Terahertz Synthetic FM Triplet for Distortion-Free Stabilization and Lamb-Dip Spectroscopy

TL;DR

This paper introduces a novel terahertz frequency stabilization method using a synthetic FM triplet, enabling distortion-free spectroscopy and Lamb-dip observation in complex molecular spectra, advancing molecular clock technology.

Contribution

The paper presents a new synthetic FM triplet technique that eliminates modulation sideband interference in terahertz spectroscopy, improving spectral purity and stability.

Findings

Achieved fractional frequency instability of 1e-9 at 1 second

Successfully observed Lamb-dips in acetonitrile spectra

Demonstrated high-fidelity, distortion-free spectral waveforms

Abstract

We demonstrate a distortion-free terahertz frequency stabilization technique using a "synthetic FM triplet" to overcome modulation sideband interference associated with high-density spectral lines in molecular clocks. By applying this method to the rotational transitions of acetonitrile (CH$_3$CN), we successfully generated clean derivative waveforms free from inter-line interference, achieving a fractional frequency instability of $1 \times 10^{-9}$ at an averaging time of $1~\mathrm{s}$. Furthermore, we report the observation of Lamb-dips using this high-fidelity approach. Our results establish acetonitrile as a promising candidate for high-agility molecular clocks and provide a robust solution for precision spectroscopy of molecules with complex hyperfine structures.