Polarization interferometer for measuring small displacement

A homodyne polarization laser interferometer is presented for high speed measurement of small displacements. No modulation technique is used, so the opto-mechanical set-up is relatively simple. The dual beam arrangement enables the displacement to be measured whilst the use of polarization interferometry enables the determination of the directional nature of the displacement. Another feature of this interferometer lies in the fact that it is also suitable for the measurement of head-media spacing of a hard disk drive. Combined with the electronics used at present, sub-nanometre resolution is achievable. Its measurement bandwidth is limited only by the sampling rate of the A/D board being used.