Generation of a self-chirped laser pulse has been demonstrated with a free-electron laser (FEL) oscillator. A laser pulse having a frequency chirp of 14.3% and a time duration of 319 fs was demonstrated at the JAERI-FEL (Fig. 5-9).
It is known that coherent control of laser pulses can effectively synthesize and decompose material. Fig. 5-10 shows an example: dissociation of a molecule through vibrational excitation by a laser pulse. This type of dissociation can be conducted efficiently if the laser pulse has frequency chirp matching the non-harmonic mode of the potential ladder. A laser pulse with a frequency chirp large enough for such an application however has never been obtained in a FEL. The interaction of a laser field and electrons in a FEL was analyzed, and it was concluded that the frequency chirp exceeds 10% in a high-gain, short-pulse FEL oscillator. An experiment at the JAERI-FEL (Fig. 5-11) demonstrated a chirped-pulse as predicted by the analysis.
The JAERI-FEL group has developed a high-power FEL driven by a superconducting linear accelerator. In 2000, this FEL achieved lasing at 2.34 kW, the highest power in the world at that time. Also in 2002, an energy-recovery system was constructed that improves the conversion efficiency from utility electric power to laser power. Chirped-pulse generating FELs will extend the applications of high-power FELs into industrial fields such as decomposition of toxic materials and synthesis of useful molecules. |
