Sub-ppm Nanomechanical Absorption Spectroscopy of Silicon Nitride
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arXiv
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| Format: | Preprint |
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2023
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| _version_ | 1866911876394254336 |
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| author | Land, Andrew T. Chowdhury, Mitul Dey Agrawal, Aman R. Wilson, Dalziel J. |
| author_facet | Land, Andrew T. Chowdhury, Mitul Dey Agrawal, Aman R. Wilson, Dalziel J. |
| contents | 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 $\sim10$ 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 ($\sim0.1$ sec) timescale due to radiative thermalization of the Si$_3$N$_4$ thin film, and a slow ($\sim100$ sec) timescale due to parasitic heating of the Si device chip. We infer the extinction coefficient of Si$_3$N$_4$ to be $\sim0.1-1$ 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2312_05249 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Sub-ppm Nanomechanical Absorption Spectroscopy of Silicon Nitride Land, Andrew T. Chowdhury, Mitul Dey Agrawal, Aman R. Wilson, Dalziel J. Optics Mesoscale and Nanoscale Physics Applied Physics Instrumentation and Detectors 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 $\sim10$ 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 ($\sim0.1$ sec) timescale due to radiative thermalization of the Si$_3$N$_4$ thin film, and a slow ($\sim100$ sec) timescale due to parasitic heating of the Si device chip. We infer the extinction coefficient of Si$_3$N$_4$ to be $\sim0.1-1$ 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. |
| title | Sub-ppm Nanomechanical Absorption Spectroscopy of Silicon Nitride |
| topic | Optics Mesoscale and Nanoscale Physics Applied Physics Instrumentation and Detectors |
| url | https://arxiv.org/abs/2312.05249 |