Probing Polar Molecules with High Harmonic Spectroscopy

Abstract

We bring the methodology of orienting polar molecules together with the phase sensitivity of high harmonic spectroscopy to experimentally compare the phase difference of attosecond bursts of radiation emitted upon electron recollision from different ends of a polar molecule. This phase difference has an impact on harmonics from aligned polar molecules, suppressing emission from the molecules parallel to the driving laser field while favoring the perpendicular ones. For oriented molecules, we measure the amplitude ratio of even to odd harmonics produced when intense light irradiates CO molecules and determine the degree of orientation and the phase difference of attosecond bursts using molecular frame ionization and recombination amplitudes. The sensitivity of the high harmonic spectrum to subtle phase differences in the emitted radiation makes it a detailed probe of polar molecules and will drive major advances in the theory of high harmonic generation.

Two-pulse orientation dynamics and high-harmonic spectroscopy of strongly-oriented molecules

“…ζ = 0.83. This improves the degree of field-free orientation compared to its first demonstration [39] by a factor of ∼15 and compared to previous high-harmonic studies of oriented molecules [40,65] by a factor of > 3.…”

Rotational dynamics of an asymmetric-top molecule in parallel electric and nonresonant laser fields

“…The availability of oriented molecules provides a wealth of intriguing applications in a variety of molecular sciences, such as in chemical reaction dynamics [1][2][3][4][5], photoelectron angular distributions [6][7][8], or high-order harmonic generation [9][10][11]. An oriented molecule is characterized by the confinement of the molecular fixed axes along the laboratory fixed axes and by its dipole moment pointing in a particular direction.…”

Bicircular High-Harmonic Spectroscopy Reveals Dynamical Symmetries of Atoms and Molecules

“…High-harmonic generation from a linearly polarized driver is sensitive to inversion symmetry, the breaking of which leads to emission of even harmonics [15,16] that characterize the time-dependent electronic asymmetry of the studied sample [14,17]. In this Letter, we generalize the sensitivity of HHS to rotational symmetries of atoms and molecules and their time-dependent breaking by introducing bicircular HHS (BHHS), driven by a circularly polarized fundamental field of frequency ω and its counterrotating second harmonic 2ω.…”