Development of frequency-resolved optical gating for measurement of correlation between time and frequency of chirped FEL

Iijima, Hokuto; Hajima, Ryoichi; Minehara, Eisuke; Nagai, Ryoji; Nishimori, Nobuyuki

A femtosecond infrared-chirped FEL is an effective way of dissociating molecules without the intramolecular vibrational redistribution. At Japan Atomic Energy Agency (JAEA), an energy recovery linac (ERL) has been investigated to provide a high power FEL at far-infrared region. Normally the long-pulse electron beam is operated by the ERL; therefore the high-power chirped pulse can be generated. Until now, the distribution of frequency in the FEL pulse was measured to be = 14% with the wavelength of 23 m and the pulse width of 320 fs at FWHM via FR-SHG autocorrelator. However the variation of frequency during the pulse was not measured. In order to measure the correlation between time and frequency in the chirped pulse directly, we have started to construct an FEL transport system and the frequency-resolved optical gating. Now we are measuring basic parameters of the chirped pulse (beam size, power and so on) in the experimental room.