Laser interferometry with translucent and absorbing mechanical oscillators

TL;DR

This paper demonstrates that a Michelson-Sagnac interferometer with a translucent silicon nitride membrane can operate effectively for quantum opto-mechanical experiments, maintaining high quality factors and low absorption at room temperature.

Contribution

It provides an experimental analysis showing optimal conditions for quantum experiments using translucent oscillators in a Michelson-Sagnac interferometer.

Findings

Silicon nitride membranes can be coupled to high laser powers without quality degradation.

Interferometer configuration allows minimal absorption and noise rejection.

Experimental data confirms theoretical models of optical and mechanical behavior.

Abstract

The sensitivity of laser interferometers can be pushed into regimes that enable the direct observation of quantum behaviour of mechanical oscillators. In the past, membranes with subwavelength thickness (thin films) have been proposed as high-mechanical-quality, low-thermal-noise oscillators. Thin films from a homogenous material, however, generally show considerable light transmission accompanied by heating due to light absorption, which typically reduces the mechanical quality and limits quantum opto-mechanical experiments in particular at low temperatures. In this work, we experimentally analyze a Michelson-Sagnac interferometer including a translucent silicon nitride (SiN) membrane with subwavelength thickness. We find that such an interferometer provides an operational point being optimally suited for quantum opto-mechanical experiments with translucent oscillators. In case of a balanced beam splitter of the interferometer, the membrane can be placed at a node of the electro-magnetic field, which simultaneously provides lowest absorption and optimum laser noise rejection at the signal port. We compare the optical and mechanical model of our interferometer with experimental data and confirm that the SiN membrane can be coupled to a laser power of the order of one Watt at 1064 nm without significantly degrading the membrane's quality factor of the order 10^6, at room temperature.