Abstract
Mio developed the LASER frequency stabilization by using an optical cavity comprising birefringent mirrors, the defect is that birefringence of the cavity is inherent and unmodifiable. In our experiment, stress is exerted upon the cavity to modify birefringence of the cavity and we could upgrade the effect of LASER frequency stabilization by moderate stress. Hansch used the cavity that a polarizer placed inside to lock the frequency of a laser, but the polarizer degrade finesse of the cavity because of absorption and scattering. To avoid this trouble, the cavity that a polarizer placed inside is replaced by a birefringent cavity.