Towards Stirling engine using an optically confined particle subjected to asymmetric temperature profile

TL;DR

This paper demonstrates a microscopic Stirling engine using a lanthanide-doped particle manipulated by optical trapping and wavelength-dependent activity regulation, harnessing asymmetric temperature profiles for work cycles.

Contribution

It introduces a novel optical setup to control particle activity via wavelength tuning, enabling the realization of a microscopic Stirling engine with stochastic work estimation.

Findings

Particle activity depends on trapping wavelength, enabling cycle control.

The system can perform multiple Stirling engine cycles.

Statistical work estimation over cycles demonstrates engine feasibility.

Abstract

The realization of microscopic heat engines has gained a surge of research interest in statistical physics, soft matter, and biological physics. A typical microscopic heat engine employs a colloidal particle trapped in a confining potential, which is modulated in time to mimic the cycle operations. Here, we use a lanthanide-doped upconverting particle (UCP) suspended in a passive aqueous bath, which is highly absorptive at 975 nm and converts NIR photons to visible, as the working substance of the engine. When a single UCP is optically trapped with a 975 nm laser, it behaves like an active particle by executing motion subjected to an asymmetric temperature profile along the direction of propagation of the laser. The strong absorption of 975 nm light by the particle introduces a temperature gradient and results in significant thermophoretic diffusion along the temperature gradient. However, the activity of the particle vanishes when the trapping wavelength is switched to 1064 nm. We carefully regulate the wavelength-dependent activity of the particle to engineer all four cycles of a Stirling engine by using a combination of 1064 nm and 975 nm wavelengths. Since the motion of the particle is stochastic, the work done on the particle due to the stiffness modulation per cycle is random. We provide statistical estimation for this work averaged over 5 cycles which can be extended towards several cycles to make a Stirling engine. Our experiment proposes a robust set-up to systematically harness temperature which is a crucial factor behind building microscopic engines.