{'fraction_non_alphanumeric': 0.02972027972027972, 'fraction_numerical': 0.0008741258741258741, 'mean_word_length': 5.735294117647059, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Experimental observation and investigation of energy exchange between an electron beam and counterpropagating laser beams in a Compton-scattering free-electron-laser scheme.

We report the observation and investigation of synchronous energy exchange between nonrelativistic electrons and the ponderomotive (beat) force of two counterpropagating intense pulsed CO/sub 2/ laser beams, operating at different frequencies in a stimulated Compton-scattering scheme. The interaction occurred in the nonlinear (trapping) regime, the physics of which is the same as that which occurs in laser accelerators and efficiency-enhanced free-electron lasers (FEL's) with long wigglers. The experiment is a first demonstration of the principle of inverse FEL acceleration and electromagnetic pump FEL operation in the nonlinear (trapping) regime. It can also be described as a demonstration of a ''traveling beat-wave'' Kapitza-Dirac effect in the nonlinear regime. Two different mechanisms of enhanced energy transfer were observed: electron trapping and phase-area displacement. Experimental results and computer simulations of both mechanisms are presented.