We study mode competition in a multimode phonon laser comprised of a Fabry-Perot cavity employing a highly reflective membrane as the output coupler. Mechanical gain is provided by driving the cavity with a blue-detuned pump laser, and many mechanical modes are coupled to the intracavity radiation pressure. We calculate the gain for arbitrary oscillation amplitude, and find, just as in a homogeneously broadened conventional laser, that strong oscillation in one mode suppresses the gain in other modes. For sufficiently strong oscillation, we calculate that the gain of the other modes actually switches sign and becomes damping, a process we call anomalous cooling. We demonstrate mode competition in the time domain and find excellent agreement with the predictions of our theory, including anomalous cooling.
Physical Review Letters
Opto-mechanics, Coupled oscillators, Laser Oscillations