Laser-induced heating for the experimental study of critical Casimir forces with optical trapping

TL;DR

This study uses laser-induced heating to control critical Casimir forces between colloidal particles, enabling analysis of non-equilibrium energetics and fluctuation theorems in a tunable, bath-induced force system.

Contribution

It introduces a novel experimental approach to modulate Casimir forces via laser heating and applies fluctuation theorems to analyze non-equilibrium energetics in this context.

Findings

Controlled Casimir interactions through laser heating.

Quantified work dissipation and free energy storage.

Demonstrated non-equilibrium behavior in critical colloidal systems.

Abstract

Critical Casimir interactions represent a perfect example of bath-induced forces at mesoscales. These forces may have a relevant role in the living systems as well as a role in the design of nanomachines fueled by environmental fluctuations. Since the thermal fluctuations are enhanced in the vicinity of a demixing point of a second-order phase transition, we can modulate the magnitude and range of these Casimir-like forces by slight changes in the temperature. Here, we consider two optical trapped colloidal beads inside a binary mixture. The Casimir interaction is controlled by warming the mixture by laser-induced heating, whose local application ensures high reproducibility. Once this two-particle system is warmed, the critical behavior of different observables allows the system to become its self-thermometer. We use this experimental scheme for analyzing the energetics of a critical colloidal system under a non-equilibrium-driven protocol. We quantify how the injected work can be dissipated to the environment as heat or stored as free energy. Indeed, our system allows us to use the fluctuation theorems framework for analyzing the performance of this critically driven toy model. Our work paves the way for future experimental studies on the non-equilibrium features of bath-induced forces and the design of critically driven nanosystems.