High-power, low-coherence laser pulse generation via plasma-based optical modulation

High-power, low-coherence laser pulses are essential for suppressing laser–plasma instabilities (LPIs) in inertial confinement fusion (ICF). However, it remains challenging for conventional optical techniques to generate high-power, low-coherence lasers with a fractional bandwidth Δω/ω0 exceeding 1%. Here, we propose and numerically validate a plasma-based optical modulation scheme for generating high-power, low-coherence laser pulses with an ultrabroad bandwidth of Δω/ω0 ∼ 5%. This scheme utilizes two laser pulses co-propagating in an underdense plasma: an intense femtosecond driver laser pulse that excites an electron plasma wave, and a subsequent picosecond signal pulse that is spectrally broadened via forward stimulated Raman scattering within the electron plasma wave. More importantly, when the initial signal pulse already possesses a continuous spectrum with a bandwidth Δω larger than the electron plasma frequency ωpe, the modulated signal pulse exhibits not only a broadened continuous spectrum, but also a significantly shortened coherence time, which is nearly an order of magnitude shorter than that achieved using an initially monochromatic signal pulse. For high-power ICF lasers, the coherence time is a more critical parameter than the bandwidth in evaluating their capability to suppress LPIs. Furthermore, this plasma-based optical modulation scheme achieves a high energy conversion efficiency (η ≳ 99%) and is applicable to frequency-doubled or -tripled laser pulses. Therefore, it offers a promising pathway to the generation of high-power, low-coherence laser pulses for suppressing LPIs in ICF.