Absolute keV X-ray yield and conversion efficiency in over dense Si sub-petawatt laser plasma

Ryazantsev, Sergey N. and Martynenko, Artem S. and Sedov, Maksim V. and Skobelev, Igor Yu. and Mishchenko, Mikhail D. and Lavrinenko, Yaroslav S. and Baird, Christopher D. and Booth, Nicola and Durey, Phil and Döhl, Leonard N. K. and Farley, Damon and Lancaster, Kathryn L. and McKenna, Paul and Murphy, Christopher D. and Pikuz, Tatiana A. and Spindloe, Christopher and Woolsey, Nigel and Pikuz, Sergey A. (2022) Absolute keV X-ray yield and conversion efficiency in over dense Si sub-petawatt laser plasma. Plasma Physics and Controlled Fusion, 64 (10). 105016. ISSN 0741-3335 (https://doi.org/10.1088/1361-6587/ac8b33)

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Abstract

Laser-produced plasmas are bright, short sources of x-rays commonly used for time-resolved imaging and spectroscopy. Their usage implies accurate knowledge of laser-to-x-ray conversion efficiency (CE), spectrum, photon yield and angular distribution. Here, we report on soft x-ray emission in the direction close to the target normal from a thin Si foil irradiated by a sub-PW picosecond laser pulse. These absolute measurements cover a continuous and broad spectral range that extends from 4.75 to 7.3 Å (1.7-2.6 keV). The x-ray spectrum consists of spectral line transitions from highly charged ions and broadband emission with contributions from recombination and free-free processes that occur when electrons decelerate in plasma electromagnetic fields. Angular distribution of the emission was investigated via particle-in-cell simulations, which allowed to estimate the yield into the full solid angle. We find that experimental and simulation estimations of laser to free-free emission CE are in good agreement.

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