Resonant cavity design for enhanced magneto-optic measurements

This is an ongoing project which involves both the physics of light propagation and magnetism. The idea of the project is to trap photons inside an optical cavity and force these photons to probe magneto-optically responsive samples multiple times – enhancing the non-reciprocal magneto-optic Faraday rotation (FR) imparted to the optical beam. Often, FR in thin film samples is very sensitive to film thickness and its optical properties. In a conventional single-pass arrangement, the usefulness of this technique is limited to films that are thick enough to result in measurable amount of rotation. Such films are typically opaque and therefore are not amenable to transmission techniques like FR. Previously, we measured FR in submicron ITO films on glass substrates [1]. While the FR signal is dominated by the substrate, we can resolve the FR response of the thin films themselves. However, these films, in terms of their thickness, are already a challenge for our set up. An FR-based based multipass sample probing affords reliability to these measurement via an amplification to the FR response. We are optimistic that such an enhancement in the magnetic effects would drastically improve the signal-to-noise ratio of the received optical signal at the detector. This paper focuses on two things; a) the design and performance measurement of an optical cavity for magneto-optic measurements, and b) preliminary characterization of some simple thin film samples. The future goal would be to characterize more challenging samples and measure their response to modulated magnetic fields inside the cavity.