New publication
M. Vretenar, M. Puplauskis and J. Klaers, “Mirror Surface Nanostructuring via laser direct writing – characterization and physical origins”, Advanced Optical Materials 11, 2202820 (2023). link
How can you control the motion of light in resonators? This is a challenge that our research group has been working on intensively for several years. Light in a resonator propagates essentially parallel to the optical axis, but can also make a small angle to it, resulting in motion in the plane of the resonator. In recent years we have developed various methods of better controlling this in-plane movement. For example, we have introduced a thermo-responsive polymer into the resonator, with which this movement can be influenced by changing the refractive index [Dung et al., Nature Photonics 11, 565 (2017)]. Complementary to this, we have also been researching how to nanostructure the surface of the mirrors, as this effectively creates a potential energy landscape for the photons that equally controls their motion.
It turns out that a highly precise nanostructuring of mirror surfaces is surprisingly easy to achieve by incorporating an absorptive layer in the dielectric stack of a mirror. By locally heating this layer with a focused laser beam it is possible to create long-term stable surface profiles with highest precision. A first publication on this method was released in 2020 [Kurtscheid et al., EPL 130, 54001 (2022)]. In the past two years, we have successively improved the technical implementation of this method and worked on a deeper understanding of the physical processes behind the nanostructuring process. The advantages of this novel type of nanostructuring of mirror surfaces can be summarized as follows: routinely achievable Angstrom-level precision, preserves highest mirror reflectivities, surface structures are long-term stable, cost-effective and fast. These properties make this technique particularly suitable for many applications in high-finesse resonators, e.g., cavity ringdown spectroscopy or interferometric precision measurements like gravitational wave detection. Wavefront shaping (particularly in the UV) also seems to be a natural application.
You might also be interested in visiting our friends at Midel Photonics.