Sub-ppm Nanomechanical Absorption Spectroscopy of Silicon Nitride

Abstract

Material absorption is a key limitation in nanophotonic systems; however, its characterization is often obscured by scattering and diffraction loss. Here we show that nanomechanical frequency spectroscopy can be used to characterize the absorption of a dielectric thin film at the parts-per-million (ppm) level, and use it to characterize the absorption of stoichiometric silicon nitride (Si${}_3$N${}_4$), a ubiquitous low-loss optomechanical material. Specifically, we track the frequency shift of a high-$Q$ Si${}_3$N${}_4$ trampoline resonator in response to photothermal heating by a $\sim 10$ mW laser beam, and infer the absorption of the thin film from a model including thermal stress relaxation and both radiative and conductive heat transfer. A key insight is the presence of two thermalization timescales, a rapid ($\sim 0.1$ sec) timescale due to radiative thermalization of the Si${}_3$N${}_4$ thin film, and a slow ($\sim 100$ sec) timescale due to parasitic heating of the Si device chip. We infer the extinction coefficient of Si${}_3$N${}_4$ to be $\sim 0.1-1$ ppm in the 532 - 1550 nm wavelength range, comparable to bounds set by waveguide resonators and notably lower than estimates with membrane-in-the-middle cavity optomechanical systems. Our approach is applicable to a broad variety of nanophotonic materials and may offer new insights into their potential.

References in corpus (12)

• Dispersive optomechanics: a membrane inside a cavity
• High quality mechanical and optical properties of commercial silicon nitride membranes
• Ultra-Low-Loss Silicon Nitride Photonics Based on Deposited Films Compatible with Foundries
• Room-Temperature Sputtered Ultralow-loss Silicon Nitride for Hybrid Photonic Integration
• High-Strength Amorphous Silicon Carbide for Nanomechanics
• Tensile strained $I{n}_{x}G{a}_{1-x}P$ membranes for cavity optomechanics
• Thermal radiation dominated heat transfer in nanomechanical silicon nitride drum resonators
• Towards cavity-free ground state cooling of an acoustic-frequency silicon nitride membrane
• Determining Young's modulus via the eigenmode spectrum of a nanomechanical string resonator
• Nanomechanical spectroscopy of 2D materials
• Demonstration of Frequency Stability limited by Thermal Fluctuation Noise in Silicon Nitride Nanomechanical Resonators
• Nanomechanical Photothermal Near Infrared Spectromicroscopy of Individual Nanorods

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• On-Chip Frequency Noise Cancellation in Nanomechanical Resonators using Cavity Optomechanics
• Optomechanical Accelerometer Search for Ultralight Dark Matter