Thermal magnetic field noise: Electron optics and decoherence

Thermal magnetic field noise from magnetic and non-magnetic conductive parts close to the electron beam recently has been identified as a reason for decoherence in high-resolution transmission electron microscopy (TEM). Here, we report about new experimental results from measurements for a layered structure of magnetic and non-magnetic materials. For a simplified version of this setup and other situations we derive semi-analytical models in order to predict the strength, bandwidth and spatial correlation of the noise fields. The results of the simulations are finally compared to previous and new experimental data in a quantitative manner. •We report on magnetic field noise of a thermodynamic origin which can cause decoherence in the medium voltage electron microscope (S)TEM.•Previously published and new experimental results are compared to theoretical predictions.•Layered structures of non-magnetic and magnetic materials in electron-optical components are treated theoretically and covered by experiments.•Various ways to calculate the power spectral density of the magnetic noise based on the fluctuation-dissipation theorem are used for the evaluation.•The calculated spatial coherence of magnetic noise in a beam tube is used for the comparison of theoretical predictions and experiments.