A quantum cascade phonon-polariton laser

TL;DR

This paper introduces a novel quantum cascade laser that emits phonon-polaritons at terahertz frequencies, demonstrating coherent coupling between photons and phonons with low temperature dependence and operation in ultra-thin cavities.

Contribution

It reports the first phonon-polariton laser based on a quantum cascade structure, with detailed analysis of polariton composition and gain mechanisms.

Findings

Achieved emission at 10.4 THz frequency.

Maximum phonon fraction of 50% in polaritons.

Low temperature dependence of threshold current.

Abstract

We report a laser that coherently emits phonon-polaritons, quasi-particles arising from the coupling between photons and transverse optical phonons. The gain is provided by an intersubband transition in a quantum cascade structure. The polaritons at h$\nu$ = 45.4meV (corresponding to an emission frequency of 10.4THz) are formed by the transverse AlAs phonon mode of monolayer thin AlInAs layers coupled to the optical modes of a Fabry-Perot cavity. The frequency location of the laser mode is in good agreement with the computed polaritonic dispersion and allows to quantify the constituent fractions of the emitted polaritons that reach a maximum of 50% for the phonon fraction. A fraction of the gain (between 2-5%) originates directly from the coupling between the intersubband and the phonon polarizations. The device exhibits a very low temperature dependence of its threshold current, as well as the capability to operate in very thin ($\lambda/20$) optical cavities.