Recent Physics and Future Developments P.A. Hatherly J.J. Thomson Physical Laboratory University of Reading Whiteknights Reading RG6 6AF
Sources used by the Reading Group I Like SR • Major International Facilities • SRS, Daresbury, UK • Beamline MPW6.1 PHOENIX • MAX II, Lund, Sweden • Beamline I411 • In-house helium lamp • 20 and 40 eV photons • Other energies available using Ne, Ar, Kr, Xe
Physics Programmes • Inner shell ionisation and excitation of molecules • Carried out at DL and MAX • High Resolution Studies of OCS at S 2p and C 1s • Absolute Cross Section Measurements • Recent Final Year Undergraduate Project • Measurement of the absolute absorption cross-section of SF5CF3 • Resolving a conflict in values in the literature • Future plans to measure cross sections to allow SR data to be placed on an absolute scale
OCS Threshold Electron Studies • At the SRS, Daresbury • S 2p and C 1s excitation of OCS • Threshold electron and ion yield spectra • Fragmentation studies • Coincidence studies between threshold electrons and ions
OCS – S 2p Fragments OCS2+ C+ CO+f S+f CO+b O+ S+b
OCS – C 1s Fragments C+ CO+f S+f OCS2+ CO+b S+b O+
OCS Auger Studies • At MAX II, Sweden • S 2p excitation and Auger spectra • Fragmentation associated with given Auger channels • Coincidence studies between Auger electrons and ions
OCS – S 2p Fragments OCS2+ S I S+ S II OCS2+
Absorption Cross Sections • Absorption Cross Section of SF5CF3 measured • Disagreement of a factor of 2 between recently reported values at 10.2 eV (H Lyman a) • Final Year Undergraduate Project • Andrew Flaxman • Measured at He I (21.2 eV) and Ne I (16.7 eV, doublet)
Future Developments • Recent EPSRC grants to develop attosecond laser technology • Consortium including Reading (Leszek Frasinski), Oxford, Imperial College and Rutherford • Why talk about this at a SR meeting?
Attosecond Pulses • Aim of project to generate pulses of the order of 100 as long • Cannot be “optical” wavelengths (period ~ 2 fs) • Need VUV/SXR (eg, ~20 eV, period ~ 200 as) • Hence, need SR optics technology to handle the pulses
Attosecond Pulses • How to measure the pulse length? • With fs pulses, can use frequency doubling and autocorrelation techniques • With as pulses, need new techniques
…each generate an identical photoelectron spectrum Two delayed as x-ray pulse replicas incident on a gas target… Electron Energy An Application of PES!
…result – interference fringes in the PE spectrum… Now add slower, fs, pulse… Electron Energy An Application of PES! …energy levels shifted with time… …photoelectrons due to each as pulse shifted in energy… …Details of fringes gives as pulse spectrum and phase information – hence can reconstruct the pulse! (Quéré et al, PRL 90, 7 (21st Feb 2003))
Attosecond Lasers • Excellent examples of spin-off technology • VUV and SXR optics well understood in SR • Now being applied in a new area • PES developed as a tool for probing fundamental atomic and molecular properties • Now applied as a tool in it’s own right for a specific technological application • Note this under “Beneficiaries” etc. on your next EPSRC application!
Other Developments • Strong possibility of developing a fs laser laboratory at Reading • SRIF funding • High-harmonic generation systems for fs scale time resolved VUV work • Ongoing progress of 4GLS • Exciting possibilities of non-linear VUV phenomena
With Thanks: • Dr Marek Stankiewicz and Dr Jaume Rius i Riu • SR experiments at Daresbury and MAXlab • Mr Andy Flaxman • Undergraduate Project Student – Cross section data • Dr Leszek Frasinski • Atto- and femtosecond laser development