Two-membrane cavity optomechanics*

The optomechanical behaviour of a driven high finesse Fabry–Pérot cavity containing two vibrating dielectric Si3N4 membranes is presented. The first experimental characterization of the optical, mechanical, and especially optomechanical properties of a sandwich constituted of two parallel membranes within an optical cavity will be presented. We find that the optomechanical coupling strength is enhanced by constructive interference when the two membranes are positioned to form an inner cavity which is resonant with the driving field. Furthermore, the behaviour of the non-linear dynamics of such a system in a pre-synchronization regime will be discussed. In this regime we find that both large and small amplitude resonator motions are transduced in a nontrivial way by the non-linear response of the optical probe beam. Moreover the slope with which the temporal dynamics of the mechanical oscillator reaches a limit cycle, allows us to determine, in a simple and consistent way, the single–photon optomechanical rate, without the need of knowing the bath temperature, providing a novel procedure for the full characterization of an optomechanical system.