Iterative algorithm for phase shifting interferometry with finite bandwidth illumination

摘要

While phase shifting interferometry (PSI) has clearly established itself as a powerful tool for surface profiling, two main experimental drawbacks still exist, namely phase-shift errors and non-sinusoidal interferometric signals. These problems cause a fringe print-through pattern in measured phase having a frequency typically double the original fringe frequency. The main tool used to compensate for non-linear phase-shift errors is the least-square phase-stepping method, which is capable of accurately determining the phase separation between consecutive frames as well as phase distribution for each frame. Our work here extends the capabilities of this algorithm so as to account for the effects of a wide bandwidth light source and a higher numerical aperture, which make the interference signal deviate from the ideal sinusoidal signal. We present a simple variable change mechanism that overcomes the coupling that occurs between the planar and depth coordinates and allows for a seamless integration with the standard least-square procedure.