Gamma-ray photons with energy >9  MeV were produced when second-harmonic-generated laser light (3 eV) inverse-Compton-scattered from a counterpropagating relativistic (~450  MeV) laser-wakefield-accelerated electron beam. Two laser pulses from the same laser system were used: one to accelerate electrons and one to scatter. Since the two pulses play very different roles in the γ-ray generation process, and thus have different requirements, a novel laser system was developed. It separately and independently optimized the optical properties of the two pulses. This approach also mitigated the deleterious effects on beam focusing that generally accompany nonlinear optics at high peak-power levels.

Compact source of narrowband and tunable X-rays for radiography" (2015). Donald Umstadter Publications. 105.

The Compton scattering cross section from 4 He has been measured with high statistical accuracy over a scattering angle range of 40 •-159 • using a quasi-monoenergetic 61-MeV photon beam at the High Intensity Gamma Ray Source (HIγS). The data are interpreted using a phenomenological model sensitive to the dipole isoscalar electromagnetic polarizabilities (αs and βs) of the nucleon. These data can be fit with the model using values of αs and βs that are consistent with the currently accepted values. These data will serve as benchmarks of future calculations from Effective Field Theories and Lattice QCD.