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. 2016 Dec 20:6:39295.
doi: 10.1038/srep39295.

Polarization shaping of high-order harmonics in laser-aligned molecules

E Skantzakis  1 , S Chatziathanasiou  1   2 , P A Carpeggiani  3 , G Sansone  4   5   3 , A Nayak  4 , D Gray  1 , P Tzallas  1   4 , D Charalambidis  1   2   4 , E Hertz  6 , O Faucher  4   6
Affiliations

Polarization shaping of high-order harmonics in laser-aligned molecules

E Skantzakis et al. Sci Rep. .

Abstract

The present work reports on the generation of short-pulse coherent extreme ultraviolet radiation of controlled polarization. The proposed strategy is based on high-order harmonics generated in pre-aligned molecules. Field-free molecular alignment produced by a short linearly-polarized infrared laser pulse is used to break the isotropy of a gas medium. Driving the aligned molecules by a circularly-polarized infrared pulse allows to transfer the anisotropy of the medium to the polarization of the generated harmonic light. The ellipticity of the latter is controlled by adjusting the angular distribution of the molecules at the time they interact with the driving pulse. Extreme ultraviolet radiation produced with high degree of ellipticity (close to circular) is demonstrated.

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Figures

Figure 1
Figure 1. Experimental setup for polarization shaping of high-harmonic radiations generated in transiently aligned molecules.
M: Mirrors; BS: Beam splitter; HWP: Half-wave plates; λ/4: Quarter-wave plate.
Figure 2
Figure 2
(a) Polarization analysis of the linearly-polarized harmonic field generated at 88.9 nm. Each data point represents an averaging over 10 laser shots. (b) The corresponding signal depicted in a polar plot. Experimental (numerical) data are shown with blue circles (red lines).
Figure 3
Figure 3. 9th harmonic versus delay between a linearly-polarized aligning and a circularly-polarized driving pulse.
Tr = 42.7 ps: full revival period of CO2.
Figure 4
Figure 4
(a) 9th harmonic intensity recorded for the horizontal and vertical orientation of the analyzer axis. The dotted vertical line indicates the delay at which the polarization analysis is conducted (see right panel). (b) Polarization analysis with the experimental (numerical) data depicted with blue circles (red line). The fitted ellipticity is ε = 0.14.
Figure 5
Figure 5
(a) Harmonic intensity recorded for the horizontal and vertical orientation of the analyzer axis. Harmonics generated with different polarizations states: (b) 9th harmonic (ε = 0.85), (c) 9th harmonic (ε = 0.8), and (d) 7th harmonic (ε = 0.74) (see text).
Figure 6
Figure 6. Generation of the 9th harmonic depicted in the multiphoton representation.
The molecules are aligned with a linearly-polarized pulse and the harmonic is generated by a left-handed circularly-polarized fundamental pulse (σ+) of frequency ω; (a) only the field driving the harmonic generation is applied; (b) the molecule is first aligned and then exposed to the fundamental driving pulse; (c) the same as (b) but with different intermediate transitions.
See this image and copyright information in PMC

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