Using High Harmonic Generation Spectra to Study Returning Electronic Wavepackets Exposed to a Strong Laser Field

When an atom or molecule is exposed to a strong laser field, ionization occurs via absorption of one or more photons. Once ionized, the electron, caught in an oscillating field, may be driven back to the ionic core and either recombine with the parent ion, elastically re-scatter off it, or inelastically re-scatter. This elastic re-scattering phenomena has lead to the observation of an enhancement within the Above Threshold Ionization (ATI) spectra of noble gases at very specific field intensities along the laser polarization. Many theories have been provided over the last three decades, but the cause of this enhancement is still not very well understood. Understanding the behavior of the evolving electronic wavepacket within the recombination channel could provide key insights to the development of the enhancement. Here, we present a time-energy Fourier analysis of calculated High Harmonic Generation (HHG) spectra. We show clear cycle to cycle HHG yield increases at specific laser intensities.