Dependence of Laser-Driven Coherent Synchrotron Emission Efficiency on Pulse Ellipticity and Implications for Polarization Gating

M. Yeung, B. Dromey, S. Cousens, T. Dzelzainis, D. Kiefer, J. Schreiber, J. H. Bin, W. Ma, C. Kreuzer, J. Meyer-ter-Vehn, M. J. V. Streeter, P. S. Foster, S. Rykovanov, and M. Zepf

Phys. Rev. Lett. 112, 123902 – Published 26 March 2014

Abstract

The polarization dependence of laser-driven coherent synchrotron emission transmitted through thin foils is investigated experimentally. The harmonic generation process is seen to be almost completely suppressed for circular polarization opening up the possibility of producing isolated attosecond pulses via polarization gating. Particle-in-cell simulations suggest that current laser pulses are capable of generating isolated attosecond pulses with high pulse energies.

Received 8 December 2013

DOI:https://doi.org/10.1103/PhysRevLett.112.123902

Authors & Affiliations

M. Yeung^1,*, B. Dromey^1,†, S. Cousens¹, T. Dzelzainis¹, D. Kiefer^2,5, J. Schreiber^2,5, J. H. Bin^2,5, W. Ma^2,5, C. Kreuzer⁵, J. Meyer-ter-Vehn², M. J. V. Streeter³, P. S. Foster⁴, S. Rykovanov^5,‡, and M. Zepf^1,6

¹Department of Physics and Astronomy, Queen’s University Belfast, Belfast BT7 1NN, United Kingdom
²Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, D-85748 Garching, Germany
³Blackett Laboratory, Imperial College London, London SW7 2BZ, United Kingdom
⁴Central Laser Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom
⁵Fakultät für Physik, Ludwig-Maximilians-Universität München, D-85748 Garching, Germany
⁶Helmholtz-Institut Jena, Fröbelstieg 3, 07743 Jena, Germany

^*Present address: Helmholtz-Institut Jena, Fröbelstieg 3, 07743 Jena, Germany.
^†b.dromey@qub.ac.uk
^‡Present address: Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.

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Vol. 112, Iss. 12 — 28 March 2014

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Images

Figure 1
(a) Sketch of the experimental setup and raw data showing the effect of pulse ellipticity. The laser is focused by an $f / 2$ off-axis parabola onto the ultrathin foil target. The transmitted XUV light is analyzed by passing it through a narrow slit or pinhole followed by a $1000 lines / mm$ transmission grating which spectrally disperses the light onto an MCP detector. (b) XUV spectra—the shaded areas below the curves show the difference in signal for the linear driver (upper solid curve) and a circular driver (lower dotted curve). (c) Ellipticity scaling—the raw MCP images are shown for each ellipticity setting as indicated by the adjacent electric field vector plot. The lower three images indicated by an asterisk have been shown at a 5 times reduced color-map scale.
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Figure 2
Comparison of simulation and experiment. Harmonic efficiency for orders 7–15 as obtained from picwig simulations (circles) is plotted alongside the integrated harmonic signal for the same orders but for the experimental data (crosses). The dash-dotted line shows the detector noise floor as obtained from a shot without a target. Data points are single shots and the errors are due to some uncertainty in the exact values used for correction of the nonharmonic background signal, while the laser energy variation was $\approx 4 %$ for this shot set.
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Figure 3
Results of picwig simulations of polarization gating. The intensity is plotted for the constructive pulse pair (dashed) and destructive pulse pair (solid) in (a) for the IPG method. Note that these two pulse pairs are orthogonally polarized and are out of phase by $π / 2$ . The intensities of the two opposite-handed circular pulses for the birefringent plates method are plotted in (b). In both cases the ellipticity of the composite pulse is also plotted (dotted). The electron densities from picwig simulations, plotted against time and position, are shown (dark areas are low density while bright regions are high) for the cases of (c) an ungated 11-cycle FWHM (full width at half maximum) Gaussian pulse (similar to the optimum capability of Astra Gemini), (d) an ungated 2-cycle pulse, (e) an 11-cycle pulse gated by IPG, and (f) a 2-cycle pulse gated by the plate method. The harmonic field intensity frequency filtered to orders above the 20th is also plotted over the density map. For the gated pulses the transmitted XUV radiation is restricted to the period of linear polarization.
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Figure 4
Direct comparison of transmitted gated and ungated XUV pulses. (a) Plot of the normalized instantaneous intensity against time for the 2-cycle driver case for gated (solid) and ungated (dotted) pulses as obtained from picwig simulations. The intensity is determined by the square of the transmitted electric field after frequency filtering out harmonic orders below the 20th. Also shown is a Gaussian fit (dashed) with a FWHM of 77 as to approximate the envelope of the isolated pulse. (b) Plot for the 11-cycle pulse showing the gated (solid) and ungated (dotted) intensities. A Gaussian fit (dashed) is also shown that yields a FWHM duration of 370 as.
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