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 are also happy to support postdoctoral researchers to apply for fellowship schemes. ![]() 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.
![CNT](https://warwick.ac.uk/fac/sci/physics/research/condensedmatt/ultrafastphotonics/publications/burdanova2021toc.png?maxWidth=400)
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.
![Medical](https://warwick.ac.uk/fac/sci/physics/research/condensedmatt/ultrafastphotonics/publications/lindley-hatcher2021.jpg?maxWidth=400)
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.
![Electronically-delayed optical pump/THz probe spectroscopy on a variety of semiconductors](https://warwick.ac.uk/fac/sci/physics/research/condensedmatt/ultrafastphotonics/research/eoptp.png?maxWidth=400)
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).
![Single-pixel](https://warwick.ac.uk/fac/sci/physics/research/condensedmatt/ultrafastphotonics/publications/stantchev2020.png?maxWidth=400)
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]
Landau polaritons in highly nonparabolic two-dimensional gases in the ultrastrong coupling regime
J. Keller, G. Scalari, F. Appugliese, S. Rajabali, M. Beck, J. Haase, C.A. Lehner, W. Wegscheider, M. Failla, M. Myronov, D.R. Leadley, J. Lloyd-Hughes, P. Nataf, and J. Faist
Physical Review B 101:075301 (Feb 2020) [ pdf ][ ref ]
We probe ultrastrong light-matter coupling between metallic terahertz metasurfaces and Landau-level transitions in high-mobility two-dimensional electron and hole gases. We utilize heavy-hole cyclotron resonances in strained Ge and electron cyclotron resonances in InSb quantum wells, both within highly nonparabolic bands, and compare our results to well-known parabolic AlGaAs/GaAs quantum well systems. Tuning the coupling strength of the system by two methods, lithographically and by optical pumping, we observe a behavior clearly deviating from the standard Hopfield model previously verified in cavity quantum electrodynamics: an opening of a lower polaritonic gap.
Ionic liquid gated carbon nanotube saturable absorber for switchable pulse generation
Y. Gladush, A. Mkrtchyan, D. Kopylova, A. Ivanenko, B. Nyushkov, S. Kobtsev, A. Kokhanovskiy, A. Khegai, M. Melkumov, M.G. Burdanova, M. Staniforth, J. Lloyd-Hughes and A.G. Nasibulin
Nano Letters 19 5836 (Aug 2019) [ pdf ] [ ref ]
Materials with electrically tunable optical properties offer a wide range of opportunities for photonic applications. The optical properties of the single-walled carbon nanotubes (SWCNTs) can be significantly altered in the near infrared region by means of electrochemical doping. The states’ filling, which is responsible for the optical absorption suppression under doping, also alters the nonlinear optical response of the material. Here, for the first time, we report that the electrochemical doping can tailor the nonlinear optical absorption of SWCNT films and demonstrate its application to control pulsed fiber laser generation. With a pump-probe technique we show that under an applied voltage below 2 V the photo-bleaching of the material can be gradually reduced and even turned to photo-induced absorption. Furthermore, we integrated a carbon nanotube electrochemical cell on a side-polished fiber to tune the absorption saturation and implemented it into the fully polarization-maintaining fiber laser. We show that the pulse generation regime can be reversibly switched between femtosecond mode locking and microsecond Q-switching using different gate voltages. This approach paves the road towards carbon nanotube optical devices with tunable nonlinearity.
Giant negative terahertz photoconductivity in controllably doped carbon nanotube networks
M.G. Burdanova, A.P. Tsapenko, D.A. Satco, R.J. Kashtiban, C.D.W. Mosley, M. Monti, M. Staniforth, J. Sloan, Y. Gladush, A.G. Nasibulin and J. Lloyd-Hughes
ACS Photonics 6 1058 (Mar 2019) [ preprint pdf ] [ supplemental info ] [ ref ]
A strong negative photoconductivity was identified in thin film networks of single-walled carbon nanotubes using optical pump, THz probe spectroscopy. The films were controllably doped, using either adsorption doping with different p-type dopant concentrations, or ambipolar doping using an ionic gate. While doping enhanced the THz conductivity and increased the momentum scattering rate, interband photoexcitation lowered the spectral weight and reduced the momentum scattering rate. This negative THz photoconductivity was observed for all doping levels, regardless of the chemical potential, and decayed within a few picoseconds. The strong many-body interactions inherent to these 1D conductors led to trion formation under photoexcitation, lowering the overall conductivity of the carbon nanotube network. The large amplitude of negative THz photoconductivity and the tunability of its recovery time with doping offer promise for spectrally wide-band ultrafast devices including THz detectors, polarizers and modulators.
Graphene controlled Brewster angle device for ultra broadband terahertz modulation
Z. Chen, X. Chen, L. Tao, K. Chen, M. Long, K. Yan, R.I. Stantchev, E. Pickwell-MacPherson & J.-B. Xu
Nature Communications 9 4909 (November 2018) [ pdf ] [ ref ]
Terahertz modulators with high tunability of both intensity and phase are essential for effective control of electromagnetic properties. Due to the underlying physics behind existing approaches there is still a lack of broadband devices able to achieve deep modulation. Here, we demonstrate the effect of tunable Brewster angle controlled by graphene, and develop a highly-tunable solid-state graphene/quartz modulator based on this mechanism. The Brewster angle of the device can be tuned by varying the conductivity of the graphene through an electrical gate. In this way, we achieve near perfect intensity modulation with spectrally flat modulation depth of 99.3 to 99.9 percent and phase tunability of up to 140 degree in the frequency range from 0.5 to 1.6 THz. Different from using electromagnetic resonance effects (for example, metamaterials), this principle ensures that our device can operate in ultra-broadband. Thus it is an effective principle for terahertz modulation.