Phonon Laser Action in a Tunable Two-Level System

TLDR

The phonon analog of an optical laser has long attracted interest, and viewed as a Brillouin process the system accesses a regime where the phonon plays the role traditionally assigned to the Stokes wave. The study demonstrates a compound microcavity system coupled to a radio‑frequency mechanical mode that functions as a two‑level laser analog. The microcavity is coupled to the mechanical mode to achieve phonon laser action. Inversion yields phonon laser action above a ~7 µW pump threshold, with a continuously tunable gain spectrum enabling selective amplification from radio‑frequency to microwave rates, potential switching between phonon and photon laser regimes, and mechanical mode cooling.

Abstract

The phonon analog of an optical laser has long been a subject of interest. We demonstrate a compound microcavity system, coupled to a radio-frequency mechanical mode, that operates in close analogy to a two-level laser system. An inversion produces gain, causing phonon laser action above a pump power threshold of around 7 microW. The device features a continuously tunable gain spectrum to selectively amplify mechanical modes from radio frequency to microwave rates. Viewed as a Brillouin process, the system accesses a regime in which the phonon plays what has traditionally been the role of the Stokes wave. For this reason, it should also be possible to controllably switch between phonon and photon laser regimes. Cooling of the mechanical mode is also possible.