Laser-induced gas breakdown by a train of femtosecond long-wave infrared FEL pulses

We observed the laser-induced breakdown of gases by a train of femtosecond long-wave infrared pulses generated from KU-FEL, the FEL oscillator at Kyoto University. We performed laser-induced breakdown experiments with different gas molecules and pressures and conducted simulations of cascade ionization. From the experimental and simulation results, we found that the breakdown was induced by cumulative cascade ionization by a train of FEL pulses.