THz Research

Key personnel: Dr Euan Hendry.

THz Plasmonics

In the past decade there has been a surge of interest in surface plasmon-polaritons (SPPs), light waves bound to interface of a conductor by free charges (see fig. 1). To date, most of the research into SPPs has been limited to frequencies near metallic plasma frequencies (i.e. in the visible and IR spectral regions), where the electric field of SPPs is strongly confined to a thin region at the metal surface. The capability of SPPs to confine electromagnetic energy at the interface of a conductor makes them useful for many applications where efficient guiding of light on very small length scales is important. Such applications successfully demonstrated in the lab environment include sub-wavelength microscopy and optics, non-linear optics and photolithography. Furthermore, since SPPs can support higher frequencies than electrical cables, SPPs have also been proposed as a means of efficiently transmitting information.

Here, we explore the potential for developing new THz components and sensors based on semiconductor SPPs. Semiconductors, with plasma frequencies in the THz range, offer the potential for sustaining SPPs at THz frequencies. Furthermore, semiconductors offer a unique and hugely beneficial advantage over metals: since the surface charge density can be modified by, for example chemical doping, plasma frequencies and SPP properties can be tailored within the THz frequency range. An extension of this is the exciting possibility of all-optical plasmon control, i.e. ‘photo-doping’ a semiconductor with visible frequency light, so that plasma frequencies may be tuned by a visible frequency light source. Using ultrafast laser sources for this purpose, the properties of THz SPP modes can therefore be tailored and switched on very fast (picosecond) timescales, something that is essential for high-bandwidth and/or time resolved applications