Time-Resolved Dynamics in N ₂ O ₄ Probed Using High Harmonic Generation

Abstract

The attosecond time-scale electron-recollision process that underlies high harmonic generation has uncovered extremely rapid electronic dynamics in atoms and diatomics. We showed that high harmonic generation can reveal coupled electronic and nuclear dynamics in polyatomic molecules. By exciting large amplitude vibrations in dinitrogen tetraoxide, we showed that tunnel ionization accesses the ground state of the ion at the outer turning point of the vibration but populates the first excited state at the inner turning point. This state-switching mechanism is manifested as bursts of high harmonic light that is emitted mostly at the outer turning point. Theoretical calculations attribute the large modulation to suppressed emission from the first excited state of the ion. More broadly, these results show that high harmonic generation and strong-field ionization in polyatomic molecules undergoing bonding or configurational changes involve the participation of multiple molecular orbitals.

Influence of phase matching on the Cooper minimum in Ar high-order harmonic spectra

“…For example, the recombination radiation contains information about the internuclear distance of a diatomic source medium which can be described by a "two center interference model" [4,5]. Different ionization channels in the form of close lying molecular orbitals have also been found to lead to interference features in harmonic spectra [6][7][8][9].…”

Probing and extracting the structure of vibratingSF6molecules with inner-shell photoelectrons

“…Apart from the more traditional approaches based on x-ray diffraction [2,6] and ultrafast electron diffraction (UED) [7], methods based on the recollision phenomena with intense driving lasers have been proposed and successfully tested on simple molecules. We mention here high-order harmonic-generation (HHG) spectroscopy [8][9][10][11][12] and laser-induced electron diffraction (LIED) [9,[13][14][15][16][17][18]. Time-resolved photoelectron spectroscopy (TRPES) and time-resolved molecular-frame photoelectron angular distribution (TRMFPAD) measurements proposed recently [19,20] are capable of imaging valence-electron dynamics and atom motion during a chemical reaction.…”

Exchange and polarization effect in high-order harmonic imaging of molecular structures

“…Additional opportunities for imaging arise in pump-probe-type experiments, with HHG used as a probe of nuclear dynamics induced by an ultrashort pump (see, e.g., [5,6]). The pump-probe setup in harmonic generation can also be used to follow electronic rearrangements induced by the underlying nuclear dynamics at conical intersections [7].…”

“…The participation of multiple ionic states not only during recombination, but also at all steps of the harmonic generation process [6,12,[15][16][17][18][19], introduces additional opportunities for dynamic imaging. For example, it opens a route to following attosecond dynamics of holes between ionization and recombination [15][16][17][18].…”