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Tuesday, 23 November 2010

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.
PPT slides to follow...

Tuesday, 16 November 2010

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.
PPT slides and other material here

Tuesday, 9 November 2010

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

Tuesday, 2 November 2010

DM: Amelle: Molecular QPI

I will discuss our recent result on molecular internal dynamics studied by quantum path interferences in high order harmonic. Upon a certain number a available technique we are looking in providing one that is self-referenced and will allowed to access information on the nuclear and electron dynamics of the cation created in the time scale of the HHG process.

Tuesday, 26 October 2010

JC: Sebastien: Mapping Molecular Orbital Symmetriy on High-Order Harmonic Generation Spectrum Using Two-Color Laser Fields

We have measured high-order harmonic generation spectra of D2, N2, and CO2 by mixing orthogonally polarized 800 and 400 nm laser fields. The intensity of the high-harmonic spectrum is modulated as we change the relative phase of the two pulses. For randomly orientated molecules, the phase of the intensity modulation depends on the symmetry of the molecular orbitals from which the high harmonics are emitted. This allows us to identify the symmetry of any orbital that contributes to high-harmonic generation, even without aligning the molecule. Our approach can be a route to imaging dynamical changes in three-dimensional molecular orbitals on a time scale as short as a few hundred attoseconds.

Tuesday, 19 October 2010

DM: Chris Arrell: Thesis and Surface Science Experiments Outlook

I will present measurements from the surface science apparatus and discuss the next steps for the project. Measurements have shown evidence of localised plasmonic enhancement from silver and 'hot-electron' temporal dynamics on an Au surface

Tuesday, 12 October 2010

JC: Richard: Inconsistencies between two attosecond pulse metrology methods: A comparative study

The two basic approaches underlying most of the metrology of attosecond pulse trains are compared in the spectral region ~14-24 eV, that is, the second-order intensity volume autocorrelation and the resolution of attosecond beating by interference of two photon transitions (RABITT). They give rather dissimilar pulse durations. It is concluded that for the present experimental conditions RABITT may underestimate the duration under measurement, due to variations of the driving intensity, but in conjunction with theory allows an estimation of the relative contributions of two different electron trajectories to the extreme-ultraviolet (XUV) radiation.
PPT slides...

Tuesday, 5 October 2010

DM: Ryan: Tunneling discussion which directly measures tunneling in a strong field. I may also speak about: which claims to have measured tunneling time I will speak about that and offer a `tutorial' of sorts on tunneling covering the main features of tunneling and the basic theories behind that and the 3-step model. It will be a discussion of the paper coupled with a short lesson on the stuff that I am most often asked about by dirty experimentalists.
If there are specific things people want to know send Ryan an email.

Tuesday, 21 September 2010

DM: Thomas: SMURF

after the promising results of the 1st SMURF experiment ( ) we are going to attempt to push the technique further. The 1st experiment having been carried out in under 2 days with no forward planning what so ever, so this is our chance to attempt to do it properly. during this presentation i will quickly run through what other people have done in the recent past in terms of water-window xray generation, what the smurf is likely to bring extra, and ask for people's inputs on a variety of still undecided parameters and techniques.
to make the discussion more lively tobi is going to buy us loads of scrumpy cider!