Micro-scale opto-thermo-mechanical actuation in the dry adhesive regime

TL;DR

This paper introduces a novel opto-thermo-mechanical method to actuate microscopic objects on dry surfaces using pulsed laser-induced thermoelastic waves, overcoming strong surface adhesion forces.

Contribution

It establishes a general principle linking friction and thermoelastic waves for micro-object actuation, supported by theoretical predictions and experimental demonstrations.

Findings

Nanosecond pulsed laser can control micro-scale frictional motion.

Gold plates exhibit spiral motion driven by pulsed laser.

Motion control rules for micro-objects are identified.

Abstract

Realizing optical manipulation of microscopic objects is crucial in the research fields of life science, condensed matter physics and physical chemistry. In non-liquid environments, this task is commonly regarded as difficult due to strong adhesive surface force ($\sim\mu\rm N$) between solid interfaces that makes tiny optical driven force ($\sim\rm pN$) insignificant. Here, by recognizing the microscopic interaction mechanism between friction force -- the parallel component of surface force on the contact surface -- and thermoelastic waves induced by pulsed optical absorption, we establish a general principle enabling the actuation of micro-objects on dry frictional surfaces based on the opto-thermo-mechanical effects. Theoretically, we predict that nanosecond pulsed optical absorption with mW-scale peak power is sufficient to tame $\mu\rm N$-scale friction force. Experimentally, we demonstrate that two-dimensional spiral motion of gold plates on micro-fibers driven by a nanosecond pulsed laser, and reveal the specific rules of motion control. Our results pave the way for future development of micro-scale actuators in nonliquid environments.