Measuring and engineering the atomic mass density wave of a Gaussian mass-polariton pulse in optical fibers

TL;DR

This paper extends the mass-polariton theory of light to dispersive media, demonstrating how intense Gaussian pulses in silicon fibers transfer mass via atomic density waves, enabling novel high-frequency device concepts.

Contribution

It generalizes the covariant mass-polariton theory to dispersive media and explores experimental measurement of mass transfer in silicon fibers with Gaussian pulses.

Findings

Most light momentum in semiconductors is transferred by moving atoms.

Mass density waves propagate with the speed of light, not sound.

Potential for high-frequency mechanical oscillators based on MDWs.

Abstract

Conventional theories of electromagnetic waves in a medium assume that only the energy of the field propagates inside the medium. Consequently, they neglect the transport of mass density by the medium atoms. We have recently presented foundations of a covariant theory of light propagation in a nondispersive medium by considering a light wave simultaneously with the dynamics of the medium atoms driven by optoelastic forces [Phys. Rev. A 95, 063850 (2017)]. In particular, we have shown that the mass is transferred by an atomic mass density wave (MDW), which gives rise to mass-polariton (MP) quasiparticles, i.e., covariant coupled states of the field and matter having a nonzero rest mass. Another key observation of the mass-polariton theory of light is that, in common semiconductors, most of the momentum of light is transferred by moving atoms, e.g., 92% in the case of silicon. In this work, we generalize the MP theory of light for dispersive media and consider experimental measurement of the mass transferred by the MDW atoms when an intense light pulse propagates in a silicon fiber. In particular, we consider optimal intensity and time dependence of a Gaussian pulse and account for the breakdown threshold irradiance of the material. The optical shock wave property of the MDW, which propagates with the velocity of light instead of the velocity of sound, prompts for engineering of novel device concepts like very high frequency mechanical oscillators not limited by the acoustic cutoff frequency.