Metasurface Dichroic Mirrors: Application to Low Quantum Defect Lasers

Over the last decade, lasers with low quantum defects have attracted special attention as they can provide generation of ultra-short pulses simultaneously with high average power. The quantum defect is due to the difference between the energy of the pump and emitting photons. To minimise the thermal load in a laser and provide a wide bandwidth of emission often requires laser crystals with ultra-low quantum defect, having a difference between the pump and the emission wavelength of only a few tens of nm. For example, in the frequently used end-pumping of Yb: crystalline media, the dichroic mirror of the resonator has to exhibit a steep spectral change of reflection to pass the pump and simultaneously to reflect the emission wavelength. The overlap between absorption and luminescence bands in these lasers is a challenge for well-established dielectric coating technology, especially at high laser powers. The recently developed concept of optical metasurfaces based on a single layer of dielectric nanostructures can provide high-reflectivity over a broad spectral range [1] - [2]. However, the application of a metasurface as a mirror with pronounced dichroic properties in power-scalable lasers has not been studied so far. Here we demonstrate the design and implementation of metasurface mirror with a steep spectral change of its reflection. The single-mode stable diode pumped Yb-laser operation has been achieved using this dichroic metasurface mirror (DMM) as a pump cavity mirror.