Recruitment

PhD research studentships

We are looking for graduate students to work in the following areas, starting October 2017.

Ultrafast lensless imaging with OPA-driven high-harmonic generation

Figure 1.: The SCIMITAR technique for simultaneous measurement of the transverse variation of the intensity, wave-front and coherence of an X-ray beam.

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.

CDI_reconstruction.gif

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. The concept is illustrated in the figure to the right: here the reconstructed amplitude (left) and phase (right) are shown at several iteration steps, starting from the calculated diffraction patter. We think M. Fourier would like this!

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.

Further reading:

  1. J. Miao, T. Ishikawa, I.K. Robinson, and M.M. Murnane, "Beyond crystallography: Diffractiveimaging 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).

Plasma accelerators

For information on opportunities for graduate study in this area see our new laser-plasma accelerators page.

Further information

Further information about research projects available in the sub-department of atomic and laser physics and a description of the application procedure may be found on Department's web pages. Questions about applications in the area of Atomic and Laser Physics should be addressed to Monika Porada.