ABSTRACT
Fine Mechanics, Chinese Academy of Sciences, P.O. Box 800-211, Shanghai 201800, China department of Physics, East China Normal University, Shanghai 200032, China
Abstract. The evolution of the electron density of the plasma column generated by the self-channelling of femto-second laser pulses in the air was investigated. Based on the typical pump-probe technique, the electron density in the plasma channel can be extracted from the diffraction pattern of the probing laser beam. By employing a pump-probe back longitudinal diffractometer, the measurable electron density scale was extended to 1015 cm"3. The ionization and decaying process on the hundreds of pico-second time scale was measured. A novel technique termed as linear-chirped longitudinal spectral diffractometer is developed. Via this method the evolution of the density on a time scale of tens of femto-seconds can be re-constructed from the spectra of the diffraction pattern of a linearchirped laser pulse. By this method we realized the single-shot measurement of the electron density evolution of femtosecond time scale.
