Post-Chirped-Pulse-Amplification Pulse Compression for High Energy Laser Systems

Project Overview

The on-shot yields of relativistic laser-plasma interactions are reliant on the capability of the dedicated laser system to provide sufficient peak power to the target. Upgrading an existing laser to meet such needs is often a costly, challenging process that necessitates a substantial expansion of the final amplifier, transport beamline, and compressor to allow for a safe increase in the pulse energy. In this work, we investigate an alternative, cost-effective method to enhance the peak power, instead through a further compression of the existing laser-pulse energy within a pulse duration much shorter than would otherwise be allowed by the chirped pulse amplification (CPA) architecture and laser gain material. This post-CPA pulse-compression technique takes advantage of the high laser intensities in the final transport beamline before the target to induce a strong nonlinear response in a thin optical material. This low-cost, highly transmissive component can be modified to result in a homogeneous broadening of the spectrum, even with a heavily distorted beam profile. A corrector plate is then bonded to the surface to preserve the spatio-temporal fidelity of the laser, and the induced chirp within the pulse is compensated using a chirped mirror compressor. The compact system is easily scalable and can be attached to the back end of an existing laser system—without requiring any adjustments to the CPA architecture—to increase the peak power by factors of two to three per pass.

During this investigation, we designed a post-CPA pulse compression system using an in-house 4D-modeling capability and implemented the setup in an existing LLNL laser laboratory. We have demonstrated spatially homogeneous spectral broadening and pulse compression that resulted in a peak power enhancement of 2.7 times in a single pass. Furthermore, we have demonstrated self-compression of an ultrashort laser pulse operating in the wavelength regime of the next-generation, LLNL-designed big-aperture thulium (BAT) laser concept. Overall, this feasibility study has resulted in a simple and cost-effective method to enhance laser pulse peak power and has enabled additional avenues for exploration on optimizing the post-CPA pulse compression technique.

Mission Impact

This feasibility study directly addresses the lasers and optical science and technology core competency through research and development of a technique that enhances the performance of high power, state-of-the-art laser systems. Both existing and future lasers could utilize this now validated concept, which can be scaled in both peak and average power, to support the study of laser-plasma interactions by enabling two-to-three times higher peak powers using current CPA technology. Furthermore, the spatially homogeneous nonlinear broadening and compression resulting from the low-cost, compact optical setup enables LLNL's BAT laser technology to reach the challenging pulse duration regimes required for laser wakefield acceleration (LWFA), and thus is synergistic with broader LLNL and DOE interests in accelerator science for HED science and national-security applications. This work has produced a US/PCT patent application filing and has prompted collaborations between Advanced Photon Technologies (APT) and other internal groups at LLNL, including one that supports a core competency in optical materials through a new NIF optics fabrication capability of Sol-Gel anti-reflective coatings on polymer optical components.

Publications, Presentations, and Patents

Tamer, I., Lawrence Livermore National Security, LLC, “Spatially Homogeneous Nonlinear Spectral Broadening.” US Patent Application PCT/US2021/072670 Filing date: December 1, 2021.