GENERATION OF FREQUENCY-CHIRPED PULSES IN THE FAR-INFRARED BY MEANS OF A SUBPICOSECOND FREE-ELECTRON LASER AND AN EXTERNAL PULSE SHAPER

The generation of frequency-chirped optical pulses in the far-infrared is reported. The pulses are produced by the free-electron laser FELIX . The chirp is induced by means of an external shaping device consisti ng of a grating and a telescope. The shaper is based on reflective opt ics to permit operation in a wide spectral range. The present experime nts were made at 8.2 mu m wavelength. The fwhm duration of the inciden t pulse was 0.50 ps, which corresponds to a bandwidth of 2.2%. It has been checked that a linear chirp is produced, for the case that the fr equency increases from the leading edge of the pulse to the trailing e dge, as well as for the reverse case. This is accompanied by an increa se of the fwhm pulse duration which ranges up to 16.5 ps.