Observation of strong light-matter coupling by spectroscopic ellipsometry

We report on the observation of strong coupling between excitons and cavity photons in a ZnO-based microresonator up to room temperature. The ZnO-based resonator was grown by means of pulsed laser deposition (PLD) on c-sapphire substrate and consists of a half-wavelength ZnO-cavity between two Bragg reflectors, each made of 10.5 layer pairs of yttria stabilized zirconia and Al2O3. Angle-resolved spectroscopic ellipsometry revealed the resonator to be in the strong coupling regime at room temperature. This was confirmed for temperatures between 10 K and 290 K by means of angle-resolved photoluminescence and reflection experiments. Prior studies on a Fabry–Perot resonator containing a half-wavelength YSZ-cavity (empty resonator) demonstrate the ability of ellipsometry to gain comprehensive information on mode-structure properties of resonators without coupling effects.