A recently introduced wavefront analyzer, based on a Fresnel-lens arra
y, is improved by incorporating phase-shifting procedures. The resulti
ng compact and stable interferometer can measure wavefront distortions
with extremely high accuracy. In our experiments, with no special eff
orts at environmental isolation, the instrumental noise level was unde
r 0.02 lambda. (C) 1997 Society of Photo-Optical Instrumentation Engin
eers.