Highly coherent two-color laser with stability below 3E-17 at 1 second

TL;DR

This paper demonstrates a highly coherent two-color laser system with fractional frequency instability below 3E-17 at 1 second, enabling ultra-precise measurements and low-noise microwave generation by overcoming thermal noise and phase noise limitations.

Contribution

The authors develop a synchronization method using an ultra-stable cavity and electro-optical frequency division to achieve unprecedented coherence in two-color lasers with large frequency spacings.

Findings

Achieved fractional frequency instability of 2.7E-17 at 1 second.

Demonstrated phase noise of -74 dBc/Hz at 1 Hz for 25 GHz microwave signals.

Set a new record for two-point frequency division in photonic microwave generation.

Abstract

Two-color lasers with high coherence are paramount in precision measurement, accurate light-matter interaction, and low-noise photonic microwave generation. However, conventional two-color lasers often suffer from low coherence, particularly when these two colors face large frequency spacings. Here, harnessing the Pound-Drever-Hall technique, we synchronize two lasers to a shared ultra-stable optical reference cavity to break through the thermal noise constraint, achieving a highly coherent two-color laser. With conquering these non-common mode noises, we demonstrate an exceptional fractional frequency instability of 2.7E-17 at 1 second when normalized to the optical frequency. Characterizing coherence across large frequency spacings poses a significant challenge. To tackle this, we employ electro-optical frequency division to transfer the relative stability of a 0.5 THz spacing two-color laser to a 25 GHz microwave signal. As its performance surpasses the sensitivity of the current apparatus, we establish two independent systems for comparative analyses. The resulting 25 GHz signals exhibit exceptional phase noise of -74 dBc/Hz at 1 Hz and -120 dBc/Hz at 100 Hz, demonstrating the two-color laser's performance approaching the quantum noise limit of its synchronization system. It also sets a new record for the two-point frequency division method in photonic microwave generation. Our achievement in highly coherent two-color lasers and low-noise microwave signals will usher in a new era for precision measurements and refine the accuracy of light-matter and microwave-matter interactions to their next decimal place.