Archiv 2018

Raum: Seminar Room I, EG.076

Synchrotron Radiation from an Accelerating Light Pulse

MPSD Seminar
Synchrotron radiation is regularly generated at large-scale facilities where GeV electrons move along kilometer-long circular paths. Here, we use a metasurface to bend light and demonstrate synchrotron radiation produced by a sub-picosecond pulse, which moves along a circular arc of radius 100 μm inside a nonlinear crystal. The emitted radiation, in the THz frequency range, results from the nonlinear polarization induced by the pulse. The generation of synchrotron radiation from a pulse revolving continuously about a circular trajectory has profound implications for on-chip THz sources. We present the first step towards this realization. [mehr]

High-harmonic spectroscopy using bi-elliptical fields

MPSD Seminar
Over the recent years, high-harmonic generation has established itself as a promising spectroscopic technique. Notable examples include the tomographic imaging of molecular wave functions [1], the tracking of nuclear dynamics [2], and the reconstruction of the attosecond time-scale electron dynamics in molecules [3, 4].All these applications, however, have been limited to laser fields with linear polarization. High harmonic generation has only recently been extended to circularly-polarized drivers by utilizing a technique known as bi-circular high-harmonic generation (BHHG) [5,6,7]. In this talk, I will demonstrate the spectroscopic applications of this technique to the study of structure and dynamics of gas-phase atoms and molecules in a self-probing manner. I will start with an analysis of the helicity asymmetry of BHHG in noble-gas atoms and then proceed by illustrating how BHHG can be applied to study dynamical symmetry-breaking in a time-dependent manner in the context of rotational and vibrational molecular motion.Extension of high-harmonic generation to the regime of highly-elliptical fields opens up the way towards the study of chiral phenomena in high-harmonic generation. In this work, circular dichroism in the range of 3-8 % is observed on randomly oriented methyl oxirane (C3H6O) molecules in the gas phase. This chiral sensitivity is attributed to the sub-cycle chiral electron dynamics involving excited states of the cation that take place during the electron continuum propagation. Finally, I will present a study of time-dependent chirality based on following the temporal evolution of circular dichroism during the course of an ultrafast photodissociation reaction. [mehr]
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