Optimisation of a four-mirror cavity for a titanium laser

A theoretical analysis is reported of four-mirror Z-shaped (folded) cavities used in single-mode titanium lasers. A study is made of the sensitivity of the waist radius of a laser mode in such cavities to longitudinal displacements of the mirrors and to fluctuations of the optical power of a thermal lens induced in the active element of the laser. A method is proposed for the design of a cavity with the minimum sensitivity to these perturbations.