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...

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

We show that higher-order nonlinear indices (n4, n6, n8, n10) provide the main defocusing contribution to self-channeling of ultrashort laser pulses in air and argon at 800 nm, in contrast with the previously accepted mechanism of filamentation where plasma was considered as the dominant defocusing process. Their consideration allows us to reproduce experimentally observed intensities and plasma densities in self-guided filaments.
http://prl.aps.org/abstract/PRL/v104/i10/e103903
PPT slides and other material here

DM: Rashid: High-order Harmonic Generation of Laser Radiation in Plasmas: Recent Achievements and Perspectives

Resent research on high-order harmonic generation in laser-produced plasmas is reviewed. We analyze the conditions for the generation of harmonics (up to the 101st order, . ~ 7.9 nm) in the propagation of laser radiation through a weakly-ionized plasma prepared by irradiating the surfaces of different targets with a laser prepulse. First experiments on attosecond pulse generation from plasma plumes are presented. We discuss the findings of investigations into the resonance intensity enhancement of individual harmonics in a number of plasma formations, which have demonstrated a substantial increase in the conversion efficiency in the plateau region of the harmonic distribution (in particular, of the 13th harmonic in indium plasmas with the efficiency 10-4). We review the results of investigations of harmonic generation in nanoparticle-containing plasmas (metallic clusters, fullerenes, nanotubes). Different techniques for increasing the intensity and order of the generated harmonics are discussed. Future perspectives are analyzed as well. Among them are: (a) high-power harmonics from nanoclusters at 1 kHz pulse repetition rates, (b) few-cycle pump-induced harmonics, (c) molecular orientation in plasma plumes, (d) attosecond experiments, (e) plasma manipulations, (e) carbon-containing plasma: perspectives of application for plasma HHG, (f) long-wavelength femtosecond pump.

PPT slides and other material here