Sub-kHz linewidth narrowing of a mid-infrared OPO idler frequency by direct cavity stabilization

TL;DR

This paper demonstrates a technique to significantly narrow the linewidth of a mid-infrared OPO idler frequency by directly stabilizing it to a reference cavity using Pound-Drever-Hall locking, achieving sub-kHz linewidths.

Contribution

It introduces a method for direct cavity stabilization of a mid-infrared OPO idler, achieving linewidth narrowing to sub-kHz levels, which was not previously demonstrated.

Findings

Linewidth narrowed to 920 Hz over 100 ms

Residual frequency noise below 10^3 Hz^2/Hz

Potential for Hz-level spectral purity

Abstract

We stabilize the idler frequency of a singly-resonant optical parametric oscillator directly to the resonance of a mid-infrared Fabry-P\'erot reference cavity. This is accomplished by the Pound-Drever-Hall locking scheme, controlling either the pump laser or the resonant signal frequency. A residual relative frequency noise power spectral density below 10$^3$ Hz$^2$/Hz is reached, with a Gaussian linewidth of 920 Hz over 100 ms, which demonstrates the potential for reaching spectral purity down to the Hz level by locking the optical parametric oscillator against a mid-infrared cavity with state-of-the-art superior performance.