Reduced noise sensitivity method and apparatus for converting an interferogram phase map to a surface profile map

摘要

In the process of converting an interferogram phase map to a surface profile, in the absence of tilt, a histogram of occurrences of phase values is created from phase data. Useful data are identified in bins with contents that exceed a threshold value. Where useful data wrap around the end of the histogram, a selected amount of phase shift is added to the phase data to move them all within the ends of the histogram. Where tilt is present, the phase data are differentiated to produce slope data and a histogram of occurrences of slope values is created. A best-fit amount of tilt is determined from the slope histogram by selecting the bin at the average between two points on the histogram curve that are a predetermined percentage of the maximum height of the curve. Thereafter, the best-fit tilt is subtracted from the original phase data to eliminate tilt.