Polarized optical heterodyne profilometer

A quasi common path polarized optical heterodyne interferometer with an aluminum coated polarized beam splitter is proposed in order to sense the surface profile. The heterodyned P wave is generated by two acousto-optic modulated P waves with different frequencies in the Mach-Zehnder interferometer. So is the heterodyned S wave. Both heterodyned P wave and S wave propagate through quasi common optical path in the interferometer. An aluminum coated polarized beam splitter was used to conduct a quasi common path configuration to sense the surface profile. The stability of the interferometer was ±0.25°/0.5 h and 0.5% in phase and amplitude respectively. The height sensitivity was 2 Å and the lateral resolution was 2 μm in the experiment. In case of a birefringence lens or a Wollaston prism is suggested to replace the aluminum coated polarized beam splitter, a novel polarized common path profilometer with better stability is expected.