Enhanced Bandwidth in Radiation Sensors Operating at the Fundamental Temperature Fluctuation Noise Limit

Temperature-based radiation detectors are essential for long-wavelength detection, but they suffer from important bandwidth limitations. Their responsivity and, hence, their noise equivalent power (NEP) typically degrade at frequencies exceeding their characteristic thermal response time cutoff (τth), i.e., at ω > τth–1. We show that this bandwidth limitation can be broken when a sensor operates at its fundamental temperature fluctuation noise limit. The key enabler of this demonstration is a nanomechanical sensor in which frequency stability is limited by fundamental temperature fluctuations over an unprecedentedly large bandwidth of 54 Hz. In this range, the sensor performance remains within a factor 3 of its peak detectivity (DT* = 7.4 × 109 cm Hz1/2 W–1) even though the thermal cutoff frequency is 30 times lower (i.e., 1/2πτth = 1.8 Hz). We also derive expressions predicting this bandwidth enhancement for nanomechanical resonator-based sensors within a closed-loop frequency tracking scheme.