Phase retrieval from carrier frequency interferograms: reduction of the impact of space-variant disturbances

Abstract

Phase “extraction” by using temporal phase shifting is sensitive to vibrations and drifts, producing systematic phase errors periodic withtwice the fringe frequency. This error source may be avoided by evaluating only single carrier frequency interferograms, which makesthe procedure immune against vibrations and drifts provided that the integration time is short enough to freeze the fringe pattern.However, the phases extracted from single interferograms in this way often show local irregularities depending on the mean phase of theinterference pattern. Such local phase irregularities are caused by local disturbances in the light path like specks and dust particles onthe optical components of the interferometer. Moreover, since digitized data are gathered, there is a nonlinear processing step involvedwhich is also responsible for the generation of such irregularities. Here, it is proposed to use a set of suitably combined phase-rampedinterferograms to reduce phase dependent irregularities. The proposed averaging technique also reduces edge ringing effects known fromFourier evaluation procedures. Since the imaging optics also contributes to the phase to be measured when tilted wavefronts are used,calibration is mandatory. The calibrated state is only valid if strict rules considering fringe number per diameter as well as the position of the wedge in the interferometer are maintained in the measuring process.

Keywords

• interferometry
• phase retrieval
• carrier frequency
• synchronous detection