We propose a new interferometer system, the cascade Twyman interferometer (CTI), that can actively compensate for systematic errors. It adds an extra channel to the Twyman interferometer and uses polarized beam interference to separate the three beams. Subsequently, three interferograms, or two-by-two interferences of the three beams, can be obtained. Finally, the absolute surface distribution of the test mirror is calculated using the three-flat mutual inspection. The simulation showed that the CTI was only affected by the wavefront transmission error, which was negligible. In the experiment, the RMS repeatability of CTI was <10-4 lambda. Meanwhile, compared with the even and odd function methods, the results were similar, with a difference between the Zernike coefficients of <0.0028 lambda. This indicates that CTI is an efficient and accurate interferometer.
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