Position-dependent calibration and frequency stability in on-axis optical transduction of vertical InP nanowire resonators

Abstract

We present a quantitative framework for on-axis optical transduction of vertical InP nanowire resonators, correlating laser position to signal amplitude, calibration, and frequency stability. Photothermal resonance detuning is used to reconstruct the local beam intensity profile and to calibrate the photodetector signal using the thermomechanical noise. A noise model incorporating shot noise and spatial variation in substrate reflectance predicts the position-dependent Allan deviation. We find that the optimal detection position lies near the steepest intensity gradient, and that increasing laser power does not significantly improve frequency stability, because the accompanying temperature rise enhances thermomechanical noise and offsets the signal gain. These results establish design guidelines for optimizing nanowire-based sensors in on-axis optical detection schemes.