Material absorption is a key limitation in nanophotonic systems; however, its characterization is often obscured by scattering and diffraction. Here we show that nanomechanical frequency spectroscopy can be used to characterize material absorption at the parts per million level and use it to characterize the extinction coefficient κ of stoichiometric silicon nitride (Si₃N₄). Specifically, we track the frequency shift of a high-Q Si₃N₄ trampoline in response to laser photothermal heating and infer κ from a model including stress relaxation and both conductive and radiative heat transfer. A key insight is the presence of two thermalization time scales: rapid radiative cooling of the Si₃N₄ film and slow parasitic heating of the Si chip. We infer κ ∼ 0.1–1 ppm for Si₃N₄ in the 532–1550 nm wavelength range, matching bounds set by waveguide resonators. Our approach is applicable to diverse photonic materials and may offer new insights into their potential.

中文翻译：

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氮化硅的亚 ppm 纳米机械吸收光谱

材料吸收是纳米光子系统的一个关键限制；然而，它的特征常常被散射和衍射所掩盖。在这里，我们表明纳米机械频谱可用于表征百万分之一级别的材料吸收，并用它来表征化学计量氮化硅（Si ₃ N ₄）的消光系数κ。具体来说，我们跟踪高Q Si ₃ N ₄蹦床响应激光光热加热的频移，并从包括应力松弛以及传导和辐射传热的模型推断 κ。一个关键的见解是存在两个热化时间尺度：Si ₃ N ₄薄膜的快速辐射冷却和Si芯片的缓慢寄生加热。我们推断 Si ₃ N ₄在 532–1550 nm 波长范围内的 κ ∼ 0.1–1 ppm，与波导谐振器设定的范围相匹配。我们的方法适用于各种光子材料，并可能为它们的潜力提供新的见解。