(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...
Tuesday, 22 February 2011
Tuesday, 8 February 2011
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...
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...
Tuesday, 25 January 2011
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
Tuesday, 14 December 2010
JC: Will: Higher-Order Kerr Terms Allow Ionization-Free Filamentation in Gases v2.0
Tuesday, 7 December 2010
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...
* 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...
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.
http://www.opticsinfobase.org/abstract.cfm?uri=oe-18-11-11664
PPT slides to follow...
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...
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.
http://prl.aps.org/abstract/PRL/v104/i10/e103903
PPT slides and other material here
http://prl.aps.org/abstract/PRL/v104/i10/e103903
PPT slides and other material here
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