Implementation of accurate phase shift in Fizeau interferometer

To realize the high accuracy measurement of optical surfaces by a phase-shifting Fizeau interferometer,a synchronous acquisition phase-shifting system in the interferometer was established,and an accurate phase shifting method was researched.First,the composition and working principle of the phase-shifting system were introduced.Then,the velocity of PZT phase shifter during measurement was calculated.Since there exist defocus errors as well as speed-up and speed-down steps during phase shift,the moving process of phase shifter was detailedly designed.Finally,the phase shifter was calibrated.A verified experiment was carried out on the modified interferometer,and it shows that the RMS simple repeatability is λ/11 340.Comparative measurement was also carried out with two same components between the modified interferometer and the Verifire XP/D interferometer(Zygo company),and the RMS difference is about 0.9 nm.It can be seen that the repeatability and accuracy of this phase-shifting system and phase-shifting method have satisfied the requirement of nano-scale form measurement,which can provide references for developing high accuracy phase-shifting interferometers.