Daniel: DM: Experimental methods for time-resolved measurements of molecular electron dynamics

In the ‘attosecond lab’ we can now generate synchronised attosecond pulses at 20eV and 90eV, which we hope to use to make time resolved measurements of ultrafast electronic processes in atoms and molecules, such as charge migration. In conjunction, a new electron-ion particle detector has been installed (the ‘VMI-TOF’) in order to be able to get as much information as possible from the probe step in a ‘pump-probe’ measurement. I will try to give a brief overview of the theory of charge migration (from a non-theorist stand point!) and the challenges of making attosecond pump - attosecond probe measurements. I will then discuss the experimental implementation of spLEAD (single photon Laser Enabled Auger Decay) , a scheme to measure electron dynamics in the glycine molecule, and the operation of the VMI-TOF, with a view to informing future experiments .

Christian: JC: Efficient generation of below-threshold harmonics for high-fidelity multi- photon physics in the VUV spectral range

We demonstrate the generation of microjoule level, sub-20-fs, Ti:Sa fifth-harmonic pulses utilizing a loose-focusing geometry in a long Ar gas cell. The VUV pulses centered at 161.8 nm reach pulse energies of 1.1 μJ per pulse, while the corresponding pulse duration is measured with a second-order, fringe-resolved autocorrelation scheme to be 18±1  fs . Nonresonant, two-photon ionization of Kr and three-photon ionization of Ne verify the fifth-harmonic pulse high-intensity content and indicate the feasibility of multi-photon VUV pump-VUV probe studies of ultrafast atomic and molecular dynamics.

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-40-8-1675

Felicity: JC: Attosecond Hole Migration in Benzene Molecule Surviving Nuclear Motion

Hole migration is a fascinating process driven by electron correlation, in which purely electronic dynamics occur on a very short time scale in complex ionized molecules, prior to the onset of nuclear motion. However, it is expected that due to coupling to the nuclear dynamics, these oscillations will be rapidly damped and smeared out, which makes experimental observation of the hole migration process rather difficult. In this Letter, we demonstrate that the instantaneous ionization of benzene molecules initiates an ultrafast hole migration characterized by a periodic breathing of the hole density between the carbon ring and surrounding hydrogen atoms on a subfemtosecond time scale. We show that these oscillations survive the dephasing introduced by the nuclear motion for a long enough time to allow their observation. We argue that this offers an ideal benchmark for studying the influence of hole migration on molecular reactivity.

http://pubs.acs.org/doi/abs/10.1021/jz502493j

DM: Laser consortium LCLS subteam: Overview of our latest LCLS experiment: beamtime progress and results

Most of the members of the laser consortium already had a good idea of our aim for the LCLS experiment. However, experiments don't always go as expected, specially when they are done at facilities with a short pre-allocated beamtime, and the final results can be quite different from the original aim. In this journal club, we will show the progress of our latest experiment at LCLS shift by shift, and how the original plan had to be modified on the fly to to adapt to the different circumstances and issues we were presented with. The talk will include an overview of practical aspects, as how we calibrated the different devices within the beamtime, and will give a very quick overview of the potentially most relevant results, still open for discussion and interpretation.

Allan: JC: Generation of bright isolated attosecond soft X-ray pulses driven by multicycle midinfrared lasers

Generation of bright isolated attosecond soft X-ray pulses driven by multicycle midinfrared lasers
http://www.pnas.org/content/111/23/E2361

Christian: JC: Generation of intense supercontinuum in condensed media

Destructive nonlinear processes have limited the useful input power to a few megawatts for supercontinuum generation in bulk material. Consequently, reliable high-power, high-pulse-energy supercontinuum in condensed media has not been realized. Here, we describe an intense femtosecond supercontinuum generated in a solid medium with pulse energy and mode quality that approach those generated in the gas phase while preserving the advantages of a condensed medium of being compact, simple to operate, and highly reproducible. This is achieved by strategically placing several thin solid plates at or near the focused waist of a high-power laser pulse. The thickness of each plate is such that the optical pulse exits the plate before undesirable effects begin to take hold of the pulse. With this approach, we have obtained pulses that have an octave-spanning spectrum that covers from 450 to 980 nm at the −20  dB intensity level while converting as much as 54% of the input pulse energy to the continuum. The highest pulse energy obtained to date is 76 μJ, nearly two orders of magnitude greater than previously reported values. The transverse mode of the pulse has a M2 of 1.25. Frequency-resolved optical grating and spectral interferometric measurements indicate that the pulse is phase coherent and could be compressed to a few femtoseconds. Furthermore, the multiple-plates approach is shown to be extremely flexible and versatile. It is applicable for a broad range of input powers and materials. The generated continuum is stable and robust. Thus, multiple-plate generated femtosecond continuum could be a promising new light source in ultrafast science and extreme nonlinear optics applications.

http://www.opticsinfobase.org/optica/abstract.cfm?uri=optica-1-6-400

Konstantin: DM: Probing controlled dynamics

In this week's Journal Club I will discuss a proposed scheme to use the interference between short and long trajectories in HHG, so called Quantum Path Interference (QPI), to probe sub-femtosecond hole dynamics. The TDSE for a model H2 molecule in an intense IR field and a weaker UV field (resonant with the ionic transition between HOMO and HOMO-2) is solved numerically (idea and calculations by Suren Sukiasyan et al.). The population transfer driven by the resonant UV field changes the recombination probabilities of the short and long trajectories, leading to a change in QPI contrast. I will then discuss how we plan to implement this and similar experiments in the lab.