Seeing the light: untapping terahertz

6 May 2020

Scientists from the University of Oxford’s Department of Physics have managed to record the full polarisation state of terahertz pulses by developing a nanowire-based sensor.

Terahertz radiation is a powerful tool for both fundamental scientific research and applications such as security screening, communications and medical imaging. To date, most terahertz detectors are sensitive to just one polarisation component however in research published in the journal Science this week the group demonstrated a nanotechnology-based semiconductor that records the full state of broadband pulses of terahertz light.

Measuring complex information

The device measures a huge amount of information from each light pulse including the amplitude, phase, polarisation angle and ellipticity at each of a comb of frequencies over a broad spectral range. This detector enables the study of complex materials, and in this research, the group exploited it to study metamaterials, which are thin artificial materials that can be used to control and manipulate light. Beyond aiding the development of artificial metamaterials, the device can be used for enhanced terahertz imaging and observe the motion of electrons in solids with femtosecond temporal resolution.

The research was a collaboration between Professor Michael Johnston’s group within Condensed Matter Physics at Oxford and researchers from the Australian National University (ANU) and University of Strathclyde. Design, fabrication and measurements were performed in Oxford, while ANU created the nanowire elements and the Strathclyde group developed and used a transfer printing technique to fabricate the crossed-nanowire networks at the core of the THz detector.

'Three dimensional cross-nanowire networks recover full terahertz state', Peng et al, Science 1 May 2020, Vol. 368, Issue 6490, pp. 510-513
DOI: 10.1126/science.abb0924

Science Research highlight of paper

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Physics in focus

New to physics? Look for the 'physics in focus' explanations to help you along the way...

What is terahertz radiation? You will be very familiar with visible light which your eyes detect and allow you to see what is around you. You may also have heard of X-rays which are used in medical imaging, as well as microwaves which can heat your food or transmit data to and from your mobile phone. In fact, radio waves, microwaves, light, X-rays and gamma rays are all the same phenomenon: they are all are oscillating electric and magnetic fields, which are called 'electromagnetic radiation' and travel at the speed of light in free space. The difference between them is how rapidly the electric and magnetic fields change.

Terahertz radiation is a type of electromagnetic wave that oscillates more quickly than microwaves but slower than visible light so the electric and magnetic field oscillate back and forth between 100 billion times a second (100GHz) and 20 thousand-billion times a second (20THz). This helps explain the term 'terahertz radiation': tera means a thousand-billion and hertz is defined as a cycle-per-second and named after the famous physicist Heinrich Hertz who first proved the existence of electromagnetic radiation.