Sound amplification by stimulated emission of radiation field. For typical conditions of the optical micro-resonators, the photonic molecule behaves as a two-level laser system. Nevertheless, there is a bizarre inversion between the roles of the active medium and the cavity modes (laser field). The medium becomes purely optical and the laser field is provided by the material as a phonon mode. An inversion produces gain, causing phonon laser action above a pump power threshold of around 7 μW. The proposed device is characterized from a continuously tunable gain spectrum that selectively amplifies mechanical modes from radio frequency to microwave rates. Viewed as Brillouin process, the system accesses
Sound amplification by stimulated emission of radiation means that, since bosons with the same energy can occupy the same place in space, phonons and photons are force carrier particles and they have integer spins. There are more allowed states available for occupancy in a phonon field than in a photon field. Therefore, since the density of terminal states in the phonon field exceeds that in a photon field (by up to ~10), phonon emission is by far the more likely event. We could also imagine a concept where the excitation of an electron briefly leads to vibration of the lattice and thus to phonon generation. The vibration