Extended-focus phase imaging with an interferometric confocal microscope

We describe results obtained when a modified differential interferometer is used in a new imaging modality that we call extended-focus phase imaging. This modality is the phase analog of extended-focus imaging used in the confocal microscope. Our technique is applied to the measurement of the differential phase response of minute topographical variations on tilted samples. Results are presented that demonstrate the ability of the technique to produce high lateral resolution phase scans on samples with long-range warp and tilt over a range much greater than the depth of field of the objective lens, thus effectively allowing the depth of field of the phase microscope to be increased indefinitely.