Tuning a bulk-glass optical current sensor by controlling conditions external to its reflecting surfaces

In a bulk-glass triangular Faraday current sensor, the stringent conditions required to provide critical-angle reflection at each reflecting surface are difficult to achieve. High tolerances for both the optical geometry of the sensor and the wavelength of the laser source are required. Here we present a method of essentially tuning the sensor for optimum operation by matching the angle of reflection at each surface to the wavelength of the laser source. This is done by controlling the gaseous environment external to each of the reflecting surfaces. The technique is demonstrated using sulphur hexafluoride (SF6), which has the advantage of a relatively large refractive index.