Sub-100 Hz Intrinsic Linewidth 852 nm Silicon Nitride External Cavity Laser

TL;DR

This paper presents a compact external cavity laser at 852 nm with an intrinsic linewidth below 100 Hz, suitable for atomic physics applications, achieved through silicon nitride photonic integration and commercial gain chips.

Contribution

It introduces a low-loss silicon nitride external cavity laser with sub-100 Hz linewidth, tunability, and high side-mode suppression, advancing integrated laser technology for quantum sensing.

Findings

Linewidth below 100 Hz achieved

Wavelength tunability over 15 nm demonstrated

High side-mode suppression ratio over 50 dB attained

Abstract

We demonstrate an external cavity laser with intrinsic linewidth below 100 Hz around an operating wavelength of 852 nm, selected for its relevance to laser cooling and manipulation of cesium atoms. This system achieves a maximum CW output power of 24 mW, wavelength tunability over 15 nm, and a side-mode suppression ratio exceeding 50 dB. This performance level is facilitated by careful design of a low-loss integrated silicon nitride photonic circuit serving as the external cavity combined with commercially available semiconductor gain chips. This approach demonstrates the feasibility of compact integrated lasers with sub-kHz linewidth centering on the needs of emerging sensor concepts based on ultracold atoms and can be further extended to shorter wavelengths via selection of suitable semiconductor gain media.