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PLEASE NOTE: If a candidate gives a layman's talk, the livestream will start fifteen minutes earlier.

The ability to control and manipulate light with light is crucial for optical information and communication technology. However, all-optical information processing is hindered by the absence of interactions between photons in linear materials. Nonlinear materials mediate effective photon-photon interactions but require large light intensity.

Optical resonators store and confine light for many optical cycles, which increases the interaction time and reduces the nonlinearity threshold. However, monolithic optical resonators have limited variability of the intra-cavity medium. Instead, a wide variety of materials can be easily integrated in tuneable open access microcavities, making them an ideal platform for exploring novel materials for nonlinear optics.

In this thesis, we present experiments using coherently driven tuneable open access microcavities, hosting either oil or a perovskite semiconductor. In chapter 2, we demonstrate steady-state room-temperature superfluidity of photons in an oil-filled cavity and reveal how the fluid dynamics are influenced by the nonlocality of the effective interactions mediated by the oil.

Chapters 3 and 4 describe experiments using a halide perovskite semiconductor in an open-access microcavity in a closed-cycle cryostat. We demonstrate continuous-wave nonlinearity in the halide perovskite material through optical biostability and reveal signatures of a phase transition in the temperature dependence of the nonlinearity strength. Next, we investigate the emergence of irreversibility in the bistable switching of our perovskite cavity.

Finally, we present in chapter 5 experimental observations of fast nonlinearity-enabled oscillations in the light intensity, that occur despite the slowness of thermal nonlinearity of the oil.