Gmh. Knippels et al., INTENSE FAR-INFRARED FREE-ELECTRON LASER-PULSES WITH A LENGTH OF 6 OPTICAL CYCLES, Physical review letters, 75(9), 1995, pp. 1755-1758
Second-order optical autocorrelation measurements are reported for a f
ar-infrared free-electron laser. Second-harmonic generation in an 840-
mu m-long CdTe crystal is used to provide the nonlinear autocorrelatio
n signal. At wavelengths of 10.4 and 24.5 mu m, FWHM pulse durations o
f 220 and 500 fs, respectively, are measured. In both cases this corre
sponds to six cycles of the optical field. The pulse energy ranges up
to 25 mu J. Evidence is presented that each pulse evolves into a train
of subpulses at large values of the cavity desynchronism.