Abstract

In this talk, we present experimental and theoretical results on ultrashort harmonic generation in gases using an amplified Ti:sapphire laser with a 25fs pulsewidth. [1] The bandwidth of the pulses is 32 nm, centred at a wavelength of 805 nm, and the laser system can provide up to 70 mJ of energy per pulse at a 10Hz repetition rate. The laser beam is focused by a curved mirror onto a gas target to generate the high harmonics, and the spectra were taken using a grazing-incidence soft-x-ray spectrometer. The ultrashort nature of our excitation pulses (10 optical cycles FWHM) implies that at the half maximum position of the temporal pulse envelope, the laser intensity change by more than 25% during a single cycle. This defies the adiabatic assumption, which suggests that the atomic dipole moment undergoes quasi-periodic motion from cycle to cycle, with no dependence on the history of the pulse.

© 1996 Optical Society of America