Terahertz multi-heterodyne spectroscopy using laser frequency combs

TL;DR

This paper demonstrates the first multi-heterodyne spectroscopy using terahertz quantum cascade laser combs, achieving high signal-to-noise ratios and broad spectral coverage with potential for room-temperature operation and pulsed mode extension.

Contribution

It introduces a novel multi-heterodyne spectroscopy technique with terahertz quantum cascade laser combs, enabling broadband, high-resolution measurements with minimal integration time.

Findings

Peak SNR exceeding 60 dB with 100 μs integration

Spectral coverage greater than 250 GHz at 2.8 THz

Effective broadband transmission measurement of etalon samples

Abstract

Frequency combs based on terahertz quantum cascade lasers feature broadband coverage and high output powers in a compact package, making them an attractive option for broadband spectroscopy. Here, we demonstrate the first multi-heterodyne spectroscopy using two terahertz quantum cascade laser combs. With just 100 $\mu$s of integration time, we achieve peak signal-to-noise ratios exceeding 60 dB and a spectral coverage greater than 250 GHz centered at 2.8 THz. Even with room-temperature detectors we are able to achieve peak signal-to-noise ratios of 50 dB, and as a proof-of-principle we use these combs to measure the broadband transmission spectrum of etalon samples. Finally, we show that with proper signal processing, it is possible to extend the multi-heterodyne spectroscopy to quantum cascade laser combs operating in pulsed mode, greatly expanding the range of quantum cascade lasers that could be suitable for these techniques.