Fig. 1. Diagram of the laser Compton scattering (LCS) process

Fig. 2. Diagram of key components in Geant4 model

Fig. 3. Comparison diagram of the variation of scattered gamma spectra with a circular electron beam size in transverse (a) and longitudinal (b) dimensions (color online)

Fig. 4. Variation of the scattered gamma spectra with the electron beam in horizontal dimension (color online)

Fig. 5. Variations of the scattered gamma spectra with by a circular electron beam in vertical (a), longitudinal (b) dimension (color online)

Fig. 6. Diagram of the SLEGS beamline station

Fig. 7. Comparison diagram of the experimentally measured energy spectra measured at different collision angles θi (color online)

Fig. 8. Comparison diagram of energy spectrum between the simulation and experimentally measured at the collision angle θi of 124° (color online)

Fig. 9. Illustration of scatter plot and the deviation between the experimentally measured and simulated energy spectra with respect to the electron beam horizontal dimension σx and the electron beam energy Ee and diagram of best fitting result (color online)