Angular momentum dynamics of light-driven mass density waves in thin film structures

We have recently developed the mass-polariton (MP) theory of light to describe propagation of light in dielectric materials [Phys. Rev. A 95, 063850 (2017)]. The MP theory considers a light wave simultaneously with the dynamics of the medium atoms driven by optoelastic forces between the field-induced dipoles and the electromagnetic field. The MP theory combines the well-known optical forces with the Newtonian dynamics of the medium. Therefore, it can be applied to any inhomogeneous, dispersive, and lossy materials. One of the key observations of the MP theory of light is that a light pulse propagating in a nondispersive dielectric transfers an increased atomic density such that the total transferred mass is equal to δM = (n ² - 1)E/c ² , where n is the refractive index and E is the electromagnetic energy of the pulse. This mass is transferred by an atomic mass density wave (MDW) where the atoms are spaced more densely inside the light pulse as a result of the optical force. Another key observation is that, in common semiconductors, most of the linear and angular momenta of light is transferred by the semiconductor atoms in the MDW moving under the influence of the optical force. In this work, we use the electric and magnetic fields of selected Laguerre-Gaussian mode beams to calculate the optical force density, which is used in the optoelastic continuum dynamics to simulate the dynamics of medium atoms in edge-supported free-standing thin film structures. The goal of our work is to find out how the different force components related to the reflection, transmission, absorption, and the atomic MDW bend and twist the film. The simulations also aim at optimizing experimental studies of the atomic dynamics in the thin film and to relating the measurements to the properties of incoming light.