Single-shot spectra of temporally selected micropulses from a   mid-infrared free-electron laser by upconversion
  We demonstrate the measurement of single-shot spectra of temporally selected micropulses from a mid-infrared (MIR) free-electron laser (FEL) by upconversion. We achieve the upconversion of FEL pulses at 11 \mu m using externally synchronized Nd:YAG or microchip laser pulses at 1064 nm to produce sum-frequency mixing (SFM) signals at 970 nm, which are detected by a compact CCD spectrometer without an intensifier. Our experimental system is very cost-effective, and allows us to obtain the laser spectra of selected micropulses at any temporal position within a single macropulse from an oscillator-type FEL. 
Xiaolong Wang, Takashi Nakajima, Heishun Zen, Toshiteru Kii, Hideaki   Ohgaki
physics.optics