Ultra-high precision comb-locked terahertz frequency-domain spectroscopy of whispering-gallery modes

TL;DR

This paper introduces a novel terahertz spectrometer with comb-locked frequency synthesis, achieving ultra-high resolution and stability for analyzing whispering-gallery modes with rapid data acquisition and precise frequency calibration.

Contribution

The work presents a new terahertz spectrometer capable of kilohertz resolution and rapid spectral acquisition, enabling detailed analysis of whispering-gallery modes with unprecedented precision.

Findings

Achieved sub-20kHz resolution over 36GHz spectral range

Observed minute red and blue shifts in mode families

Demonstrated stable, rapid spectral measurements with high repeatability

Abstract

We demonstrate the capabilities of a novel frequency-domain terahertz spectrometer based on a comb-locked frequency synthesizer, which provides absolute frequency calibration. The inherent stability and repeatability of the scans allow for the combination of fast data acquisition with an average time-limited signal-to-noise ratio. We demonstrate kilohertz level frequency resolution in terahertz precision spectroscopy of ultrahigh quality whispering-gallery-mode resonators. Spectra covering multiple free spectral ranges (>36GHz) with sub-20kHz resolution are acquired in 5s. We analyse the coupling behaviour and temperature tuning of single resonances and, for the first time, observe minute red and blue shifts of different mode families. The experimental results are supported with finite element simulations.