Probing Polar Molecules with High Harmonic Spectroscopy

E. Frumker, N. Kajumba, J. B. Bertrand, H. J. Wörner, C. T. Hebeisen, P. Hockett, M. Spanner, S. Patchkovskii, G. G. Paulus, D. M. Villeneuve, A. Naumov, and P. B. Corkum

Phys. Rev. Lett. 109, 233904 – Published 4 December 2012; Erratum Phys. Rev. Lett. 109, 249902 (2012)

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.

Received 25 July 2012
Corrected 5 December 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.233904

Corrections

5 December 2012

Erratum

Publisher’s Note: Probing Polar Molecules with High Harmonic Spectroscopy [Phys. Rev. Lett. 109, 233904 (2012)]

E. Frumker, N. Kajumba, J. B. Bertrand, H. J. Wörner, C. T. Hebeisen, P. Hockett, M. Spanner, S. Patchkovskii, G. G. Paulus, D. M. Villeneuve, A. Naumov, and P. B. Corkum

Phys. Rev. Lett. 109, 249902 (2012)

Authors & Affiliations

E. Frumker^1,2,3,*, N. Kajumba¹, J. B. Bertrand¹, H. J. Wörner¹, C. T. Hebeisen¹, P. Hockett⁴, M. Spanner⁴, S. Patchkovskii⁴, G. G. Paulus³, D. M. Villeneuve¹, A. Naumov¹, and P. B. Corkum^1,†

¹Joint Attosecond Science Laboratory, University of Ottawa and National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada
²Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany
³Department of Physics, Texas A&M University, College Station, Texas 77843, USA
⁴Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada

^*eugene.frumker@mpq.mpg.de
^†paul.corkum@nrc.ca

High-Harmonic Spectroscopy of Oriented OCS Molecules: Emission of Even and Odd Harmonics

P. M. Kraus, A. Rupenyan, and H. J. Wörner

Phys. Rev. Lett. 109, 233903 (2012)

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Vol. 109, Iss. 23 — 7 December 2012

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Images

Figure 1
Spectral interference lies at the heart of high harmonic generation from oriented molecules. Every $1 / 2$ period of the fundamental intense infrared laser pulse (shown in red), an electron wave packet is detached from an oriented molecule, oscillates in the time-dependent electric field and recombines to create an attosecond burst of XUV light. An example of four such bursts of a train is shown in the figure. In our experiment, this attosecond pulse train is diffracted and imaged by a grating. The spectral interference of such a train results in the formation of even and odd harmonics. An experimental spectrum is shown in the figure.Reuse & Permissions
Figure 2
(a) The Dyson orbital for the most weakly bound valence electron of the isoelectronic pair, $N_{2}$ and CO. The color code represents a $π$ phase difference. The orientation is preserved in (b) and (c). (b) The total ionization yield as a function of the angle between the molecular axis and the electrical field calculated for a $1 / 2$ cycle of 800 nm with intensity $1.5 \times 10^{14} W / {cm}^{2}$ . (c) The amplitude (vertical axis) and phase (color code) of the transition moment as a function of angle and harmonic order (radial axis) for XUV light polarized along the molecular axis.Reuse & Permissions
Figure 3
Upper plot: Dotted green curve shows alignment of CO determined from a Coulomb explosion imaging measurement. The time-resolved high harmonic yields (19th harmonic), corresponding to the same rotational wave packet, are shown for CO (solid red curve) and $N_{2}$ (dashed blue curve) near the time of their first full revival (set at $t = 0$ ). Lower plot: An orientational wave packet in CO excited by the superposition of 800 and 400 nm light. Dotted green curve shows the orientation of CO measured by Coulomb explosion imaging. The red solid curve shows the time dependent signal for the 14th harmonic. Note that the even harmonic signal is maximum when the orientation is greatest.Reuse & Permissions
Figure 4
The high harmonic spectrum is shown at 8.85 fs, the time of maximum orientation. The intensity of all harmonics is presented in the top panel of the figure, showing in graphical form what is measured in the image below. The ratio of even to the average of the adjacent odd harmonics is shown in the upper bar graph. The lower bar graph plots the normalized difference $- R = (S_{a a} - S_{a}) / S_{b}$ . The figure inset shows the phase difference (in green, circle marks) for an electron departing from the -C- side and the -O- side of the molecule as determined by $e$ -polyscat simulations. The red (cross marks) curve is the measured spectral phase asymmetry of successive attosecond XUV (recollision electron) pulses (relative to the normally expected asymmetry). The blue (square marks) curve is the recolliding electron wave-packet spectral phase asymmetry.Reuse & Permissions

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