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 start to bunch according to phase and they become coherent. Thus, the electromagnetic field is amplified. We note that, in the case of the piezoelectric radiators usually used to generate ultrasound, only the working surface radiates and therefore the working system is two-dimensional. On the other hand, a sound amplification by stimulated emission of radiation device is a three-dimensional system, since the entire volume of the active medium radiates. The active medium gas-liquid mixture fills the resonator. The bubble density in the liquid is initially distributed uniformly in space. Since the wave propagates in such a medium, the pump wave