The role of focusing geometry in MeV x-ray production from petawatt laser–solid interaction

Relativistic laser–plasma interactions provide a compact and flexible route to generating bright, ultrashort pulses of MeV x rays, with applications in high-energy density science, nuclear physics, and radiography. Despite extensive study of intensity scaling in laser-driven electron acceleration, the role of focusing geometry and focal-volume effects in MeV radiation production remains insufficiently understood. Here, we present experimental and kinetic simulation results from the Texas Petawatt Laser (120 J, 140 fs) in which the focusing geometry (f/3 or f/1.5) is varied, while the laser energy and pulse duration are fixed. Experimentally, the f/3 geometry produces approximately three times more MeV radiation than the f/1.5 geometry, despite its twofold lower nominal vacuum intensity. This result is based on the time-integrated radiation per unit solid angle, as measured along the diagnostic line of sight. Three-dimensional particle-in-cell simulations reproduce this trend when a modest (10s of μm) effective focal plane shift is introduced, demonstrating that relativistic laser–plasma coupling is highly sensitive to focal geometry in the presence of a preplasma. This behavior is consistent with differences in interaction length and effective intensity at the critical surface between the two configurations. The sensitivity of the tightly focused f/1.5 configuration (zR≈ 5 μm) reflects the combined influence of thermal lensing and an extended preplasma, while the f/3 geometry (zR≈ 80 μm) remains comparatively robust. These results demonstrate a breakdown of conventional intensity scaling and identify focusing geometry as a critical control parameter for MeV electron and x-ray generation at petawatt powers. Implications for laser–plasma-based radiographic facilities are also discussed.

Authors

Institutions

Publication Details

Journal
Physics of Plasmas
Published
2026-04-01
DOI
https://doi.org/10.1063/5.0316883
Primary Topic
Laser-Plasma Interactions and Diagnostics
Type
article
Field-Weighted Citation Impact
0.00

Funders

Controls
|||
ALL TIME
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
article

The role of focusing geometry in MeV x-ray production from petawatt laser–solid interaction

A. Van Pelt, James Hunter, Hernan Quevedo, D. C. Gautier et al.
Physics of Plasmas
Laser-Plasma Interactions and Diagnostics
article

The role of focusing geometry in MeV x-ray production from petawatt laser–solid interaction

A. Van Pelt, James Hunter, Hernan Quevedo, D. C. Gautier, D. J. Stark, Sandra Bruce, J. Strehlow, T. Ditmire, A. Helal, J Twardowski, A. Bogale, Scott V. Luedtke, S. Palaniyappan, Alexey Arefiev, K. D. Meaney, Kavin Tangtartharakul, D. Rusby, L. Tyler Mix, R. Nedbailo, B. J. Albright, Rebecca Fitzgarrald, F. N. Beg, T. A. Coffman, C-K Huang, Yong Ho Kim, C.-S. Wong, A. G. R. Thomas, E. A. Chowdhury, J. C. Fernández, M. M. Spinks, C. Herrera-Hernandez, J. L. Schmidt
article en

Abstract

Relativistic laser–plasma interactions provide a compact and flexible route to generating bright, ultrashort pulses of MeV x rays, with applications in high-energy density science, nuclear physics, and radiography. Despite extensive study of intensity scaling in laser-driven electron acceleration, the role of focusing geometry and focal-volume effects in MeV radiation production remains insufficiently understood. Here, we present experimental and kinetic simulation results from the Texas Petawatt Laser (120 J, 140 fs) in which the focusing geometry (f/3 or f/1.5) is varied, while the laser energy and pulse duration are fixed. Experimentally, the f/3 geometry produces approximately three times more MeV radiation than the f/1.5 geometry, despite its twofold lower nominal vacuum intensity. This result is based on the time-integrated radiation per unit solid angle, as measured along the diagnostic line of sight. Three-dimensional particle-in-cell simulations reproduce this trend when a modest (10s of μm) effective focal plane shift is introduced, demonstrating that relativistic laser–plasma coupling is highly sensitive to focal geometry in the presence of a preplasma. This behavior is consistent with differences in interaction length and effective intensity at the critical surface between the two configurations. The sensitivity of the tightly focused f/1.5 configuration (zR≈ 5 μm) reflects the combined influence of thermal lensing and an extended preplasma, while the f/3 geometry (zR≈ 80 μm) remains comparatively robust. These results demonstrate a breakdown of conventional intensity scaling and identify focusing geometry as a critical control parameter for MeV electron and x-ray generation at petawatt powers. Implications for laser–plasma-based radiographic facilities are also discussed.

Physics of PlasmasVol. 33(4)
Lawrence Livermore National Laboratory (US), Los Alamos National Laboratory (US), William & Mary (US), University of Michigan (US), University of California San Diego (US), Optical Sciences (United States) (US), The Ohio State University (US), The University of Texas at Austin (US)
National Science Foundation, Fusion Energy Sciences, Laboratory Directed Research and Development
Affordable and clean energy
Openalex Percentile: Top 22%
Laser-Plasma Interactions and Diagnostics
DOIOpen Access PDFOpenAlex
AI Navigator

Ask Laika to Summarize, Analyze, and Connect papers live on the map.

Summarize Papers & Methodologies

Extract key findings, datasets, and comparative methods across publications.

Benchmark Rankings & Visual Analytics

Rank top research institutions, authors, funders, topics, and journals by Field-Weighted Citation Impact (FWCI) and paper volume with instant charts.

Connect Distant Disciplines

Bridge topological clusters on the map to find hidden collaborative intersections.