A sub-40 mHz linewidth laser based on a silicon single-crystal optical cavity

TL;DR

This paper introduces a silicon-based optical cavity operating at 124 K that significantly reduces thermal noise, achieving unprecedented laser stability and a linewidth below 40 mHz, advancing optical metrology capabilities.

Contribution

It presents a novel silicon single-crystal cavity design that minimizes thermal noise and vibration effects, resulting in the most stable laser oscillator demonstrated to date.

Findings

Fractional frequency stability of 1E-16 at short time scales

Laser linewidth below 40 mHz at 1.5 μm

Optical quality factor of 4E15

Abstract

State-of-the-art optical oscillators based on lasers frequency stabilized to high finesse optical cavities are limited by thermal noise that causes fluctuations of the cavity length. Thermal noise represents a fundamental limit to the stability of an optical interferometer and plays a key role in modern optical metrology. We demonstrate a novel design to reduce the thermal noise limit for optical cavities by an order of magnitude and present an experimental realization of this new cavity system, demonstrating the most stable oscillator of any kind to date. The cavity spacer and the mirror substrates are both constructed from single crystal silicon and operated at 124 K where the silicon thermal expansion coefficient is zero and the silicon mechanical loss is small. The cavity is supported in a vibration-insensitive configuration, which, together with the superior stiffness of silicon crystal, reduces the vibration related noise. With rigorous analysis of heterodyne beat signals among three independent stable lasers, the silicon system demonstrates a fractional frequency stability of 1E-16 at short time scales and supports a laser linewidth of <40 mHz at 1.5 \mu m, representing an optical quality factor of 4E15.