Ultrafast & Terahertz Photonics Group
Ultrafast optical techniques provide powerful probes of different states of matter, using light pulses that have femtosecond duration. In Warwick our activities span a number of areas:
|
Group facilitiesThe Group has labs across the campus, in the main Physics building, Materials and Analytical Sciences, and Millburn House. Read more about our experimental capabilities in terahertz science and technology. We also run the Warwick Centre for Ultrafast Spectroscopy Research Technology Platform. We make use of a wide range of Warwick's excellent materials analysis equipment, including X-ray diffraction, Raman spectroscopy, electron microscopy and magnetometry. |
Join the group!Please get in touch if you are interested in a PhD or MSc by Research in the group. We have two funded PhD projects available for 2024 start: with Dr Adam Wright on polaritons in perovskite solar cell materialsLink opens in a new window, and Prof. Emma MacPherson on THz robotic probes of skin cancerLink opens in a new window. Group, Theses & PhotosContact details for our current group members and our photo gallery. For recent theses from the group, please see here. |
Research areas
Nanomaterials
We use pump/probe spectroscopy to study how light and matter interact on femtosecond to nanosecond timescales. Using visible probes we can track electronic processes, while infrared radiation lets us study vibrational states of molecules and atomic-scale defects in semiconductors.
Recent papers:
The 3237 cm−1 diamond defect: Ultrafast vibrational dynamics, concentration calibration, and relationship to the N3VH0 defect
High-bandwidth perovskite photonic sources on silicon
Terahertz medical imaging
Performing in vivo studies of the THz properties of skin is a major initiative in the group, supported by the EPSRC Terabotics Programme GrantLink opens in a new window. We develop robust measurement protocols and test them on a statistically significant number of patients, cross-checking with other methods.
Recent papers:
Terahertz probe for real time in vivo skin hydration evaluation
Spectroscopic insight on impact of environment on natural photoprotectants
The 2023 terahertz science and technology roadmap
Semiconductors and Energy materials
A major strand of our research is to improve our knowledge of the fundamental science underpinning new semiconductor materials, such as metal-halide perovskites, which are often attractive for photovoltaic applications.
Recent papers:
Terahertz Emission via Optical Rectification in a Metal-Free Perovskite Crystal
High-bandwidth perovskite photonic sources on silicon
Resolving the Ultrafast Charge Carrier Dynamics of 2D and 3D Domains within a Mixed 2D/3D Lead-Tin Perovskite
Terahertz components, methods and techniques
We develop new THz devices and integrate them into novel systems designs that can perform THz imaging and THz spectroscopy faster, and with increased capabilities (e.g. polarisation control; robot-controlled probes).
Recent papers:
Simultaneous measurement of orthogonal terahertz fields via an emission multiplexing scheme
Optimum Optical Designs for Diffraction-Limited Terahertz Spectroscopy and Imaging Systems Using Off-Axis Parabolic Mirrors
The 2023 terahertz science and technology roadmap
Recent publication highlights [filter by topic: view all | highlights | THz | perovskites | nano | biomedical]
Cs1−xRbxSnI3 light harvesting semiconductors for perovskite photovoltaics
K.P. Marshall, S. Tao, M. Walker, D.S. Cook, J. Lloyd-Hughes, S. Varagnolo, A. Wijesekara, D. Walker, R.I. Walton and R.A. Hatton
Materials Chemistry Frontiers 2:1515 (June 2018) [ pdf ] [ ref ]
We show that films of the 3-dimensional perovskite Cs1−xRbxSnI3 can be prepared from room temperature N,N-dimethylformamide solutions of RbI, CsI and SnCl2 for x ≤ 0.5, and that for x ≤ 0.2 film stability is sufficient for utility as the light harvesting layer in inverted photovoltaic (PV) devices. Electronic absorption and photoluminescence spectroscopy measurements supported by computational simulation, show that increasing x increases the band gap, due to distortion of the lattice of SnI6 octahedra that occurs when Cs is substituted with Rb, although it also reduces the stability towards decomposition. When Cs0.8Rb0.2SnI3 perovskite is incorporated into the model inverted PV device structure; ITO|perovskite|C60|bathocuproine|Al, an ∼120 mV increase in open-circuit is achieved which is shown to correlate with an increase in perovskite ionisation potential. However, for this low Rb loading the increase in band gap is very small (∼30 meV) and so a significant increase in open circuit-voltage is achieved without reducing the range of wavelengths over which the perovskite can harvest light. The experimental findings presented are shown to agree well with the predictions of density functional theory (DFT) simulations of the stability and electronic structure, also performed as part of this study.
Conduction properties of thin films from a water soluble carbon nanotube/hemicellulose complex
D. Shao, P. Yotprayoonsak, V. Saunajoki, M. Ahlskog, J. Virtanen, V. Kangas, A. Volodin, C. Van Haesendonck, M. Burdanova, C. D. W. Mosley and J. Lloyd-Hughes
Nanotechnology 29 145203 (Feb 2018) [ pdf ] [ ref ]
We have examined the conductive properties of a carbon nanotube (CNT) based thin film, which were prepared via dispersion in water by non-covalent functionalization of the nanotubes with xylan, a type of hemicellulose. Measurements of low temperature conductivity, Kelvin Probe Force Microscopy, and high frequency (THz) conductivity elucidated the intra-tube and inter-tube charge transport processes in this material. The measurements show excellent conductive properties of the as prepared thin films, with bulk conductivity up to 2000 S/cm. The transport results demonstrate that the hemicellulose does not seriously interfere with the inter-tube conductance.
Tracking a hysteretic and disorder-broadened phase transition via the electromagnon response in improper ferroelectrics
C. D. W. Mosley, D. Prabhakaran and J. Lloyd-Hughes
J. Phys. D: Applied Physics 51 084002 (Jan 2018) [ pdf ][ ref ]
We demonstrate that electromagnons can be used to directly probe the nature of a phase transition between magnetically ordered phases in an improper ferroelectric. The antiferromagnetic/paraelectric to antiferromagnet/ferroelectric phase transition in Cu1-xZnxO (x = 0, 0.05) alloys was tracked via the electromagnon response using terahertz time-domain spectroscopy, on heating and cooling through the phase transition. The transition was found to exhibit thermal hysteresis, confirming its first-order nature, and to broaden under the influence of spin-disorder upon Zn substitution. The energy of the electromagnon increases upon alloying, as a result of the non-magnetic ions modifying the magnetic interactions that give rise to the multiferroic phase and electromagnons. We describe our findings in the context of recent theoretical work that examined improper ferroelectricity and electromagnons in CuO from phenomenological and first-principles approaches.