Aspheric lens testing by means of compact radial shearing interferometer with two zone plates

Aspheric surface testing technique with radial shearing interferometer has been developed.The principle of the measurement is based on the radial shearing interference in which the measuring wavefront from the entire mirror surface under test is referred to that of the central part.The compact and low-cost radial shearing interferometer is constructed with two Fresnel zone plates,which are designed and fabricated by photographic processing.Radial shearing interferogram is detected by a CCD camera and processed by a computer.Fringe phase of shearing interferogram is evaluated by fast Fourier transform(FFT) algorithm and testing wavefront is reconstructed.The measurement for standard lens show the accuracy to be around λ/5 P-V and λ/10 RMS.The experiments show that this stable interferometer can be applicable to the in-process measurement for aspheric lens.