Frequency to Voltage Converter as a Phase Controller in Phase Shifting Interference Microscopy

A new system for the control of a piezoelectric device is introduced. It works as a phase shifter in an interference optical microscope. This circuit translates controllable constant frequency signals, generated with a standard sound card, to electrical signals with constant voltage through a frequency-to-voltage converter; this full analog conversion allows for producing voltage steps of 16 mu v, which is a better resolution than a commercial digital to analog converter working (in the desired voltage range), and hence, results in an arbitrary phase uncertainty under 3%. The calibration method allows for verification of the displacement's steadfastness in the arbitrary phase, and for diagnosing of errors that could alter the experimental interferograms. To check the system calibration, it was experimentally and successfully tested on a silicon surface with rectangular holes of known depth.