Temporal evolution of electron-bunch length in macropulse of resonator-type free-electron lasers.

Microbunching caused by free-electron laser (FEL) interactions in an electron bunch deforms the overall bunch shape. Recent reports indicate the timing of the electron bunch overlapping with the FEL micropulse affects deformation in resonator-type FELs. The electron bunch shape is expected to change with the FEL micropulse energy because the FEL micropulse energy is enhanced within the electron beam macropulse; however, this has not yet been investigated.

Breakdown of argon by a train of high-repetition long-wave-infrared pulses from a free-electron laser oscillator.

This study presents an experimental demonstration of laser-induced breakdown in argon, employing a free-electron laser with a wavelength of 10 μm and a repetition rate of 2.856 GHz. Despite the fluence of individual laser pulses being an order of magnitude smaller than the breakdown threshold, cascade ionization developed in the pulse train, leading to breakdown.

Nonlinear compression of naturally down-chirped superradiance pulses from a free-electron laser oscillator by thick germanium plates.

Naturally down-chirped superradiance pulses, with mirco-pulse energy, peak wavelength, and micropulse duration of 40 µJ, 8.7 μm, and 5.1 optical cycles, respectively, emitted from a free-electron laser (FEL) oscillator were nonlinearly compressed down to 3.

Full characterization of superradiant pulses generated from a free-electron laser oscillator.

The detailed structure of superradiant pulses generated from a free-electron laser (FEL) oscillator was experimentally revealed for the first time. Owing to the phase retrieval with a combination of linear and nonlinear autocorrelation measurements, we successfully reconstructed the temporal waveform of an FEL pulse including its phase variation. The waveform clearly exhibits the features of a superradiant pulse, the main pulse followed by a train of sub-pulses with π-phase jumps, reflecting the physics of light-matter resonant interaction.