PhD Projects
The PhD project descriptions listed below are provided to
give applicants a flavour of what research study is available. For further
information contact Darren Graham.
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Terahertz driven linac: Shrinking the size and cost of particle
accelerators
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Terahertz
spintronics: Enabling the exploitation of electron
spin
Group
Members
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Group Leader
Darren Graham, MPhys (Hons), Ph.D., FHEA, MInstP
Senior Lecturer in Physics
Department of Physics and Astronomy, The University of Manchester
E-mail: Darren.Graham@manchester.ac.uk
Twitter: @DMGrahamTHz
Google Scholar - https://scholar.google.co.uk/citations?user=SO6OV-cAAAAJ&hl=en
The University of Manchester staff
profile
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Morgan
Hibberd, MPhys (Hons), Ph.D.
Post-doctoral Research Associate
Department of Physics and Astronomy, The University of Manchester
E-mail: Morgan.Hibberd@manchester.ac.uk
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Charlotte
Bull, MPhys (Hons), Ph.D.
Post-doctoral Research Associate
Department of Physics and Astronomy & Department of Computer Science,
The University of Manchester
E-mail: charlotte.bull@manchester.ac.uk
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PhD
Students
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Vasileios Georgiadis
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Simmone Hewett
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Ruidong Ji
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Cheng-Han
Lin
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Christopher Shaw
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Selected Publications
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Spintronic terahertz emitters: Status
and prospects from a materials perspective,
Bull, C., Hewett, S. M., Ji,
R., Lin, C.-H., Thomson, T., Graham, D. M. & Nutter, P. W.,
Applied Physics Letters Materials 9, 090701 (2021), DOI: 10.1063/5.0057511 Selected as Editor’s Pick
Spintronic
terahertz (THz) emitters, consisting of ferromagnetic (FM)/non-magnetic
(NM) thin films, have demonstrated remarkable potential for use in THz
time-domain spectroscopy and its exploitation in scientific and industrial
applications. In this review, we present a comprehensive overview of the
experimental and theoretical findings that have led to the development of
spintronic THz emitters, which hold promise for use in a wide range of THz
applications. We summarize the current understanding of the mechanisms that
contribute to the emission of THz radiation from the spintronic heterostructures and explore how the material
properties contribute to the emission process.
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Dispersion in dielectric-lined
waveguides designed for terahertz-driven deflection of electron beams,
Georgiadis, V., Healy, A. L., Hibberd, M., Burt, G., Jamison, S.
P. & Graham, D. M., Applied Physics Letters 118, 144102 (2021), DOI: 10.1063/5.0041391 Selected as Editor’s Pick
We have developed
dielectric-lined rectangular waveguide structures for THz-driven ultrafast
deflection of 100 keV electron beams. The
structures were designed to achieve THz phase velocity matching with
co-propagating electron bunches. The phase-matching capability was
experimentally confirmed through time-frequency analysis of the broadband
coherent THz transmission measured by electro-optic sampling. We determined
the propagation constants for both the dielectric-lined waveguide structure
and the integrated input coupling horn.
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Acceleration of relativistic beams using
laser-generated terahertz pulses, Hibberd, M. T., Healy, A., Lake, D.,
Georgiadis, V., Smith, E., Finlay, O. J., Pacey, T., Jones, J. K.,
Saveliev, Y., Walsh, D. A., Snedden, E. W., Appleby, R., Burt, G., Graham,
D. M. & Jamison, S. P., Nature Photonics (2020), DOI: 10.1038/s41566-020-0674-1,
Free access to a view-only version
We demonstrate acceleration of a relativistic
electron beam in a THz-driven linear accelerator. Narrowband THz pulses
were phase-velocity-matched with 35 MeV, 60 pC
electron bunches, imparting multi-cycle energy modulation to chirped (6 ps) bunches and injection-phase-dependent energy gain
(up to 10 keV) to sub-cycle (2 ps) bunches. These results establish a route to
whole-bunch linear acceleration of sub-picosecond particle beams, directly
applicable to scaled-up and multi-staged concepts capable of preserving
beam quality.
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Magnetic-field tailoring of the terahertz polarization emitted from a
spintronic source
Hibberd, M. T., Lake, D. S., Johansson, N. A. B.,
Thomson, T., Jamison, S. P., and
Graham, D. M.,
Applied Physics Letters 114, 031101 (2019), DOI: 10.1063/1.5055736
We demonstrate a method to
create arbitrary terahertz (THz) polarization profiles by exploiting the
magnetic field-dependent emission process of a spintronic source. As a
proof-of-concept, we show that by applying a specific magnetic field
pattern to the source, it is possible to generate a quadrupole-like THz
polarization profile. This unique ability to generate any desired THz
polarization profile opens up possibilities for schemes such as rotatable
polarization spectroscopy and for efficient mode coupling in various
waveguide designs.
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Demonstration of sub-luminal propagation of single-cycle terahertz
pulses for particle acceleration,
Walsh, D. A., Lake, D. S., Snedden, E. W., Cliffe,
M. J., Graham, D. M. & Jamison, S. P.,
Nature Communications. 8, 421
(2017),
DOI: 10.1038/s41467-017-00490-y
We describe and demonstrate a method for
generating single-cycle terahertz pulses that propagate with an effective
sub-luminal phase velocity, and without distortion during propagation. This novel travelling source approach
fulfils the requirement for a sub-luminal phase velocity in laser-driven
particle acceleration schemes without the need for dispersive structures or
waveguides to extend the field-particle interaction.
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Dielectric response of wurtzite gallium
nitride in the terahertz frequency range, Hibberd, M., Frey, V.,
Spencer, B., Mitchell, P., Dawson, P., Kappers, M.
J., Oliver, R. A., Humphreys, C. J. & Graham, D. M., Solid State Communications. 247, 68-71 (2016), DOI: 10.1016/j.ssc.2016.08.017
In this work the intrinsic, anisotropic, dielectric properties of wurtzite gallium nitride in the spectral range of 0.5–11 THz
are determined from a semi-insulating m-plane
gallium nitride single crystal, providing measurements of the refractive
indices and absorption coefficients. These
results will provide the essential material parameters to assist in the
future design of terahertz devices based on wurtzite
GaN.
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Terahertz
cyclotron resonance spectroscopy of an AlGaN/GaN heterostructure using a
high-field pulsed magnet and an asynchronous optical sampling technique,
Spencer, B. F., Smith, W. F., Hibberd, M. T., Dawson, P., Beck, M.,
Bartels, A., Guiney, I., Humphreys, C. J. & Graham, D. M., Applied Physics Letters. 108,
212101 (2016), DOI: 10.1063/1.4948582
We have shown that by modifying an asynchronous optical sampling
detection scheme THz cyclotron resonance spectroscopy may be performed with
a high-field pulsed magnet in a laboratory environment. The development of
this instrument has allowed us to determine the fundamental properties of a
two-dimensional electron gas in an AlGaN/GaN heterostructure.
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Longitudinally
polarized single-cycle terahertz pulses generated with high electric field
strengths, Cliffe, M. J., Graham, D. M.
& Jamison, S. P., Applied Physics Letters. 108, 221102 (2016), DOI: 10.1063/1.4953024
By using a matched pair of polarity inverted MgO:SLN crystals as an optical
rectification source, we demonstrate the generation of strong on-axis
longitudinally polarized single-cycle terahertz radiation, with electric
field amplitudes in excess of 11 kV/cm. In contrast to segmented waveplate sources, the single-cycle terahertz temporal
profile is maintained hence maximizing the attainable electric field
strength.
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Generation
of longitudinally polarized terahertz pulses with field amplitudes
exceeding 2 kV/cm, Cliffe, M. J., Rodak, A., Graham, D. M. & Jamison, S. P., Applied Physics Letters. 105,
191112 (2014), DOI: 10.1063/1.4901904
We demonstrate the generation of near-single cycle longitudinally
polarized terahertz radiation using a large-area radially biased
photoconductive antenna with a longitudinal field amplitude in excess of 2
kV/cm. The 76 mm diameter antenna was biased with a voltage of up to 100 kV
applied over concentric electrodes. By tightly focusing the radiation
emitted from the antenna, we obtained a longitudinal field amplitude of
2.22 kV/cm.
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