Measurement and calibration of interferometric imaging aberrations

Phase-shifting interferometry is the standard method for testing figure err or on optical surfaces. Instruments measuring spheres and flats are readily available, but the accurate measurement of aspheres requires null correcti on. One problem with the general (nonull) testing of aspheres is the loss o f common path. Systematic errors are introduced into the measurement by the fringe imaging optics. The sources and types of error are reviewed, as wel l as their effect on a wave-front measurement. These nonnull errors are pre dicted generally, with third-order analytic expressions derived for a tilte d or a defocused test surface. An interferometer is built to test the expre ssions. The imaging system is a single lens, nominally image telecentric. M easurements are performed on a test surface defocused from -5 to 5 mm. The resulting measurement bias is shown to be in goad agreement with third-orde r aberration theory predictions. (C) 2000 Optical Society of America.