Spectral phase control for optimized ionization injection in laser wakefield acceleration

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Backhouse, M. P. and Dickson, L. T. and Moulanier, I. and Massimo, F. and Cobo, C. C. and Filippi, F. and Gustafsson, C. and Lofquist, E. and Svendsen, K. and Streeter, M. J. V. and Shalloo, R. J. and Vasilovici, O. and Ballage, C. and Dann, S. J. D. and Murphy, C. D. and Najmudin, Z. and Dobosz Drufrenoy, S. and Lundh, O. and Cros, B. (2025) Spectral phase control for optimized ionization injection in laser wakefield acceleration. Physical Review Accelerators and Beams, 28 (12). 121301. ISSN 2469-9888 (https://doi.org/10.1103/9gjq-htzn)

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Abstract

Generating narrow energy spread beams from laser wakefield accelerators with minimal dark current is important for many applications. We present an automated experiment using Bayesian optimization to control the laser spectral phase and focal position, achieving significant enhancement of the beam quality. Starting from a broadband spectrum, the optimized configuration achieved low-energy spread with negligible dark current above 20 MeV. Particle-in-cell simulations reveal that fine control over the laser spectral phase, particularly third-order dispersion, directly impacts the timing and localization of ionization injection due to its effect on the initial laser intensity envelope and its subsequent evolution. A positively skewed temporal profile enhances the plasma potential depth at the right location, enabling localized injection and reducing the energy spread and dark current. These findings highlight the impact of algorithmic optimization and the powerful, underutilized role of temporal shaping in beam quality control.

ORCID iDs

Backhouse, M. P., Dickson, L. T. ORCID logoORCID: https://orcid.org/0000-0002-5200-7525, Moulanier, I., Massimo, F., Cobo, C. C., Filippi, F., Gustafsson, C., Lofquist, E., Svendsen, K., Streeter, M. J. V., Shalloo, R. J., Vasilovici, O., Ballage, C., Dann, S. J. D., Murphy, C. D., Najmudin, Z., Dobosz Drufrenoy, S., Lundh, O. and Cros, B.;
CORE (COnnecting REpositories)