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An in-situ method for measuring the non-linear response of a Fabry-Perot cavity

High finesse Fabry-Perot(FP) cavity is a very important frequency reference for laser stabiliza- tion, and is widely used for applications such as precision measurement, laser cooling of ions or molecules. But the non-linear response of the piezoelectric ceramic transducer (PZT) in the FP cav- ity limits the performance of the laser stabilization. Measuring and controlling such non-linearity are important. Here we report an in-situ, optical method to characterize this non-linearity by measuring the resonance signals of a dual-frequency laser. The differential measurement makes it insensitive to laser and cavity drifting, and has a very high sensitivity. It can be applied for various applications with PZT, especially in an optical lab.