High-performance mirrors are employed to construct optical resonators in a variety of applications in optics and photonics. The development of low-loss mirrors such as those readily available throughout the near-infrared spectral region is a long-standing goal for optics and photonics researchers. High reflectance coatings play a significant part in the fabrication of low-loss mirrors.
The key performance metrics for any high reflectance coating technology are: low excess optical loss, combined absorption, and scatter loss. These are currently a few of the main limiting factors for applying optical resonators in the mid-infrared spectral region.
Researchers present high-reflectivity substrate-transferred single-crystal GaAs/AlGaAs interference coatings at a center wavelength of 4.54 µm with record-low excess optical loss below ten parts per million. They realized these high-performance mirrors via a novel microfabrication process. This new process enables reduced scatter loss due to the low surface and interfacial roughness. Low background doping in epitaxial growth ensures strongly reduced absorption.