Chain scission induced by two-photon exposure produces a permanent birefringence in polysilane polymer films, which can be used for the formation of birefringent optical elements. Spectroscopy of the effect for poly(di-n-hexylsilane) reveals an unexpected sharp resonance at 580 nm. A comparison of several polysilanes indicates the effect only occurs in polymers with symmetric or near symmetric sidegroups. Models to explain these observations are introduced and discussed. © 1990.