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K: Fachverband Kurzzeitphysik

K 7: Poster

K 7.5: Poster

Mittwoch, 19. März 2014, 16:30–18:30, SPA Foyer

Polarization Dependence of Laser Dressed States in Helium — •Johan Hummert¹, Maurizio Reduzzi¹, Fabio Frasetto², Antoine Dubrouil¹, Chengyong Feng¹, Francesca Calegari¹, Mauro Nisoli¹, Luca Poletto², Kenneth Schafer³, Mette Gaarde³, and Giuseppe Sansone¹ — ¹Politecnico di Milano, Italy — ²Universita degli Studi di Padova, Italy — ³Louisiana State University, USA

Measuring the spectrally resolved absorption of atoms grants direct insight into their electronic structure. Paired with the high time resolution obtained with attosecond pulses this allows us to investigate the dynamics of bound electrons in a strong laser field.

Here we present transient absorption measurements in helium with attosecond time resolution. The experimental setup uses a few cycle near infrared pulse with variable polarization as a pump and an attosecond extreme ultraviolet pulse as a probe. The attosecond pulses are generated by few cycle IR pulses using high harmonic generation in combination with the polarization gating technique.

Apart from other strong-field effects light-induced features corresponding to so-called laser dressed states are observed. It is found that the absorption cross section of these laser dressed states depends strongly on the relative polarization of the pulses. We show that Floquet theory can be used to understand this behaviour. A simple analytic approach to the time-independent Floquet Hamiltonian method proves sufficient to reproduce the observed polarization dependence of dressed state absorption completely.