JC: Misha: Radiation Generated by the Ultrafast Migration of a Positive Charge Following the Ionization of a Molecular System

Electronic many-body effects alone can be the driving force for an ultrafast migration of a positive charge created upon ionization of molecular systems. Here we show that this purely electronic phenomenon generates a characteristic IR radiation. The situation when the initial ionic wave packet is produced by a sudden removal of an electron is also studied. It is shown that in this case a much stronger UV emission is generated. This emission appears as an ultrafast response of the remaining electrons to the perturbation caused by the sudden ionization and as such is a universal phenomenon to be expected in every multielectron system.
http://prl.aps.org/abstract/PRL/v106/i5/e053001
What I want everyone to think about is:
- What is the role of the detached electron that they have completely neglected?
- Can this radiation be observed, and if yes, will it be coherent?
PPT slides to follow...#

DM: Luis: how to grow micro and nanostructures, with both, nanosecond and femtosecond laser pulses

(i) Laser irradiation of materials with laser pulses whose energy density is around the ablation limit, no matter whether they are femtosecond or nanosecond pulses, do produce microconical structures despite of the, most likely, different mechanisms involved. These structucture do have several interesting applications.
(ii) We will show how a metalic thin film of nanoparticles can be rearranged just by shining few laser pulses with a well defined intensity structure.
PPT slides to follow...

DM: Malte: Molecular structure dependence of recollision induced fragmentation in N2

After converting the VMI in the Red Dragon lab to an ion time-of-flight spectrometer, it is currently used to investigate those inelastic electron recollisions, which lead to fragmentation. Inelastic recollisions lead to electron-electron interactions in the outer shell of the molecule and investigating them is one of the objectives of attosecond science.
In the lab, we are trying to find out if the recollision induced fragmentation of N2 depends on the alignment of the molecule, or in other words if fragmentation is more probable if the electron hits the molecule parallel or perpendicular with respect to the bond.
I will give a detailed description of the required experimental steps to find an answer to that question and present a few intermediate results. I will try to raise a few questions about the setup and future plans to get input from the group.
Most of the experimental issues are mentioned in the following paper, written by a very familiar Irish man: http://pra.aps.org/abstract/PRA/v73/i4/e043401 Nevertheless, I will briefly discuss them during the meeting as well.
PPT slides to follow...

JC&DM: Tobi: Characterization of high intensity sub-4-fs laser pulses using spatially encoded spectral shearing interferometry

I'll try to give a mini-intro about ultrafast pulse characterisation and the SPIDER technique and discuss the latest attolab output

JC: Will: Higher-Order Kerr Terms Allow Ionization-Free Filamentation in Gases v2.0

follow up on the last Journal Club... http://www.opticsinfobase.org/abstract.cfm?URI=oe-17-16-13429
and http://www.opticsinfobase.org/abstract.cfm?URI=oe-18-3-3011
and: http://pre.aps.org/abstract/PRE/v74/i3/e036406

PDFs for the papers... PPT slides to follow...
 

DM: Leszek: Partial Covariance Mapping -- an experimental technique for FELs

* covariance mapping principle and its relation to coincidences [1,3]
* three- and higher-fold covariance [2]
* what is partial covariance and why is it useful?
* the noise from uncorrelated background (false coincidences)
* can partial covariance mapping be generalised to multi-fold correlations?
The introduction is going to be brief - really, the audience should be familiar with earlier work:

1. .Covariance Mapping: A Correlation Method Applied to Multiphoton Multiple Ionisation. L J Frasinski, K Codling and P A Hatherly Science 246 1029.1031 (1989)
2. .Multiphoton multiple ionisation of N2O probed by three-dimensional covariance mapping. L J Frasinski, P A Hatherly and K Codling Physics Letters A 156 227.232 (1991)
3. .Covariance mapping and triple coincidence techniques applied to multielectron dissociative ionization. L J Frasinski, A J Giles, P A Hatherly, J H Posthumus, M R Thompson and K Codling J. Electron Spectrosc. Relat. Phenom. 79 367.371 (1996)
PDFs for the papers as we don't have access to Physics Letters A... PPT slides to follow...

JC&DM: Henry Hutch: Molecular high harmonic generation in a two-color field

They carry out HHG in Methane and Xeon using two colours and show a suppression of the HHG signal in Methane in the presence of a .weak. 1500-1900 field from an OPA which is resonant with a vibration transition in Methane. This has quite a lot of cross over with work that has been done or is being carried out with the Red Dragon lab.
We experimentally investigate the high harmonic generation (HHG) from CH4 molecules and Xe atoms in a two-color field (using the 800nm laser and the tunable laser with the longer wavelength from 1500nm to 1900nm), and observe that the longer wavelength component can destructively suppress the HHG from CH4 molecules. By controlling the time delay between the two color laser pulses or tuning the laser intensity of the longer wavelength component, the suppressions of the HHG from CH4 molecules and the enhancements of the HHG from Xe atoms at the same laser condition are observed. The results indicate that the longer wavelength component around the molecular infrared absorption can suppress the molecular HHG process.
http://www.opticsinfobase.org/abstract.cfm?uri=oe-18-11-11664
PPT slides to follow...