Fig. 1. Measuring principle of double-hole point diffraction interferometer

Fig. 2. Schematic diagram of system errors calibration. (a) Point diffraction measurement mode;(b) system errors measurement mode

Fig. 3. Interference diagrams in DHPDI experiment. (a) System error interferogram; (b) point diffraction interferogram

Fig. 4. Wavefront aberration detection results of the measured objective lens and the 5--37 Zernike polynomials fitting. (a) System error measurement results, 75.66 nm RMS; (b) point diffraction measurement results, 76.92 nm RMS; (c) wave aberration detection results, 8.45 nm RMS

Fig. 5. Interference diagrams in DFPDI experiment. (a) System error measurement results; (b) point diffraction measurement results

Fig. 6. Wavefront aberration detection results of the measured objective lens and the 5--37 Zernike polynomials fitting. (a) System error measurement results, 75.69 nm RMS; (b) point diffraction measurement results, 77.26 nm RMS; (c) wave aberration detection results, 8.52 nm RMS

Fig. 7. Intensity distribution and contrast curve of interferograms of the DHPDI and DFPDI in X direction under two measurement modes. (a) Intensity distribution of two kind of interferograms under the mode of system error measurement; (b) contrast curve of two kind of interferograms under the mode of system error measurement; (c) intensity distribution of two kind of interferograms under the mode of point diffraction measurement; (d) contrast curve of two kind of interferograms under the mode of point diffraction measurement