Enhanced bandwidth in radiation sensors operating at the fundamental temperature fluctuation noise limit

TL;DR

This paper demonstrates that radiation sensors operating at their fundamental temperature fluctuation noise limit can achieve bandwidths much larger than traditional thermal response constraints, using nanomechanical sensors with stable frequency tracking.

Contribution

The study introduces a method to surpass traditional bandwidth limits in radiation sensors by leveraging fundamental temperature fluctuation noise in nanomechanical sensors with closed-loop frequency stabilization.

Findings

Achieved a 54 Hz bandwidth in temperature fluctuation noise-limited sensors.

Maintained near-peak detectivity within a factor of 3 across the extended bandwidth.

Derived and experimentally validated a predictive model for bandwidth enhancement.

Abstract

Temperature-based radiation detectors are an essential tool for long optical wavelengths detection even if they often suffer from important bandwidth limitations. Their responsivity, and hence their noise equivalent power (NEP), typically degrade at frequencies exceeding the cutoff set by their characteristic thermal response time ($\tau_\text{th}$), i.e., at $\omega > \tau_\text{th}^{-1}$. Here we show that this bandwidth limitation can be broken when a radiation 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 $\text{Hz}$. In this range, the sensor performance remains within a factor 3 from its peak detectivity ($D_T^* = 7.4 \times 10^9~\mathrm{cm \cdot Hz^{1/2} W^{-1}}$) even though the thermal cutoff frequency is 30 times lower (i.e., $1/2\mathrm{\pi} \tau_\text{th} = 1.8~\text{Hz}$). We also derive and validate experimentally closed-form expression predicting maximum bandwidth enhancement in the context of nanomechanical resonators interfaced with a closed-loop frequency tracking scheme.