Active suppression of air refractive index fluctuation using a Fabry–Perot cavity and a piezoelectric volume actuator

Air refractive index fluctuation ($\mathrm{\Delta }{n}_{\text{air}}$) is one of the largest uncertainty sources in precision interferometry systems that require a resolution of nanometer order or less. We introduce a method for the active suppression of $\mathrm{\Delta }{n}_{\text{air}}$ inside a normal air-environment chamber using a Fabry–Perot cavity and a piezoelectric volume actuator. The temporal air refractive index ($n_{\text{air}}$) at a local point is maintained constant with an expanded uncertainty of $\sim 4.2\times {10}^{-9}$ ($k=2$), a sufficiently low uncertainty for precise measurements unaffected by $\mathrm{\Delta }{n}_{\text{air}}$ to be made inside a chamber.