Angus Harvey Jones

Artificial structures that exhibit narrow resonance features are key to a myriad of scientific advances and technologies. In particular, exploration of the terahertz (THz) spectrum—the final frontier of the electromagnetic spectrum—would greatly benefit from high-quality resonant structures. Here we present a new paradigm of terahertz silicon disc microresonators with subwavelength thickness. Experimental results utilizing continuous-wave THz spectroscopy establish quality factors in excess of 120,000 at 0.6 THz. Reduction of the disc thickness to a fraction of the wavelength reduces the losses from the silicon substrate and paves the way to unparalleled possibilities for light–matter interaction in the THz frequency range.

The terahertz spectrum provides tremendous opportunities for broadband gas-phase spectroscopy, as numerous molecules exhibit strong fundamental resonances in the THz frequency range. However, cutting-edge THz gas-phase spectrometer require cumbersome multi-pass gas cells to reach sufficient sensitivity for trace level gas detection. Here, we report on the first demonstration of a THz gas-phase spectrometer using a sub-wavelength thick ultrahigh-Q THz disc microresonator. Leveraging the microresonator’s ultrahigh quality factor in excess of 120,000 as well as the intrinsically large evanescent field, allows for the implementation of a very compact spectrometer without the need for complex multi-pass gas cells. Water vapour concentrations as low as 4 parts per million at atmospheric conditions have been readily detected in proof-of-concept experiments.

We report on the first demonstration of an anomalous blue-shift of whispering-gallery modes (WGMs) using metallic substrates. The results allow for frequency tuning of WGMs essential for numerous applications, and establish novel insights into the anomalous blue-shift of WGM cavity systems.

We investigate thermal tuning of an ultra-high quality (Q) terahertz (THz) whispering-gallery mode resonator (WGMR) made of low loss silicon. The Si THz WGMR can be continuously tuned with a rate of about 29 MHz/K in the frequency range from 650 GHz to 666 GHz. Furthermore, we utilize the Si WGMR to extract the thermo-optic coefficient of Si at 459 GHz and 659 GHz in the temperature range from 295 K to 363 K.