Non-linear bistability in pulsed optical traps

TL;DR

This paper explores non-linear bistability in pulsed optical traps, revealing feedback effects between particle permittivity and internal fields that lead to hysteresis, with implications for nanoparticle manipulation and novel states like time crystals.

Contribution

It introduces a new formalism accounting for feedback between permittivity and internal fields, advancing understanding of optical bistability in pulsed traps.

Findings

Demonstrates hysteresis effects in pulsed optical traps

Develops a formalism considering feedback between permittivity and internal fields

Highlights potential applications in nanoparticle manipulation and time crystals

Abstract

Optical trapping, also known as optical tweezing or optical levitation, is a technique that uses highly focused laser beams to manipulate micro- and nanoscopic particles. In optical traps driven by high-energy pulses, material non-linearity can result in unusual opto-mechanical effects, such as displaced equilibrium points. However, existing theoretical models of non-linear optical force on small particles consider smooth material dependence on the incident field strength alone, and not the feedback between the particle permittivity and internal field strength, which is, in turn, a function of the permittivity. The hysteresis effects of optical bistability in pulsed optical traps therefore elude existing optical force models. Here, we investigate a bistable optical trap, set up by counter-propagating ultrashort pulses, in which the optical force exerted on a particle depends not only on the field at the particle's current location, but on the particle's historic trajectory in the trap. The developed formalism will be important for designing optical traps and nanoparticle manipulation in pulsed field for various applications, including potentially time crystal demonstrations.