Jon L: JC: Probing Time-Dependent Molecular Dipoles on the Attosecond Time Scale

Photoinduced molecular processes start with the interaction of the instantaneous electric field of the incident light with the electronic degrees of freedom. This early attosecond electronic motion impacts the fate of the photoinduced reactions. We report the first observation of attosecond time scale electron dynamics in a series of small- and medium-sized neutral molecules (N2, CO2, and C2H4), monitoring time-dependent variations of the parent molecular ion yield in the ionization by an attosecond pulse, and thereby probing the time-dependent dipole induced by a moderately strong near-infrared laser field. This approach can be generalized to other molecular species and may be regarded as a first example of molecular attosecond Stark spectroscopy.

http://prl.aps.org/abstract/PRL/v111/i3/e033001

Thoma: JC: LIAD-fs scheme for studies of ultrafast laser interactions with gas phase biomolecules

Laser induced acoustic desorption (LIAD) has been used for the first time to study the parent ion production and fragmentation mechanisms of a biological molecule in an intense femtosecond (fs) laser field. The photoacoustic shock wave generated in the analyte substrate (thin Ta foil) has been simulated using the hydrodynamic HYADES code, and the full LIAD process has been experimentally characterised as a function of the desorption UV-laser pulse parameters. Observed neutral plumes of densities >109 cm−3 which are free from solvent or matrix contamination demonstrate the suitability and potential of the source for studying ultrafast dynamics in the gas phase using fs laser pulses. Results obtained with phenylalanine show that through manipulation of fundamental femtosecond laser parameters (such as pulse length, intensity and wavelength), energy deposition within the molecule can be controlled to allow enhancement of parent ion production or generation of characteristic fragmentation patterns. In particular by reducing the pulse length to a timescale equivalent to the fastest vibrational periods in the molecule, we demonstrate how fragmentation of the molecule can be minimised whilst maintaining a high ionisation efficiency.

paper: http://pubs.rsc.org/en/Content/ArticleLanding/2012/CP/c2cp23840c#!divAbstract

Simon: JC: Timing analysis of infrared-driven high-order harmonic generation with above-ionization attosecond pulses

We theoretically study infrared (IR)-driven high-order harmonic generation (HHG) assisted by attosecond pulses with a central energy above the atomic ionization threshold. We provide a clear physical picture for controlling HHG using the time delay between the attosecond pulses and the IR laser reported by Faria et al. [Phys. Rev. A 74, 053416 (2006)]. This physical picture also indicates that the combined attosecond pulses and IR laser can help resolve the dynamics of ionized electrons from time-dependent harmonic spectra. We present the quantum effect on HHG as an example. While leaving parent ions, ionized electrons can still emit harmonics in the semi-classically forbidden situation. The two-color excitation provides a practical method to observe the quantum effect experimentally. Furthermore, in our work, attosecond pulses and an IR field are considered with a realistic pulse shape, which shows a quantitatively important effect in controlling harmonic spectra. Accordingly, a guide to optimize the control capability for HHG is presented, and a method to determine the IR carrier-envelope phase based on the pulse-shape effect on the HHG is also proposed.
http://www.opticsinfobase.org/josab/abstract.cfm?uri=josab-30-5-1294

Davide

Peter: JC: Observation of high-order harmonic generation in a bulk crystal

http://www.nature.com/nphys/journal/v7/n2/full/nphys1847.html

Thoma: JC: Sub-cycle Oscillations in Virtual States Brought to Light

http://www.nature.com/srep/2013/130122/srep01105/full/srep01105.html?WT.ec_id=SREP-20130129

Johannes Floß: DM: Quantum resonance, Anderson localisation and selective rotational excitation in periodically kicked molecules

guest speaker: Johannes Floß, Department of Chemical Physics, Weizmann Institute of Science, Israel

The periodically kicked rotor has attracted much attention in the recent decades. In the classical regime the kicked rotor can exhibit truly chaotic motion, whereas in the quantum mechanical analogue, this chaotic motion is suppressed by Anderson-like localisation of the wave function in momentum space [1]. On the other hand, when the kicking period is equal to the rotational revival time, the kicked quantum rotor exhibits quantum resonance, an effect which leads to a linear increase of the angular momentum with the number of kicks [2]. Until today these phenomena were observed experimentally mainly in an atom optics analogue of a kicked rotor [3].

In this talk, I will provide an introduction to the two phenomena of quantum resonance and Anderson localisation in periodically kicked rotors. Then I will show how standard laser techniques used for molecular alignment provide a new way for observing these phenomena in a real rotor system, a diatomic molecule [4, 5]. I will also show that these phenomena provide a new toolbox for selective laser manipulations in molecular mixtures.

[1] S. Fishman, D. R. Grempel, and R. E. Prange, Phys. Rev. Lett. 49, 509 (1982).
[2] F. M. Izrailev and D. L. Shepelyanskii, Theor. Math. Phys. 43, 553 (1980).
[3] F. L. Moore, J. C. Robinson, C. Bharucha, B. Sundaraman, and M. G. Raizen, Phys. Rev.
Lett. 75, 4598 (1995).
[4] J. Floß and Ilya Sh. Averbukh, Phys. Rev. A 86, 021401 (R) (2012).
[5] J. Floß, S. Fishman, and Ilya Sh. Averbukh, arXiv 1305.5995 (2013).