Applications of high-power laser-matter interactions |
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Professor Simon M Hooker
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Our group undertakes work in two areas of high-intensity laser-matter interactions: lasers operating at x-ray wavelengths, and plasma accelerators. The very high laser powers required for both of these applications are achieved by generating laser pulses of modest energy, but which are very short in time. As an example, the laser in our laboratory generates pulses of light with an energy of around 100 mJ and with a duration of less than 50 femtoseconds (i.e. 50 × 10-15 s). The peak power of each pulse exceeds 2 terawatts (2 × 1012 W) – approximately equal to the output from all the power stations on Earth! When focused to a beam with a diameter of around 30 μm, the peak laser intensity is of order 1021 W m‑2. At this intensity the electric field of the electromagnetic wave exceeds the intra-atomic field binding valence electrons to atoms and ions, and as a consequence rapid optical field ionization (OFI) occurs. The plasma that is formed is an interesting gain medium for short-wavelength lasers operating in the extreme ultraviolet (100 nm – 30 nm) and soft x-ray (30 nm – 1 nm) spectral regions. We have a comprehensive experimental programme to investigate a wide variety of novel OFI lasers operating in this important region of the spectrum. At somewhat higher laser intensities – 1022 W m‑2 – laser pulses propagating through a plasma generate a longitudinal plasma wave which trails the laser pulse in much the same way as a wake follows a boat travelling across water. The electric fields in the plasma wave can reach 100 kilovolts per micron, at least a thousand times bigger than the accelerating fields used in conventional accelerators such as those at CERN. The prospect of a new generation of extremely compact particle accelerators generating particle beams with unique properties, and which could also drive novel radiation sources, is an attractive one. Our group plays a key role in a UK collaboration which is investigating compact laser-driven plasma accelerators and their applications. The applications outlined above, and others, require intense laser pulses to propagate through plasmas for lengths of 10 – 100 mm. However, diffraction and refraction of the laser light limit the effective laser-plasma interaction length to a few millimetres. In order to increase the interaction length it is necessary to channel the laser pulses, in much the same way that an optical fibre guides low-intensity laser light. Of course, at intensities of 1022 W m‑2 this is not trivial! Recently our group developed a new type of waveguide that guides intense laser pulses in a shaped plasma channel produced by a discharge in a narrow capillary. To date we have been able to guide laser pulses with a peak intensity of 1021 W m‑2 over lengths of up to 50 mm and with an energy transmission of around 90%. We are now further developing the waveguide, with particular emphasis on tailoring the properties of the plasma channel for short-wavelength lasers and plasma accelerators. |
Key PublicationsT. Robinson, K. O’Keeffe, M. Zepf, B. Dromey & S. M. Hooker, “Generation and control of ultrafast pulse trains for quasi-phase-matching high-harmonic generation” J. Opt. Soc. Am. B 27 763 (2010). M. Fuchs, R. Weingartner, A. Popp et al. “Laser-driven soft-x-ray undulator source” Nature Physics 5 826–829 (2009). J. Osterhoff, A. Popp, Z. Major et al. “Generation of stable, low-divergence electron beams by laser-wakefield acceleration in a steady-state-flow gas cell” Physical Review Letters 101 085002 (2008). T. P. Rowlands-Rees, C. Kamperidis, S. Kneip et al. “Laser-driven acceleration of electrons in a partially ionized plasma channel” Physical Review Letters 100 105005 (2008). A. Gonsalves, T. P. Rowlands-Rees, B. H. P. Broks, J. van der Mullen, & S. M. Hooker. “Transverse interferometry of a hydrogen-filled capillary discharge waveguide” Physical Review Letters 98 025002 (2007). T. Robinson, K. O’Keeffe, M. Landreman, S. M. Hooker, M. Zepf, & B. Dromey. “Simple techniquefor generating trains of ultrashort pulses” Optics Letters 32 2203–2205 (2007). M. Zepf, B. Dromey, M. Landreman, P. Foster, & S. M. Hooker. “Bright quasi-phase-matched soft-x-ray harmonic radiation from argon ions” Physical Review Letters 99 143901 (2007). W. Leemans, B. Nagler, A. J. Gonsalves, C. Toth, K. Nakamura, C. G. R. Geddes, E. Esarey, C. B.Schroeder, & S. M. Hooker. “GeV electron beams from a centimetre-scale accelerator” NaturePhysics 2 696–699 (2006). A. Butler, A. J. Gonsalves, C. M. McKenna, D. J. Spence, S. M. Hooker, S. Sebban, T. Mocek,I. Bettaibi, & B. Cros. “Demonstration of a collisionally excited optical-field-ionization XUV laser driven in a plasma waveguide” Physical Review Letters 91 205001 (2003). A. Butler, D. J. Spence, & S. M. Hooker. “Guiding of high-intensity laser pulses with a hydrogen-filledcapillary discharge waveguide” Physical Review Letters 89 185003 (2002). D. Spence & S. M. Hooker. “Investigation of a hydrogen plasma waveguide” Physical Review E 63015401 (2001).
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