Speaker
Description
The ET-HF (high-frequency interferometer) is expected to operate at very high circulating optical powers of around 3 MW to enhance sensitivity at high frequencies; however, such extreme power levels inevitably introduce parametric instability (PI) as a critical challenge for stable operation. Parametric instability arises from the three-mode interaction between the fundamental optical mode, higher-order optical modes, and the acoustic eigenmodes of the test masses, where radiation pressure transfers energy into mechanical vibrations, leading to exponential growth and potential loss of interferometer lock. Understanding and mitigating PI is therefore essential for reliable high-power operation.
ET-OPT (see A. Goodwin-Jones' talk) is a proposed 10 m-scale prototype cavity at UCLouvain, Belgium, designed to achieve a power density comparable to ET-HF while intentionally operating in a regime where PI is observable. It serves as an experimental testbed to study PI under controlled conditions and to develop and validate mitigation strategies. Other research missions (see R. Cabrita's poster) carried out at ET-OPT include thermally correlated effects such as thermal transients and their control, as well as the mitigation of coating thermal noise.
This work presents the engineering design choices of ET-OPT that enhance the observability of PI, and systematically investigates how these parameters influence its behavior. The preliminary research provides an experimental pathway to test mitigation schemes and delivers concrete insights for the design, operation, and risk assessment of PI in ET-HF.