Opportunities for graduate research

Here we describe potential D.Phil. research projects which could start in October 2018.

Ultrafast X-ray imaging

High harmonic generation (HHG) is an extreme nonlinear process which can occur when an intense laser pulse ionizes a gas, resulting in the emission of radiation with frequencies equal to the odd harmonics of the driving laser.  These harmonics can extend to very high orders, as high as several hundred, corresponding to generated wavelengths in the soft x-ray region.   This short-wavelength radiation has been shown to have high spatial and temporal coherence, allowing highly collimated beams to be generated with pulse durations as short as approximately 100 attoseconds.  As such, HHG finds applications in probing ultrafast processes such as chemical reactions and material dynamics.

In collaboration with Profs Ian Walmsley and Alexander Korsunsky (Engineering Science), we have been awarded funding from EPSRC to support a four-year programme on table-top femtosecond x-ray dynamical imaging. Our role is to use femtosecond optical parametric amplifiers (OPAs) to determine the optimum driving laser wavelength for generating x-rays of a given photon energy. We will also use the new OPAs to investigate methods for increasing the intensity of the harmonic beam by quasi-phase-matching.

The bright x-ray beams generated by these methods will be used for coherent diffraction imaging. This method images objects without additional optics (which are not available at these wavelengths); it does so by recording the intensity diffraction pattern of the object and using sophisticated algorithms to overcome the "phase-retrieval problem" in recreating the object.

We will use the wavelength-tunable X-ray sources developed in our research programme  to image specific elements in a sample. As a test of these ideas, in collaboration with colleagues in the Department of Engineering, we will the size and shape of particles formed in precipitation-strengthened Al alloy.

We wish to take on one or more graduate students to work on this project.

 
  1. J. Miao, T. Ishikawa, I.K. Robinson, and M.M. Murnane, "Beyond crystallography: Diffractive imaging using coherent x-ray light sources," Science 348 530 (2015).
  2. R. L. Sandberg,A. Paul, D. A. Raymondson, S. Hadrich, D. M. Gaudiosi, J. Holtsnider, R. I. Tobey, O. Cohen, M. M. Murnane, and H. C. Kapteyn, "Lensless Diffractive Imaging Using Tabletop Coherent High-Harmonic Soft-X-Ray Beams," Phys. Rev. Lett. 99 098103 (2007).
  3. K. O’Keeffe, T. Robinson, and S. M. Hooker, "Quasi-phase-matching high harmonic generation using trains of pulses produced using an array of birefringent plates," Optics Express 20 6236-6247 (2012).
  4. L. Z. Liu, K. O'Keeffe, and S. M. Hooker, "Optical rotation quasi-phase-matching for circularly polarized high harmonic generation," Opt. Lett. 37 167066 (2012).
  5. L. Z. Liu, K. O'Keeffe, and S. M. Hooker, "Quasi-phase-matching of high-order-harmonic generation using polarization beating in optical waveguides," Phys. Rev. A 85  053823 (2012).
  6. D.T. Lloyd, K. O'Keeffe, and S.M. Hooker," Complete spatial characterization of an optical wavefront using a variable-separation pinhole pair," Opt. Lett. 38 1173-1175 (2013).

Applications for projects in this research area should be made to the sub-department of Atomic & Laser Physics, as described hereYou should state clearly in your application that you would like to work in the area of high-harmonic generation and ultrafast X-ray imaging (this will ensure that your application is seen by the correct potential supervisors).

Further information about research projects available in Atomic & Laser Physics can be found here.

Questions about the procedure for applying for graduate work in this area should be addressed to Monika Porada.

Laser-driven plasma accelerators

Plasma accelerators utilize the enormous electric fields formed within plasma waves to accelerate charged particles to high energies in a fraction of the distance needed in a conventional particle accelerator. You can find further details of our research programme in this area on our Research page.

Our lead academics are all members of the John Adams Institute (JAI), working in Oxford's sub-departments of Particle Physics and in Atomic & Laser Physics. We collaborate closely with JAI at Imperial College and with groups at DESY, Jena, MPQ and LBNL. Some experiments are undertaken in our laboratories in Oxford, at facilities based at the Rutherford Appleton Laboratory (just outside Oxford), or with our collaborators in the USA and Europe.

Our work on laser-driven plasma accelerators is in four areas: (i) investigation of techniques for controlling the injection of electrons into the plasma wakefield; (ii) development of new techniques for driving plasma accelerators, such as multi-pulse laser wakefield acceleration; (iii) development of techniques for driving the intense driving laser pulse over 100s of mm; and (iv) development of applications of laser-driven plasma accelerators, particularly their application to the generation of x-rays. We pursue these goals by both experiment and numerical modelling.

Projects available to start in 2018

We are looking for graduate students to work on many aspects of laser-driven plasma accelerators, starting October 2018.

There is scope for up to three new graduate students to work on numerical simulations and experiments exploring one or more of the following topics:

  •   Controlled injection in plasma accelerators driven by single and multiple laser pulses
  •   Generation of betatron radiation and its application to medical and biological imaging
  •   Simulations of MP-LWFAs driven by novel kilohertz, ultrafast laser systems
  •   Investigation of beam loading effects in MP-LWFAs
  •   Demonstration of electron acceleration in MP-LWFAs
  •   Start-to-end simulations of MP-LWFAs and outline design and assessment of their potential performance
  •   Extending the acceleration length in plasma accelerators by tailoring the longitudinal plasma profile

As far as possible we will seek to tailor the blend of these topics to match the strengths and preferences of graduate students joining us.

  1. J. Cowley, C. Thornton, C. Arran, R. J. Shalloo, L. Corner, G. Cheung, C. D. Gregory, S. P. D. Mangles, N. H. Matlis, D. R. Symes, R. Walczak, and S. M. Hooker, "Excitation and Control of Plasma Wakefields by Multiple Laser Pulses," Phys. Rev. Lett. 119 044802 (2017).
  2. S. M. Hooker, R. Bartolini, S. P. D. Mangles, A. Tünnermann, L. Corner, J. Limpert, A. Seryi, & R. Walczak, "Multi-Pulse Laser Wakefield Acceleration: A New Route to Efficient, High-Repetition-Rate Plasma Accelerators and High Flux Radiation Sources," J. Phys. B 47 234003 (2014).
  3. S. M. Hooker, "Developments in laser-driven plasma accelerators," Nature Photonics 775–782 (2013).
  4. N. Bourgeois, J. Cowley and S. M. Hooker, "Two-Pulse Ionization Injection into Quasilinear Laser Wakefields," Phys. Rev. Lett. 111 155004 (2013).
  5. W. P. Leemans, S. M. Hooker et al., "GeV electron beams from a centimetre-scale accelerator," Nature Physics 696 (2006),
  6. T.P. Rowlands-Rees, S. M. Hooker et al., "Laser-Driven Acceleration of Electrons in a Partially Ionized Plasma Channel," Phys. Rev. Lett. 100 105005 (2008)
  7. M. Fuchs, F. Gruner, S. Karsch, S. M. Hooker et al., "Laser-driven soft-X-ray undulator source," Nature Physics 826 (2009)
  8. T. Ibbotson, S. M. Hooker et al., "Laser-wakefield acceleration of electron beams in a low density plasma channel," Phys. Rev. ST Acc. Beams 13 031301 (2010).
  9. S. I. Bajlekov, W. M. Fawley, C. B. Schroeder, R. Bartolini, and S. M. Hooker, "Simulation of free-electron lasers seeded with broadband radiation," Phys. Rev ST Acc. Beams 14 060711 (2011).
  10. S. Kneip, K. Krushelnick, Z. Najmudin et al.,"Bright spatially coherent synchrotron X-rays from a table-top source," Nature Physics 980 (2010).

Applications for projects in this research area should be made to the sub-department of Particle Physics, as described hereYou should state clearly in your application that you would like to work in the area of laser-driven plasma accelerators (this will ensure that your application is seen by the correct potential supervisors).

Further information about research projects available in the John Adams Institute on the JAI's web pages.

Questions about the procedure for applying for graduate work in laser-plasma accelerators at Oxford should be addressed to  Sue Geddes.

 

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