D. E. Edmundson and R. H. Enns, "The particle-like nature of colliding light bullets," Physical Review A. 51, 2491 (1995).

Numerical scattering experiments in a medium characterized by a simple saturable refractive index demonstrate the particle-like behaviour of 3-dimensional bright optical envelope solitons (`light bullets') for the situation where the colliding bullets initially have a $\pi$-phase difference and are on the positive-slope branch of the energy curve. By varying the initial bullet velocities, bullet energy content, and the impact parameter, the nature of the repulsive interaction potential (i.e. the force law) is ascertained to be a Yukawa potential whose decay constant agrees quite well with that obtained by assuming that each light bullet sees only the `tail' of the other bullet. The scattering data scale correctly with velocity and one finds that the bullet energy is the natural analog of particle mass.