Experimental Observation of Direct Particle Acceleration by Stimulated Emission of Radiation

We report the first experimental evidence for direct particle acceleration by stimulated emission of radiation. In the framework of this proof-of-principle experiment, a 45 MeV electron macrobunch was modulated by a high-power ${\mathrm{CO}}_2$ laser and then injected into an excited ${\mathrm{CO}}_2$ gas mixture. The emerging microbunches experienced a 0.15% relative change in the kinetic energy, in a less than 40 cm long interaction region. According to our experimental results, a fraction of these electrons have gained more than 200 keV each, implying that such an electron has undergone an order of magnitude of $2\times {10}^6$ collisions of the second kind.

Figure 1

Illustration of the light-electron-atom interaction. (a) The Franck-Hertz experiment. (b) The Latyscheff-Leipunsky experiment. (c) LASER. (d) PASER.

Figure 2

Schematic layout for the PASER experiment. The distance separating the wiggler and the PASER cell is about 2.5 m.

Figure 3

Raw video images from the electron energy spectrometer. Energy dispersion is in the horizontal direction. (a) Discharge is off in the PASER cell. (b) Discharge is on in the PASER cell. In both cases, $\sim 1.5\%$ peak-to-peak energy modulation was imparted.

Figure 4

Energy spectra of a single pair of shots with and without discharge and with $\sim 1.5\%$ peak-to-peak energy modulation. (a) Comparison of energy spectra discharge off/on. An energy increase of $\sim 200\mathrm{keV}$ is observed. (b) Spectra difference (discharge on minus discharge off).