Mechanical mode dependence of bolometric back-action in an AFM microlever

TL;DR

This study investigates how photothermal back-action in an AFM microlever affects different vibration modes, revealing mode-dependent behaviors including simultaneous damping and amplification, influenced by laser spot position.

Contribution

It demonstrates for the first time that photothermal back-action can act oppositely on different modes of a microlever, depending on laser spot position and mode shape.

Findings

Photothermal back-action can amplify one mode while damping another.

Mode behavior depends on laser spot position relative to mode shape.

Experimental results confirm mode-dependent back-action effects.

Abstract

Two back action (BA) processes generated by an optical cavity based detection device can deeply transform the dynamical behavior of an AFM microlever: the photothermal force or the radiation pressure. Whereas noise damping or amplifying depends on optical cavity response for radiation pressure BA, we present experimental results carried out under vacuum and at room temperature on the photothermal BA process which appears to be more complex. We show for the first time that it can simultaneously act on two vibration modes in opposite direction: noise on one mode is amplified whereas it is damped on another mode. Basic modeling of photothermal BA shows that dynamical effect on mechanical mode is laser spot position dependent with respect to mode shape. This analysis accounts for opposite behaviors of different modes as observed.