Broadband Laser Smoothing in Inertial Confinement Fusion Facilities

Broadband laser sources offer laser–plasma instability (LPI) mitigation and faster laser-speckle smoothing that can outperform current smoothing systems. Broad bandwidth disrupts LPI growth via temporal incoherence and reduces nonlinear interaction intensity since the energy spreads across the broad spectrum. The broadband laser inherently reduces coherence time, and when coupled with dispersion, the time-averaged illumination smooths the random speckle field on an inertial confinement fusion (ICF) target. Smaller coherence time alone cannot reach adequate smoothing levels for nominal ICF target designs; therefore, future ICF facility upgrades require additional design improvements to achieve adequate smoothing levels and far-field spot-shape control. This talk explores these requirements to achieve adequate smoothing levels that outperform current ICF smoothing systems and far-field spot-shape control and the flexibility they offer for on-shot reconfiguration of design choices. The broadband laser sources are compatible with the random continuous polarization^[1],[2] device that provides instantaneous polarization smoothing in all directions of far-field speckle modulation with optional far-field spot envelope control via random birefringence patterns, which is realizable in a variety of birefringent materials.

[1] J.-M. G. Di Nicola et al., U.S. Patent Application Pub. No. US 2021/0239893 A1; Appl. No. 17/009,029; Provisional Application No. 62/967,774, filed Jan 30, 2020 (5 August 2021).

[2] J. A. Marozas et al., “Random Continuous Polarization Benefits for Inertial Confinement Fusion Facilities,” presented at the 65th Annual Meeting of the APS Division of Plasma Physics, Denver, CO, 30 October–3 November 2023.