Design of an experimental setup for the measurement of light-driven atomic mass density waves in a silicon crystal

The recently introduced mass-polariton (MP) theory of light describes light in a medium as a coupled state of the field and matter [Phys. Rev. A 95, 063850 (2017)]. In the MP theory, the optical force density drives forward an atomic mass density wave (MDW) that accompanies electromagnetic waves in a medium. The MDW is necessary for the fulfilment of the conservation laws and the Lorentz covariance of light. In silicon at wavelength λ0 = 1550 nm, the atomic MDW carries 92% of the total momentum and angular momentum of light. The MDW of a light pulse having field energy E propagating in a dielectric also transfers a net mass equal to δM = (npng − 1)E/c2 , where np and ng are the phase and group refractive indices. In this work, we present a schematic experimental setup for the measurement of the MDW in a silicon crystal. This setup overcomes many challenges that have been present in previously introduced setups and that have made the experimental observation of the MDW effect difficult due to its smallness in comparison with other effects, such as the momentum transfer by absorption and reflections. The present setup also overcomes challenges with elastic relaxation effects while extending possible measurement time scales beyond the time scale of sound waves in the setup geometry. For the proposed setup, we also compare the predictions of the MP theory of light to the predictions of the conventional Minkowski theory, where the total momentum of light is carried by the electromagnetic field. We also aim at optimizing experimental studies of the MDW effect using the proposed setup.