Above-Threshold Ionization of Xenon by Chirped Intense Laser Pulses

We experimentally investigate above-threshold ionization of xenon subject to chirped intense laser pulses. While for few-cycle laser pulses free of chirp, the Freeman resonance narrow peaks in the photoelectron spectra become strongly suppressed, they will re-emerge for laser pulses with a certain chirp. Moreover, the position of the resonant peaks exhibits a strong dependence on the direction of the chirp. The experimental features can be understood by a two-step ionization process; that is, a multi-photon excitation plus subsequent ionization process.     

Experimental study on multiphoton ionization of Ar with high intensity short laser pulses

<正>We present high resolution photoelectron energy spectra from multiphoton ionization(MPI) of Ar subject to laser pulses with wavelength of 400 nm,pulse duration of 35 fs,and maximum intensity of 5×10~(13) W/cm~2.Ionizations into Ar~+ ~2P_(3/2) and ~2P_(1/2) channels are observed and distinct resonance structures are found in both ionization channels.The intensity dependence of the resonance structures is explained in terms of the mechanism of Freeman resonance,i.e.,transient resonances of alternating current (AC) Stark-shifted Rydberg states at specific intensities within the laser pulse.     

Multiphoton Ionization from Multiple Orbitals of N2 in Strong Laser Fields

We investigate multiphoton ionization （MPI） of N2 exposed to femtosecond laser fields at 400nm and 80Onto experimentally. Photoelectron energy spectra are measured with a high resolution photoelectron spectrometer at laser intensities up to 10^14 W/cm^2. Prominent resonant peaks observed at 400nm can be attributed to the resonance with molecular Rydberg states corresponding to different molecular orbitals, revealing the importance of the multiple orbitals contribution in strong field molecular dynamics.