Above-Threshold Ionization with subpicosecond laser pulses.
01 January 1987
Above Threshold Ionization (ATI) is investigated in xenon with pulses of light at 616 nm ranging from 15 psec to 0.4 psec. Large energy shifts and pronounced broadenings in the ATI peaks are observed as a function of decreasing pulsewidths. For pulsewidths less than 1 psec, we have observed a new phenomenon: the individual ATI peaks break up into a narrow fine structure. This fine structure appears to be the result of resonance enhancements in the ionization probability produced by ponderomotive shifts of the various excited states of xenon.