Phase noise measurement of external cavity diode lasers and implications for optomechanical sideband cooling of GHz mechanical modes

TL;DR

This paper measures the phase noise of external cavity diode lasers used in optomechanical experiments, revealing significant excess noise at GHz frequencies that can hinder ground-state cooling of mechanical oscillators.

Contribution

It provides the first detailed characterization of phase noise in widely used tunable diode lasers at GHz frequencies, highlighting limitations for quantum optomechanics.

Findings

Peak phase noise around 10^7 rad^2/Hz near 3.5 GHz

Diode lasers do not reach quantum-limited performance at GHz frequencies

Excess noise can prevent ground-state cooling in nano-optomechanical systems

Abstract

Cavity opto-mechanical cooling via radiation pressure dynamical backaction enables ground state cooling of mechanical oscillators, provided the laser exhibits sufficiently low phase noise. Here, we investigate and measure the excess phase noise of widely tunable external cavity diode lasers, which have been used in a range of recent nano-optomechanical experiments, including ground-state cooling. We report significant excess frequency noise, with peak values on the order of 10^7 rad^2 Hz near 3.5 GHz, attributed to the diode lasers' relaxation oscillations. The measurements reveal that even at GHz frequencies diode lasers do not exhibit quantum limited performance. The associated excess backaction can preclude ground-state cooling even in state-of-the-art nano-optomechanical systems.