Wide measurement range scanning heterodyne interferometer utilizing astigmatic position sensing scheme

A scanning heterodyne I/Q-interferometer scheme is proposed to overcome phase ambiguity caused by the periodic nature of its phase-dependent signal. A position sensing scheme using an astigmatic method in the confocal arrangement has been interfaced to the interferometer to retrieve the real phase value during a scanning process. The experimental results show that the vertical measurement range can be expanded up to 16 μm. The potential of this interferometer on the scanning microscopy of a rough surface is discussed.