Abstract

Tunable single longitudinal mode (SLM) operation is essential for many spectroscopic applications. Often, however, reaching the required spectral purity in dispersive cavity geometries can compromise the output power of the laser and cause high oscillation thresholds. We report on a grazing incidence cavity which has been integrated with a linear cavity to form a Michelson interferometer with the inclusion of an inexpensive optic. Dramatic improvements in output efficiency and threshold are observed in this cavity over the conventional grazing incidence design^1,2. The additional optic, in this case, is a glass slide known as the zero-order mirror (figure 1). The interferometric nature of the cavity places an additional constraint on the allowed resonant modes, since each cavity must be simultaneously satisfied, resulting in an increase in the cavity mode spacing. This allows a single mode to be readily isolated. By modelling the cavity geometry, we can predict the mode behaviour accurately and position the optical components to maximise the mode spacing. In order to demonstrate this, we have designed a pulsed Ti:sapphire laser pumped at 532 nm, although in practise other gain media could be used. Using our software-driven piezoelectric transducer (PZT) on the zero-order mirror, we are able to lock the cavity to a single mode with a bandwidth of 200 MHz, limited by the resolution of the 10 GHz etalon used, whilst maintaining a tuning range of > 100 nm.

© 1996 IEEE