# An Open Microcavity for Diamond-based Photonics

Flågan, Sigurd. An Open Microcavity for Diamond-based Photonics. 2021, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: https://edoc.unibas.ch/87992/

This thesis reports on the realisation of a high-quality tunable Fabry-Perot microcavity embedded with a diamond membrane. However, the diamond alters the cavity performance, rendering the cavity sensitive to surface related losses. Despite operating in a geometry where the standing wave inside the cavity possesses an anti-node at the diamond surface, quality ($\mathcal{Q}$) factors exceeding $100\,000$ were realised. The benefit of this geometry is the strong confinement of the vacuum electric-field to the diamond – the current cavity design allows for the realisation of Purcell factors exceeding 300, thus increasing the fraction of photons emitted into the ZPL from $3\,\%$ to $89\,\%$.
The versatile design of the microcavity was demonstrated further by enhancing the Raman transition from the single crystalline diamond. Compared to free-space measurements under likewise identical conditions, a 59-fold intensity enhancement was demonstrated. This enhancement factor encompasses the Purcell effect and the improved detection efficiency provided by the cavity. The Raman transition couples to all cavity modes, allowing for in situ optimising and benchmarking the cavity performance. Additionally, it facilitates coupling to the external single-mode detection optics. Further enhancement of the Raman intensity can be achieved by establishing a double resonant condition, with both the pump laser and the Raman transition being resonant. Resonant recirculation of the pump laser increases the power density inside the cavity, providing a platform with prospects of realising a Raman laser with sub-mW threshold pump power. Exploiting a small thickness gradient in the diamond enabled continuous tuning of the double resonance condition across a spectral window of $\sim1\,\textrm{THz}$. The tuning range is only limited by the travel range of the piezo – with an adequate travel range, continuous tuning is, at least in principle, possible across the entire reflective stopband.