APS/José Tito Mendonça; image on homepage and inset: I. Mahboob/NTT Basic Research Laboratories
(Top) Three-level scheme for a conventional optical laser. (Bottom) Three-level scheme of the phonon laser reported by Mahboob et al. . The mechanical laser cavity features three energy levels, where only phonon transitions are allowed. The laser is pumped to the upper level ωH by a piezoelectric transducer, and stimulated amplified phonon decay radiation onto the intermediate level ωM is observed at a frequency ωL=ωH-ωM. Inset: electron micrograph of the electromechanical resonator used by Mahboob et al.