Cavity-Enhanced Detection System with an Optically-Feedbacked Diode Laser for Faraday Effect Measurements

We present a cavity-enhanced spectroscopic detection system in which a single cavity serves two functions: signal enhancement and locking of a laser frequency. A GaAlAs diode laser was frequency-locked by optical feedback to the resonance of an external Fabry-Perot optical cavity into which a solenoid filled with air was placed. By measuring the Faraday rotation due to air subjected to a longitudinal magnetic field, we showed that the ratio of the effective optical path length to the single-pass length was 32.