Demonstration of the parametric instability suppression through optical feedback

This is the authors' abstract. We don't add key points for this paper.

We demonstrate the suppression of parametric instability in an 80-meter-long Fabry-Perot cavity through optical actuation in an electro-optical feedback loop. The suppression of the high-order mode is achieved by injecting a high-order mode with the same frequency and opposite phase. The beat note signal between the fundamental and high-order mode in the transmission of the cavity is filtered, amplified, and applied to an electro-optical modulator to create a sideband at the high-order mode frequency. Misalignment of the injection couples a small part of this sideband to the high-order mode of the cavity. The paper presents a theoretical analysis and an experimental demonstration of parametric instability suppression for an instability that would normally ring up with a parametric gain of approximately 2.5.