On the Modified Einstein-Laub and Modified Chu Optical Force Formulations

TL;DR

This paper investigates discrepancies among optical force formulations, proposing modified Einstein-Laub and Chu models that align with experiments, and discusses their physical consistency and potential for future experimental validation.

Contribution

It introduces modified optical force formulations derived from mathematical consistency conditions that better match experimental results and explores their physical implications.

Findings

Modified Einstein-Laub and Chu formulations agree with experimental data.

Distinct formulations predict non-zero bulk force in lossless objects.

Proposes experiments to test the physical validity of these formulations.

Abstract

In several experiments involving material background, it has been observed that the Chu, Einstein-Laub and Ampere formulations of optical force lead to either different optical forces or wrong total optical force. In order to identify the exact reason behind such significant disagreements, we investigate the optical force in a number of tractor beam and lateral force experiments. We demonstrate that the modified Einstein-Laub or modified Chu formulations, obtained from two mathematical consistency conditions of force calculation, give the time-averaged force that agrees with the experiments. We consider both the chiral and achiral objects embedded in complex material backgrounds. Though the distinct formulations of optical force have been made mathematically equivalent in this work; the aspect of physical consistency of these distinct optical force formulations have also been investigated. It is known that the theory of Minkowski suggests zero bulk force inside a lossless object for which we still do not have any experimental verification. In contrast, both modified Einstein-Laub and modified Chu force formulations suggest non-zero bulk force inside a lossless object. Hence, for a future resolution of this discrepancy, we also suggest a possible experiment to investigate the bulk force and to check the validity of these distinct formulations.