A high stability semiconductor laser system for a $^{88}$Sr-based optical lattice clock

TL;DR

This paper presents a highly stable 698 nm diode laser system for strontium optical lattice clocks, achieving ultra-low noise, remote high-resolution spectroscopy, and environmental robustness for potential transportable applications.

Contribution

It introduces a state-of-the-art frequency stabilized laser system with low thermal noise and demonstrates high-resolution remote spectroscopy over a fiber link, advancing optical clock technology.

Findings

Laser frequency noise is about three times the thermal noise limit between 2-11 Hz.

Achieved a frequency stability of 7×10^{-18} over 100 seconds via fiber link.

Environmental disturbances impact the laser system's stability, relevant for transportable clocks.

Abstract

We describe a frequency stabilized diode laser at 698 nm used for high resolution spectroscopy of the 1S0-3P0 strontium clock transition. For the laser stabilization we use state-of-the-art symmetrically suspended optical cavities optimized for very low thermal noise at room temperature. Two-stage frequency stabilization to high finesse optical cavities results in measured laser frequency noise about a factor of three above the cavity thermal noise between 2 Hz and 11 Hz. With this system, we demonstrate high resolution remote spectroscopy on the 88Sr clock transition by transferring the laser output over a phase-noise-compensated 200 m-long fiber link between two separated laboratories. Our dedicated fiber link ensures a transfer of the optical carrier with frequency stability of 7 \cdot 10^{-18} after 100 s integration time, which could enable the observation of the strontium clock transition with an atomic Q of 10^{14}. Furthermore, with an eye towards the development of transportable optical clocks, we investigate how the complete laser system (laser+optics+cavity) can be influenced by environmental disturbances in terms of both short- and long-term frequency stability.