Characterization of a photonic crystal mirror for quantum optomechanics

The ability to control nanomechanical devices using radiation pressure is the foundation for quantum optomechanical technologies. We have fabricated Si3N4 membranes with embedded photonic crystal (PtC) reflectors to enhance their susceptibility to radiation pressure at near-infrared wavelengths. In this poster we present efforts to characterize the optical properties of the PtC-etched Si3N4 membrane with sub-100 nm thickness, with the objective of achieving 99% reflectivity at a wavelength of 850 nm. Characterizations were made by measuring the reflectance across a broad spectrum of wavelengths using a tunable Titanium-Sapphire laser and a custom reflectometer employing a quadriaxial sample mount. Unpatterned 90 nm thick Si3N4 membranes were found to reflect ~35% of light at 850 nm. PtC membranes with the same thickness were found to have a reflectance of ~90% at 861 nm, for an incident beam with a spot size of 100 µm. These results are consistent with previous sub-100-nm-thick PtC reflectors at near-infrared wavelengths, suggesting the need for thicker membranes. Ultimately, the PtC mirror will be integrated into an optical microcavity as a platform for quantum-limited force sensing and electro-optic conversion applications.