Optical forces arising from phase gradients

TL;DR

This paper explores how phase gradients in light fields generate forces on objects, including transverse forces, and discusses their non-conservative nature and implications.

Contribution

It introduces the concept that phase gradients can produce forces on objects, extending the understanding of optical forces beyond traditional radiation pressure.

Findings

Phase gradients exert measurable forces on illuminated objects.

Transverse forces can be generated by phase gradients.

These forces generally violate conservation of energy.

Abstract

We demonstrate both theoretically and experimentally that gradients in the phase of a light field exert forces on illuminated objects, including forces transverse to the direction of propagation. This effect generalizes the notion of the photon orbital angular momentum carried by helical beams of light. We further demonstrate that these forces generally violate conservation of energy, and briefly discuss some ramifications of their non-conservativity.