Thermal noise and optomechanical features in the emission of a membrane-coupled compound cavity laser diode

TL;DR

This paper demonstrates a cost-effective, high-sensitivity optical displacement detector using a membrane-coupled laser diode cavity, capable of measuring thermal motion at room temperature and opening new avenues in quantum optomechanics.

Contribution

It introduces a novel compound cavity system with high Q-factor for detecting thermal motion, combining laser and membrane dynamics for optomechanical applications.

Findings

High Q-factor (~3.4×10^4) at 73 kHz enables room-temperature thermal motion detection.

The system can measure membrane vibrations with ~87 pm RMS sensitivity.

Potential for exploring non-Markovian quantum effects at mesoscale.

Abstract

We demonstrate the use of a compound optical cavity as linear displacement detector, by measuring the thermal motion of a silicon nitride suspended membrane acting as the external mirror of a near-infrared Littrow laser diode. Fluctuations in the laser optical power induced by the membrane vibrations are collected by a photodiode integrated within the laser, and then measured with a spectrum analyzer. The dynamics of the membrane driven by a piezoelectric actuator is investigated as a function of air pressure and actuator displacement in a homodyne configuration. The high Q-factor ($\sim 3.4\cdot 10^4$ at $8.3 \cdot 10^{-3}$ mbar) of the fundamental mechanical mode at $\sim 73$ kHz guarantees a detection sensitivity high enough for direct measurement of thermal motion at room temperature ($\sim 87$ pm RMS). The compound cavity system here introduced can be employed as a table-top, cost-effective linear displacement detector for cavity optomechanics. Furthermore, thanks to the strong optical nonlinearities of the laser compound cavity, these systems open new perspectives in the study of non-Markovian quantum properties at the mesoscale.