Influence of random roughness on the Casimir force at small separations

TL;DR

This study investigates how random surface roughness of gold films affects the Casimir force at small separations, revealing significant deviations from theoretical models below 100 nm.

Contribution

It provides experimental data and analysis on the impact of surface roughness on the Casimir force, highlighting limitations of perturbation theory at very small separations.

Findings

Roughness causes strong deviations below 100 nm

Deviations from theory can exceed 100%

Experimental measurements align with theoretical predictions at larger separations

Abstract

The influence of random surface roughness of Au films on the Casimir force is explored with atomic force microscopy in the plate-sphere geometry. The experimental results are compared to theoretical predictions for separations ranging between 20 and 200 nm. The optical response and roughness of the Au films were measured and used as input in theoretical predictions. It is found that at separations below 100 nm, the roughness effect is manifested through a strong deviation from the normal scaling of the force with separation distance. Moreover, deviations from theoretical predictions based on perturbation theory can be larger than 100%.