Nanokelvin-Resolution Micro-Thermometry at Room Temperature

Ultrahigh-resolution thermometry is critical for sensitive bolometry for infrared (IR) and terahertz (THz) detection and imaging as well as sensitive calorimetry for probing dissipation in electronic, optoelectronic and quantum devices. In spite of recent advances in the field, achieving high-resolution measurements from microscale devices at room temperature remains an outstanding challenge. Here, we present a photonic thermometer with optical readout – called the Band-Edge Thermometer (BET) – that achieves this goal by relying on the strong, temperature-dependent optical properties of GaAs at its band edge. Specifically, using a suspended asymmetric Fabry–Pérot resonator and a narrow-linewidth probe laser we demonstrate a thermoreflectance coefficient of >30 K⁻¹, enabling thermometry with a noise floor of ~60 nK Hz^−1/2 and a resolution of <100 nK in a bandwidth of 0.1 Hz. The advances presented here are expected to enable a broad range of studies and applications in calorimetry and bolometry where miniaturized high-resolution thermometers are required.