Stable and Tunable MeV γ-ray Generation via Dual-Laser Inverse Thomson Scattering from a Laser–Plasma Accelerator

Inverse Thomson scattering from laser–plasma accelerators offers a pathway to compact, tunable MeV γ-ray sources for reduced-dose radiography and nuclear resonance fluorescence (NRF)–based isotope identification, but photon yield and spectral quality are often limited by constraints on interaction geometry and scatter-laser tunability. Here we demonstrate a tunable MeV γ-ray source based on a dual-laser inverse Thomson scattering configuration driven by a 100-TW laser–plasma accelerator. Electron beams tunable from 122 to 204 MeV with < 5 mrad divergence and < 1 mrad pointing stability generate γ rays with peak energies from 276 keV to 1.2 MeV and yields up to 2 × 10 7 photons per shot. By independently controlling the interaction position and the scatter-pulse duration, we experimentally match the scatter pulse to the walk-off-limited interaction length. Extending the scatter pulse to 200 fs increases photon production by approximately 15% while maintaining operation in the linear Thomson regime, thereby preserving narrow spectral bandwidth and controlled radiation divergence. Radiographic characterization demonstrates MeV-level penetration and ≈ 0.1 mm spatial resolution. Stable operation is sustained over multi-hour timescales across multiple days. These results demonstrate that interaction-length optimization provides a scalable strategy for improving photon yield, spectral control, and operational stability in compact laser–plasma-accelerator–driven γ-ray sources.