Role of Group Velocity Matching

Surprisingly, experiments in the Kapteyn-Murnane group at JILA, supported by our numerical simulations, revealed that isolated attosecond soft X-ray bursts can be generated efficiently with long-duration driver pulses at midinfrared wavelengths. Our theoretical analysis has shown that group velocity matching between the driving laser and the X-ray fields is a relevant factor in the isolation process. To study the effect on high harmonic generation, we have introduced a definition of the walk-off length in the nonperturbative intensity regime. Semiclassical predictions based on this definition are in excellent agreement with full quantum simulations - in collaboration with M. Murnane and H. Kapteyn (JILA).

C. Hernandez-Garcia et al., Opt. Express 25, 11855 (2017)
C. Hernandez-Garcia et al., New J. Phys. 18, 073031 (2016)
M.-C. Chen et al., Proc. Nat. Acad. Sci. 111, E2361 (2014)

Targeting Multiple Rescatterings

It has been previously proposed that at longer mid-infrared wavelengths multiple rescatterings of the electron from the parent ion play an important role. The detection of the number of these rescattering events however still poses a challenge to current experimental techniques. We have investigated the interrogation of high-order harmonic generation by a second pulse and identified signatures of multiple rescattering events in both the temporal and the frequency domain of the generated harmonic radiation.

M. Miller et al., Phys. Rev. A 90, 053409 (2014)

Enhancement of Dissociation

It is a long-standing assumption that strong laser pulses cannot induce significant vibrational excitation and dissociation of a molecule, unless the laser pulse is chirped to account for the anharmonicity of molecular vibrations. Our results of numerical simulations for the hydrogen molecular ion indicate that this conjecture may have to be revised. We find an enhancement of dissociation (solid line) over ionization (dashed-dotted line) by many orders of magnitude for interaction of the molecular ion with an unchirped ultrashort laser pulse at certain wavelengths in the infrared. The dissociation mechanism is related to an efficient excitation of molecular vibrations via two- and multiphoton transitions.

A. Picon et al., Phys. Rev. Lett. 109, 163002 (2012)
A. Picon et al., Phys. Rev. A 83, 023412 (2011)

JILA research highlight: Sizzling Vibrations.

Past Projects

Suppressed Molecular Ionization
We have explained the phenomenon of suppressed molecular ionization for a large range of molecules (up to C₆₀) using a S-matrix analysis.
J. Muth-Böhm et al., Phys. Rev. Lett. 85, 2280 (2000)
A. Jaron-Becker et al., Phys. Rev. Lett. 96, 143006 (2006)
J. Dura et al., J. Phys. Chem. 116, 2662 (2012)