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

Abstract

Abstract. We present the detailed analysis of a new two-pulse orientation scheme that achieves macroscopic field-free orientation at the high particle densities required for attosecond and high-harmonic spectroscopies [P. M. Kraus et al., arxiv:1311.3923]. Carbon monoxide (CO) molecules are oriented by combining a one-color and a delayed two-color non-resonant femtosecond laser pulses. High-harmonic generation is used to probe the oriented wave-packet dynamics and reveals that a very high degree of orientation (N up /N total = 0.82) is achieved. We further extend this approach to orienting carbonyl sulfide (OCS) molecules. We show that the present two-pulse scheme selectively enhances orientation created by the hyperpolarizability interaction whereas the ionization-depletion mechanism plays no role. We further control and optimize orientation through the delay between the one-and two-color pump pulses. Finally, we demonstrate a complementary encoding of electronic structure features, such as shape resonances, in the even-and odd-harmonic spectrum. The achieved progress makes two-pulse field-free orientation an attractive tool for a broad class of time-resolved measurements.

Two-Pulse Field-Free Orientation Reveals Anisotropy of Molecular Shape Resonance

“…[29,30] using the hyperpolarizability interaction and additionally incorporate the ionization-depletion mechanism [28] with details given in Ref. [35]. (b) Highharmonic spectrum of CO oriented by the one-pulse scheme recorded under conditions otherwise identical to the upper spectrum.…”

Perspectives of Attosecond Spectroscopy for the Understanding of Fundamental Electron Correlations

“…[69] Similar electronic structure effects have been investigated and demonstrated for molecular Cooper minima [73,74,76] and shape resonances. [73,[75][76][77][78] Second, the unique mapping between electron trajectories and emitted frequencies serves as a tool for selfprobing of molecular dynamics. First demonstrated for monitoring the proton dynamics in H + 2 , this idea was extended to study the interference of high harmonics emitted from different cationic states in CO 2 [82,110,111] and N 2 .…”

“…Attosecond lighthouse experiments [132][133][134][135][136][137][138] with oriented molecules could give direct access to amplitude and phase asymmetries for the different recollision sides of oriented molecules. Two-color HHG experiments [58][59][60][139][140][141][142] in combination with molecular orientation [77,78,99,[116][117][118] can provide a new observable for the reconstruction. The polarization of the second color can be chosen to be perpendicular to that of the first color to solely manipulate the electron trajectories [59,140] and not the tunneling process.…”

“…The plane-wave approximation was, however, questioned, when signatures known from photoionization cross sections were identified in HHG spectra, [68][69][70] which revealed the importance of a correct description of the photoionization continuum beyond the plane-wave approximation. Examples include the electronic structure minimum in argon [69] and the giant resonance in xenon [71,72], both of which are discussed in this review, as well as further studies of Cooper minima [73,74] and shape resonances [73,[75][76][77][78] in molecules.…”

“…A convenient basis for the singleelectron continua is a partial-wave expansion, which we used previously to analyze the photorecombination step in carbon monoxide. [77,78] Typically, only a few partial waves with different angular momenta have a major contribution to the total recombination matrix element due to symmetry. As an example, photorecombination to a pure atomic p-orbital will result in a continuum that can be described by s-and d-waves (referring to angular momenta of = 0 and = 2), as in the case of HHG in argon (Ref.…”