A locking scheme for optimizing the length of an optical cavity contai
ning a birefringent crystal is presented. This scheme is a variation o
n the well known polarization sensitive locking scheme. The birefringe
nce of the crystal introduces a polarization dependent phase differenc
e which can be used to generate a locking signal. The principles of th
e locking system are described and verified experimentally. (C) 1997 E
lsevier Science B.V.