Phase measurements with wide-aperture interferometers

An interferogram produced by wide-aperture interferometers is studied both theoretically and experimentally. The fringe spacing is shown to increase n onlinearly with the numerical aperture and the fringe envelope to become na rrower as the numerical aperture is increased. Phase measurements with wide -aperture interferometers therefore require calibration, and the phase can be measured only over a limited range. A calibration is given for accurate phase measurements, and the range over which the phase can be measured is c alculated. Experimental measurements are presented and compared with theory . (C) 2000 Optical Society of America. OCIS codes: 120.5050. 120.2830, 120. 3180, 180.3170.