Adam Wyatt: ARIES

Adam from RAL (ex. Oxford) will present results from our ARIES collboration.

Nacho: DM: Searching for control mechanisms over plasma composition; two-pulse femtosecond ablation approach

Zolt: DM: How to "count the number" of electrons on a molecular orbital

One of the main goals of attosecond science is to see how the electrons are "behaving" in a molecule and to have a control over the behavior.

Two-color HHG may provide a way to achieve both of the above listed aims at the same time. In N2 the energy separation of the HOMO and HOMO-1 corresponds to 1.4eV. Removing an electron from HOMO by tunnel ionization leaves an electronic hole there. Subsequently, irradiating the target with a pump beam, one may start a Rabi kind of population transfer between HOMO and HOMO-1. Depending on the excursion time of the electrons the different harmonic orders may find the HOMO orbital populated differently.

We expect that due to the population evolution of the HOMO electronic state the spectrum of the emitted harmonics will be altered.

Felicity: JC: High Harmonic Spectroscopy of the Cooper Minimum in Molecules (click to see details)

The Cooper minimum (CM) has been studied using high harmonic generation solely in atoms. Here, we present detailed experimental and theoretical studies on the CM in molecules probed by high harmonic generation using a range of near-infrared light pulses from λ=1.3 to 1.8  μm. We demonstrate the CM to occur in CS2 and CCl4 at ∼42 and ∼40  eV, respectively, by comparing the high harmonic spectra with the known partial photoionization cross sections of different molecular orbitals, confirmed by theoretical calculations of harmonic spectra. We use CM to probe electron localization in Cl-containing molecules (CCl4, CH2Cl2, and trans-C2H2Cl2) and show that the position of the minimum is influenced by the molecular environment.
Download the paper here:
http://prl.aps.org/abstract/PRL/v110/i3/e033006
or here:
http://www.phys.ksu.edu/personal/atle/Papers/Minimum_HHG_prl13.pdf

NEW WEBSITE

To make it easier for me to add events and also easier for you I will now use a new website and a google calendar. You can link individual events and the whole calendar to your own calendar.

HERE it is: https://sites.google.com/site/iclcjournalclub/home

we are back here on the original...

Thoma: DM: The Water Project

I will present two new types of targets which could get implemented in the red dragon lab over the next few months. The novelty of these targets lie in the fact that they make the liquid phase of matter available in our lab.

The 1st project looks into using a thin liquid water sheet as the generation medium for high harmonics. Gravity driven aqueous thin film technology has been demonstrated at atmospheric pressure [1] but I believe that with adequate design considerations we should be able to move it inside the vacuum tin. "non perturbative" harmonic generation has been demonstrated converting a mid-IR laser to visible wavelengths [2].

The 2nd project will be looking at 100nm sized silicon nitride cells to hold water in the transient absorption beam-line. Once the targets exists, a range of experiments can be thought of: one of the 1st ones I would like to try would be the time resolved generation of H3O+ following the 2 to 4 photon ionisation of H2O by a 400nm field by looking at absorption by the 3rd IP of H3O+ around 32eV [3]. This has been theorised to happen in 10's of fs but to my knowledge has never been measured.

Our collaborators from epfl would be keen to look at some vibrational excitation induced changes [4] in the absorption spectrum to use alongside some photo-electron spectra data acquired at ral last year.

During this presentation I will discuss both the science behind these experiments and the mechanical designs we hope to use to surpass the technical difficulties associated with combining XUV radiation and liquid phase samples.

[1] Rev. Sci. Instrum. 74, 4958 (2003); doi: 10.1063/1.1614874

[2] Vol. 17, No. 23 / OPTICS EXPRESS 20959

[3] J. Am. Chem. Soc. 128, 3864 (2006)

[4] science 297, 587 (2002)

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