) showing the seed pulse leading edge evolution and the seed pulse front velocity $\partial_\tau \zeta_{\rm lin}$, with inset showing pump evolution
• Figure 3: Asymptotic seed shape evolutions for (a)gaussian, (b) 4th order supergaussian, (c) exponential , (d) lorentzian at $\tau=0$(solid red), $\tau=5$ (solid green) and $\tau=10$ (solid blue). Black dashed lines: analytic prescription (Eq. \ref{['eq:asymptotic']}).
• Figure 4: Effect of noise on pulse amplification. (a-b) "clean" and (c-d) "noisy" pulse amplification. (a,c) initial seed profiles in logarithmic scale. Insets: profile in linear scale. (b,d) seed (solid orange line) and pump (solid blue line) profile after $\tau=15$. Dash-dotted(Dashed) black lines: predicted asymptotic evolution of the main pulse(pedestal). Parameters in the main text.
• Figure 5: Piecewise prescription of seed (a) and its asymptotic evolution(b). Dashed (Dash-Dotted) Lines: $\zeta_1=-2.5$, $\zeta_2=-1.25$. Dotted line in (b): asymptotic prescription. Different Colored lines in (b): amplified pulse at different propagation length $\tau_0=0$(blue), $\tau_1=5$(red), $\tau_2=10$(yellow), $\tau_3=15$(purple).