LATERAL-SHEARING INTERFEROMETER USING SQUARE PRISMS FOR OPTICAL-TESTING OF ASPHERIC LENSES

We present a lateral-shearing interferometer specially devised for pro duction-line inspection of aspheric lenses. The interferometer constit utes four right-angle prisms, whose relative sliding motions provide t he lateral shearing and phase shifts necessary for measuring the beam wavefront collimated by the lens under test. The prisms are held toget her face to face using index-matching oil, so environmental disturbanc es from external vibration and atmospheric turbulence can be minimized . Furthermore, a special phase-measuring algorithm of least-squares ty pe is adopted to compensate for the phase shift error caused by the va riation in thickness of the index-matching oil holding the prisms. Exp erimental results prove that the interferometer provides a measuring r eproducibility of the order of one hundredth of the light's wavelength .