Chair: Stephen R. Leone, University of California, Berkeley, USA

  • Oren Cohen
  • Benoit Mahieu
  • Baptiste Fabre
  • Francois Mauger
  • Vincent Gruson

#39, 8:30 – 9:00 Generation of bright high-order harmonics with tunable polarization:Towards helically-polarized attosecond pulses, A. FLEISCHER, O. KFIR, T. DISKIN, P. SIDORENKO, E. BORDO, O. COHEN, P. GRYCHTOL, E. TURGUT, R. KNUT, D. ZUSIN, D. POPMINTCHEV, T. POPMINTCHEV, H. NEMBACH, J. SHAW, H. KAPTEYN AND M. MURNANE, Generation and application of bright phase-matched high-order harmonic with fully tunable polarization – from linear through elliptic to circular – are demonstrated experimentally. An accessible path towards generation of helically polarized attosecond pulses is presented.

#40, 9:00 – 9:15 Control of the ellipticity of high harmonics generated in a two-colour scheme, B. MAHIEU, G. LAMBERT, G. DE NINNO, D. GAUTHIER, C. SPEZZANI, A. ANDREEV, S. STREMOUKHOV, M. FAJARDO, C. P. HAURI, P. SALIÈRES, V. MALKA, B. VODUNGBO AND P. ZEITOUN, We study the control of the ellipticity of high harmonics generated in gas, driven by a two-colour laser field. Our pioneer work demonstrated the possibility to generate elliptically-polarized harmonics using linearly polarized driving fields [1]. Exploiting a Mach-Zehnder configuration, we go here a step further, mainly by changing the crossing angle of the driving fields’ linear polarizations. For values higher than 45°, a significant ellipticity (around 50%) is obtained for both odd and even harmonics. Furthermore, we show the possibility to modify the polarization axis of the individual harmonics. These measurements allow envisaging a full polarization control of harmonics and a better understanding of the generation process.

#41, 9:15 – 9:30 Towards Attosecond XUV Circular Dichroism, A. FERRÉ, C. HANDSCHIN, M. DUMERGUE, F. BURGY, A. COMBY, D. DESCAMPS, B. FABRE, G.A. GARCIA, R. GÉNEAUX, L. MERCERON, E. MÉVEL, L. NAHON, S. PETIT, B. PONS, D. STAEDTER, S. WEBER, T. RUCHON, V. BLANCHET AND Y. MAIRESSE, XUV circular dichroism is based on the asymmetric response of a target interacting with chiral light. Due to its differential character, this technique is a very sensitive and powerful tool to study structural properties of matter, from the photoionization of chiral systems to the magnetic properties of solids. However, extension of this technique, on synchrotron or free electron lasers, to dynamical studies is not straightforward. We present here a table-top and competitive alternative source based on high harmonic generation which delivers quasi-circular pulses in the extreme ultraviolet range.

#42, 9:30 – 9:45 High Harmonic Generation and Polarization: Angular Momentum Conservation vs Discrete Time-Dependent Symmetries, F. MAUGER, A.D. BANDRAUK AND T. UZER, We discuss the place of angular momentum conservation in theoretical and numerical models for high harmonic generation (HHG). Recent experimental work [A. Fleischer et al., Nature Photonics 8, 543 (2014)] has shown conflicting results regarding the conservation of the (photon) angular momentum in HHG. We show that simulations using classical fields do not conserve angular momentum and that the properties of HHG spectra are actually due to more general discrete time-dependent symmetries that apply equally well for atoms and molecules and we propose a configuration to test for the accuracy of simulations compared to selection rule predictions.

#43, 9:45 – 10:00 Depolarization in High Harmonic Generation, KEVIN VEYRINAS, VINCENT GRUSON, S. J. WEBER, L. BARREAU, T. RUCHON, J.C. HOUVER, B. CARRÉ, R.R. LUCCHESE, D. DOWEK AND P. SALIÈRES, We perform the first complete characterization of high harmonic polarization state including helicity and degree of polarization using molecular polarimetry, based on the analysis of the Molecular Frame Photoelectron Angular Distribution (MFPAD) in molecular dissociative photoionization. We study the elliptical XUV emission produced using three types of symmetry breaking: SF6 molecules irradiated by elliptically polarized laser, Argon atoms irradiated by counterrotating bichromatic fields, and N2 molecules aligned with respect to a linear driving field. Our results are compared to the incomplete optical polarimetry measurements performed up to now, revealing, e.g., in N2 , a much smaller ellipticity and significant depolarization.