Abstract
We exploit high-order harmonic generation spectroscopy at the caustics of the recombining electron wave-packet as a method for directly comparing experimental spectra with ab-initio theories. Experimental results in xenon and comparison with ab-initio time-dependent configuration-interaction singles calculations allowed to assess the role of the wave-packet enhancement during the giant resonance. Results in argon show that this technique can also be applied to other targets.
Highlights
Direct comparison of high-order harmonic generation (HHG) spectra with ab-initio singleatom theories is often hampered by many factors, such as spatial phase-matching and averaging effects which often reshape the experimental spectrum in a hardly predictable way
When the HHG process is driven by a field with a strong component of wavelength λ and a weaker second harmonic, two caustics appear in the HHG spectrum
A careful analysis of the results presented in our previous paper [2] and a comparison with ab-initio and quantitative rescattering (QRS) theories allows to assess the role of the electronic wave-packet enhancement in the xenon giant resonance
Summary
Direct comparison of high-order harmonic generation (HHG) spectra with ab-initio singleatom theories is often hampered by many factors, such as spatial phase-matching and averaging effects which often reshape the experimental spectrum in a hardly predictable way. By probing the signal at these two spectrally separated caustics, it is possible to isolate and enhance a single recombination event for each cycle of the laser field, overcoming the problem of determining which trajectory is contributing to the process.
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