Laser-Plasma Interactions and Femtosecond
X-ray Diffraction
The heart of the work of the research group is in laser-plasma
interactions. High power, terawatt lasers, provide the opportunity to create matter at
densities and temperatures similar to those found in the interiors of stars. It is a
field of study that is relevant to several other areas of physics, and also offers
the prospect of novel energy sources via inertial confinement fusion. I work closely
with Dr Simon Hooker and Professor Steven Rose, and together we form the Oxford Centre for
Ultrafast X-ray Physics. This area of research encompasses fusion, X-ray lasers, femtsecond X-ray
production and use, and the application of laser-plasmas to problems in astrophysics.
Laser-plasma sources, owing to their high temperature, are copious sources
of ultrashort hard X-rays. Indeed, pulse lengths as short as 300 fsec can be
produced. Similar pulse lengths can be achieved using streak camera technology in
combination with third-generation synchrotron sources, whilst the fourth generation X-ray
free electron laser sources currently being developed should deliver pulse lengths down to a few
femtoseconds. The group has an interest in developing and using these sources to probe matter on
ultrashort timescales. Most pump probe techniques take place in the optical regime, and can only
resolve features down to the wavelength of optical light. In contrast, X-rays can provide
time-resolved information on the evolution of material response at the Angstrom level. In particular,
femtosecond X-ray diffraction is a burgeoning area of activity where the group is very active in both
experiment and theory. We have developed simulations of diffraction on femtosecond and picosecond
time-scales from laser-irradiated crystals, showing how the presence of phonons can be
observed via X-rays directly in the temporal domain. We are also interested in using such sources to
investigate how matter deforms when subject to shock compression, and the ultimate timescales for
elastic-plastic flow and polymorphic phase transitions. With ultrashort X-ray pulses, the time-dependent
wavefields of the X-rays need to be calculated as the crystal is perturbed, and we have developed a
general 'Takagi-Taupin' equation to model these interactions.
Laser-produced plasmas are also of relevance to several areas of
astrophysics - the densities and temperatures produced in the plasmas are similar to those in certain astrophysical
environments. Such plasmas can also 'mimic' key astrophysical phenomena, providing us with a test bed for astrophysical
models. In particular we are studying how line radiation escapes from rapidly expanding media, a phenomenon of
importance to supernova explosions.
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Recent
Publications
Thomson scattering measurements of heat flow in a laser-produced plasma
J. Hawreliak, D.M. Chambers, S.H.Glenzer, A. Gouveia, R.J. Kingham, R.S.
Marjoribanks, P.A. Pinto, O. Renner, P. Soundhauss, S. Topping, E. Wolfrum,
P.E.Young, J.S. Wark,
J. Phys. B, Atomic, Molecular and Optical Physics. 37(7):
1541-51,2004.
Transient strain driven by a dense electron-hole plasma
M.F. DeCamp, D.A. Reis, A. Cavalieri, P.H. Bucksbaum, R. Clarke, R. Merlin, E.M.
Dufresne, D.A. Arms, A.M. Lindenberg, A.G. MacPhee, Z. Chang, B. Lings, J.S.
Wark, S. Fahy,
Phys. Rev. Lett.,91(16): 165502/1-4, 2003
Investigation of the onset and development of forward scattering in an
underdense plasma
J.D. Moody, E.A. Williams, S.H. Glenzer, P.E. Young, J. Hawreliak, A.
Gouveia, J.S. Wark,
Phys. Rev. Lett., 90(24): 245001/1-4, 2003.
Extension of the time-dependent dynamical diffraction theory to 'optical
phonon'-type distortions: application to diffraction from coherent acoustic and
optical phonons
P. Sondhauss and J.S. Wark, Acta Crystallogr. Section A Foundations of
Crystallography. A59 pt. 1: 7-13, 2003.
K-shell spectroscopy of an independently diagnosed uniaxially expanding
laser-produced aluminum plasma
D.M. Chambers, P.A. Pinto, J. Hawreliak, I.R. Al'Miev, A. Gouveia, P.
Sondhauss, E. Wolfrum, J.S. Wark, S.H. Glenzer, R.W. Lee, P.E. Young, O. Renner,
R.S. Marjoribanks, S. Topping,
Phys. Rev. E, 66(2): 026410/1-16, 2002.
Picosecond X-ray diffraction studies of laser-excited acoustic phonons in
InSb
J. Larsson, A. Allen, P.H. Bucksbaum, R.W. Falcone, A. Lindenberg, G.
Naylor, T. Missalla, D.A. Reis, K. Scheidt, A. Sjogren, P. Sondhauss, M. Wulff,
J.S. Wark,
Applied Physics A, Materials Science Processing, A75(4): 467-78, 2002.
A fluid-kinetic model for the two plasmon decay instability
A.C. Machacek and J.S. Wark,
Physics of Plasmas, 8(10): 4357-66, 2001.
Measurements of the XUV mass absorption coefficient of an overdense liquid
metal
E. Wolfrum, A.M. Allen, I. Al'Miev, T.W. Barbee Jr, P.D.S. Burnett, A.
Djaoui, C. Iglesias, D.H. Kalantar, R.W. Lee, R. Keenan, M.H. Key, C.L.S. Lewis,
A. Machacek, B.A. Remington,S.J. Rose, R. O'Rourke, J.S. Wark,
J. Phys. B, Atomic, Molecular and Optical Physics., 34(17): l565-70, 2001.
Detailed simulations of sonoluminescence spectra
P.D.S. Burnett, D.M. Chambers, D. Heading, A. Machacek, M. Schnittker, W.C.
Moss, P. Young, S. Rose, R.W. Lee, J.S. Wark,
J. Phys. B, Atomic, Molecular and Optical Physics., 34(16): L511-18, 2001.
Probing impulsive strain propagation with X-ray pulses
D.A. Reis, M.F. DeCamp, P.H. Bucksbaum, R. Clarke, E. Dufresne, M.
Hertlein, R. Merlin, R. Falcone, H. Kapteyn, M.M. Murnane, J. Larsson, T.
Missalla, J.S. Wark,
Phys. Rev. Lett., 86(14): 3072-5, 2001.
Anomalous elastic response of silicon to uniaxial shock compression on
nanosecond time scales
A. Loveridge-Smith, A. Allen, J. Belak, T. Boehly, A. Hauer, B. Holian, D.
Kalantar, G. Kyrala, R.W. Lee, P. Lomdahl, M.A. Meyers, D. Paisley, S. Pollaine,
B. Remington, D.C. Swift, S. Weber, J.S. Wark,
Phys. Rev. Lett., 86(11): 2349-52, 2001
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