Low-Noise Crystalline Mirrors for Precision Metrology

The ultimate performance of high-precision optical interferometers depends crucially on the mechanical damping in the constituent materials of the cavity end mirrors. Such systems are applicable to a variety of fields, including gravitational wave detection, laser stabilization for optical clocks, quantum optomechanics, as well as precision tests of modern physics. Unfortunately, existing high-quality optical coatings based on Ta2O5/SiO2 suffer from excessive loss, thus limiting the noise performance of these advanced optical systems. Recent investigations into monocrystalline Bragg mirrors based on AlGaAs heterostructures have revealed that this materials system is an extremely promising low phase-noise alternative to existing state-of-the-art dielectric mirrors for use in high- performance interferometry. We will investigate the ultimate limits with respect to both the optical and mechanical losses in this materials system and we propose a novel bonding-based transfer process for the construction of crystalline AlGaAs mirrors on bulk sapphire substratesthis includes the possibility to realize curved mirrors. By overcoming the impediment of high mechanical damping as found in Ta2O5/SiO2 multilayers, we expect to demonstrate optical cavities with record low thermal noise performance and ultimately to make low phase-noise crystalline mirrors available to the scientific community.

The ultimate performance of high-precision optical interferometers and optical reference cavities depends crucially on the mechanical damping in the constituent materials of the cavity end mirrors. Such systems are applicable to a variety of fields, including gravitational wave detection, laser stabilization for optical clocks, quantum optomechanics, as well as precision tests of modern physics. Unfortunately, existing high-quality optical coatings based on Ta2O5/SiO2 suffer from excessive mechanical loss, thus limiting the noise performance of these advanced optical systems. Recent investigations into monocrystalline Bragg mirrors based on AlGaAs heterostructures have revealed that this materials system is an extremely promising low phase-noise alternative to existing state-of-the-art dielectric mirrors for use in high-performance applications. We have investigated the limits with respect to both the optical and mechanical losses in this material system. Using a bonding-based transfer process, which has also been studied, crystalline AlGaAs mirrors on bulk sapphire substrates can be created including the possibility to realize curved mirrors. We have demonstrated optical cavities with the expected record low thermal noise performance, hence overcoming the impediment of high mechanical damping as found in Ta2O5/SiO2 multilayers. Some of the developments have by now been commercialized.