Detection of the Abraham force with a succession of short optical pulses

TL;DR

This paper proposes an experimental setup using short optical pulses in a fiber to directly measure the Abraham force, aiming to distinguish it from Minkowski's prediction, which has remained experimentally elusive for over a century.

Contribution

It introduces a novel optical experiment to measure the Abraham force directly, providing a feasible method to differentiate between Abraham and Minkowski energy-momentum tensors at optical frequencies.

Findings

Predicted torque is detectable with standard laser and torsion pendulum setup.

The Abraham and Minkowski tensors predict opposite signs for the torque.

Angular deflection of about 10^{-3} radians is achievable and visible.

Abstract

For over a century, two rival descriptions of electromagnetic field momentum in matter have co-existed, due to Abraham and Minkowski, respectively. We propose a set-up for measuring the difference between Abraham's and Minkowski's predictions in optics. To wit, a set-up is proposed in which the transient "Abraham force", a consequence of the Abraham energy-momentum tensor of 1909 may be measured directly. We show that when a train of short laser pulses is sent through a fiber wound up on a cylindrical drum, the Abraham theory predicts a torque which, by inserting realistic parameters, is found to be detectable. Indeed, the same torque when calculated with the Minkowski tensor takes the opposite sign. Numerical estimates show that with a typical torsion pendulum set-up and standard laser parameters, the angular deflection is in the order of $10^{-3}$ rad, which is easily measurable and even visible to the naked eye. Although its prediction is a century old, the Abraham force has proven experimentally elusive, and to our knowledge no macroscopic experimental demonstration of the difference between the predictions of the two mentioned energy-momentum tensors exists at optical frequencies.