Optical Forces of Focused Ultrafast Laser Pulses on Nonlinear Optical Rayleigh Particles

TL;DR

This paper develops a theoretical framework to analyze optical forces on nonlinear optical nanoparticles trapped by ultrafast laser pulses, highlighting how nonlinear effects influence trapping stability and potential well structure.

Contribution

It introduces a model for time-averaged optical forces considering nonlinear polarization effects in ultrafast laser trapping of nanoparticles.

Findings

Self-focusing enhances trapping stability.

Self-defocusing causes potential well splitting.

Model aligns with experimental observations.

Abstract

The principle of optical trapping is conventionally based on the interaction of optical fields with linear induced polarizations. However, the optical force originating from the nonlinear polarization becomes significant when nonlinear optical nanoparticles are trapped by ultrafast laser pulses. Herein we establish the time-averaged optical forces on a nonlinear optical nanoparticle using high-repetition-rate ultrafast laser pulses, based on the linear and nonlinear polarization effects. We investigate the dependence of the optical forces on the magnitudes and signs of the refractive nonlinearities. It is found that the self-focusing effect enhances the trapping ability, whereas the self-defocusing effect leads to the splitting of potential well at the focal plane and destabilizes the optical trap. Our results show good agreement with the reported experimental observations and provide a theoretical support for capturing nonlinear optical particles.