Research Bio

My research career has focused on understanding interactions between optical and electronic systems, with the vision of engineering new device functionality. More specifically, I am interested in creating a new classes of infrared optical components, capable of producing better thermal cameras, optical communication and spectroscopic sensors for gas and pollutant detection. To do so I leverage the phenomenon of a ‘surface polariton’, which occurs in a range of different materials including metals, semiconductors and the broad class of 2D materials. Surface polaritons are evanescent waves which propagate along a surface, and confine light to dimensions far below the free space wavelength, allowing a more efficient light-matter interaction when properly engineered. Determining the properties of these modes and the materials that support them is a critical part of my research.

JAP - Figure 1-01
The dispersion relation of Surface Polaritons (a) . Whilst the wavevector (2π/λ) of light is linear with frequency, for a surface polariton the wavector diverges and becomes extremely large (as shown in the black). In order to couple to this type of wave we can use a range of different experimental techniques, including prism coupling (b)-(c), grating coupling (d) and nanoparticle scattering (e). This figure is taken from Folland et. al., JAP, 125, 191102 (2019). 

Highlights of my work include the first demonstration of a graphene controlled THz laser (Science, 2016), coherent detection of THz laser signals by fibre techniques (Applied Physics Letters, 2017) and the first demonstration of hyperbolic polariton refraction (Nature Comms, 2018). These results demonstrate that new types of functionality can be realized by leveraging surface polariton modes.

Working in the lab
Infrared microscopy allows the measurement of samples down to 20 microns. 

Experimentally, my work leverages broad range infrared (λ=1-30μm) and terahertz (λ=30-100μm) optical spectroscopy techniques, which allows me to study low energy phenomena (including phonons and intra-band transitions) in a range of different materials. Whilst my research typically work with a range of solid-state materials and devices, these techniques are equally applicable see

Dr. Thomas G Folland.