TEMPORAL CHARACTERIZATION OF MID-IR FREE-ELECTRON-LASER PULSES BY FREQUENCY-RESOLVED OPTICAL GATING

We performed what we believe are the first practical full-temporal-cha racterization measurements of ultrashort pulses from a free-electron l aser (FEL). Second-harmonic-generation frequency-resolved optical gati ng (FROG) was used to measure a train of mid-IR pulses distorted by a saturated water-vapor absorption line and showing free-induction decay . The measured direction of time was unambiguous because of prior know ledge regarding free-induction decay. These measurements require only 10% of the power of the laser beam and demonstrate that FROG can be im plemented as a pulse diagnostic simultaneously with other experiments on a FEL. (C) 1997 Optical Society of America.