Ultrafast optical techniques provide powerful probes of different states of matter, using light pulses that have femtosecond duration. Our activities span a number of areas:
studying the dynamics of the light-matter interaction in novel compounds and nanomaterials via terahertz spectroscopy and pump-probe methods,
terahertz medical imaging and spectroscopy,
developing methods and components for terahertz imaging and terahertz spectroscopy.
Ultrafast and terahertz spectroscopy facilities
The Group has four labs in the Physics and Materials and Analytical Sciences buildings. Read more about our experimental capabilities in terahertz science and technology. We also contribute to WCUS, a joint activity between Physics and Chemistry Departments at Warwick.
M.G. Burdanova, A.P. Tsapenko, M.V. Kharlamova, E.I. Kauppinen, B.P. Gorshunov, J. Kono and J. Lloyd-Hughes
Advanced Optical Materials 2101042 (Sept 2021)
Terahertz (THz) spectroscopy is an ideal non-contact and non-destructive technique that probes the electrical conductivity of nanomaterials. This review presents the current status of research in the THz properties of quasi-1D materials, such as nanotubes (NTs) and NT heterostructures. The detailed description of THz experimental methods (THz time-domain spectroscopy, optical pump-THz probe spectroscopy) and conductivity extraction methods are presented along with the physical models (Drude, plasmon, effective medium theories, etc.) supporting them. Optoelectronic applications, such as optical modulators, switches, and shielding devices, are discussed and illustrate a bright future for these materials.
C.D.W. Mosley, J. Deveikis and J. Lloyd-Hughes
Applied Physics Letters 119121105 (Sept 2021)
Full control of the ellipticity of broadband pulses of THz radiation, from linear to left- or right-handed circular polarization, was demonstrated via a four-pixel photoconductive emitter with an integrated achromatic waveplate. Excellent polarization purity and accuracy were achieved, with Stokes parameters exceeding 97% for linear and circular polarization, via a robust scheme that corrected electrically for polarization changes caused by imperfect optical elements. Furthermore, to assess the speed and precision of measurements of the THz polarization, we introduced a figure of merit, the standard error after one second of measurement, found to be 0.047° for the polarization angle.
M.G. Burdanova, M. Liu, M. Staniforth, Y. Zheng, R. Xiang, S. Chiashi, A. Anisimov, E. I. Kauppinen, S. Maruyama and J. Lloyd-Hughes
Advanced Functional Materials 2104969 (Sept 2021)
Strong intertube excitonic coupling is demonstrated in 1D van der Waals heterostructures by examining the ultrafast response of radial C/BN/MoS2 core/shell/skin nanotubes to femtosecond infrared light pulses. Remarkably, infrared excitation of excitons in the semiconducting carbon nanotubes (CNTs) creates a prominent excitonic response in the visible range from the MoS2 skin, even with infrared photons at energies well below the bandgap of MoS2. Via classical analogies and a quantum model of the light–matter interaction these findings are assigned to intertube excitonic correlations. Dipole–dipole Coulomb interactions in the coherent regime produce intertube biexcitons, which persist for tens of femtoseconds, while on longer timescales (>100 ps) hole tunneling—from the CNT core, through the BN tunnel barrier, to the MoS2 skin—creates intertube excitons. Charge transfer and dipole–dipole interactions thus play prominent roles on different timescales, and establish new possibilities for the multi-functional use of these new nanoscale coaxial cables.
R.J. Kashtiban, M.G. Burdanova, A. Vasylenko, J. Wynn, P.V.C. Medeiros, Q. Ramasse, A.J. Morris, D. Quigley, J. Lloyd-Hughes and J. Sloan
ACS Nano 1513389 (Aug 2021)
One-dimensional (1D) atomic chains of CsI were previously reported in double-walled carbon nanotubes with ∼0.8 nm inner diameter. Here, we demonstrate that, while 1D CsI chains form within narrow ∼0.73 nm diameter single-walled carbon nanotubes (SWCNTs), wider SWCNT tubules (∼0.8–1.1 nm) promote the formation of helical chains of CsI 2 × 1 atoms in cross-section. These CsI helices create complementary oval distortions in encapsulating SWCNTs with highly strained helices formed from strained Cs2I2 parallelogram units in narrow tubes to lower strain Cs2I2 units in wider tubes. The observed structural changes and charge distribution were analyzed by density-functional theory and Bader analysis. CsI chains also produce conformation-selective changes to the electronic structure and optical properties of the encapsulating tubules. The observed defects are an interesting variation from defects commonly observed in alkali halides as these are normally associated with the Schottky and Frenkel type. The energetics of CsI 2 × 1 helix formation in SWCNTs suggests how these could be controllably formed.