The phase-shifting algorithms are essential for a Fizeau interferometer to reconstruct the topography of the optical element’s surface or wavefront. There are differences between different algorithms for reconstruction results, especially for the suppression of noise. To acquire a more accurate Instrument transfer function (ITF) which reflects the axial spatial frequency response of a Fizeau interferometer, the algorithm transfer function which represents the characteristics of the calculation process in spatial frequency was proposed. In this paper, numerical simulations calculated and analyzed several transfer functions of the well-known phase-shifting algorithms. Then, the ITFs of a step plate with a height of 118 nm were measured with different algorithms by experiments and the results were analyzed. The simulations and experimental results indicate that the phase-shifting algorithm has an effect on the ITF measurement but it is not a key factor affecting the ITF measurement.
Optical flats used to realize pulse compression grating in ultra-intense and ultra-fast laser systems are large and have stringent face form requirements. This study employed an interferometer with an optical aperture of Φ800 mm to meet the demand for high-precision surface form measurements of meter-scale optical flats. The measurement accuracy of this interferometer improved using absolute surface form measurement. In addition, the full-aperture reflection surface form measurement of meter-scale optical flats was realized by exploiting sub-aperture stitching technology. The absolute measurement principle, based on the combination of rotational averaging and parity function, was used to calibrate the system error of the interferometer for absolute surface form measurement. The absolute surface form peak-to-valley (PV) repeatability (2σ) of the calibrated interferometer system error was 1.96 nm, and the root mean square (RMS) repeatability (2σ) was 0.44 nm. The calibration results show that the absolute surface-form measurement technique can effectively remove the interferometer system error and improve the surface-form measurement accuracy of the optical flat. The calibrated interferometer was then used to perform a two-dimensional stitching inspection of the meter-scale optical flat. The repeatability (2σ) of the PV value was 21.52 nm, whereas the repeatability (2σ) of the RMS value was 4.43 nm for a 1,680 × 1,100 × 200 mm flat. The measurement results show that the high-precision surface form measurement of meter-scale optical flats was realized.
Optical flats used to realize pulse compression grating in ultra-intense and ultra-fast laser systems are large and have stringent face form requirements. This study employed an interferometer with an optical aperture of Φ800 mm to meet the demand for high-precision surface form measurements of meter-scale optical flats. The measurement accuracy of this interferometer improved using absolute surface form measurement. In addition, the full-aperture reflection surface form measurement of meter-scale optical flats was realized by exploiting sub-aperture stitching technology. The absolute measurement principle, based on the combination of rotational averaging and parity function, was used to calibrate the system error of the interferometer for absolute surface form measurement. The absolute surface form peak-to-valley (PV) repeatability (2σ) of the calibrated interferometer system error was 1.96 nm, and the root mean square (RMS) repeatability (2σ) was 0.44 nm. The calibration results show that the absolute surface-form measurement technique can effectively remove the interferometer system error and improve the surface-form measurement accuracy of the optical flat. The calibrated interferometer was then used to perform a two-dimensional stitching inspection of the meter-scale optical flat. The repeatability (2σ) of the PV value was 21.52 nm, whereas the repeatability (2σ) of the RMS value was 4.43 nm for a 1,680 × 1,100 × 200 mm flat. The measurement results show that the high-precision surface form measurement of meterscale optical flats was realized.
In this paper, we present a wide-spectrum plug-and-play Fizeau interferometric system, which can complete precision interferometric measurement at any wavelength in the range of 600-1600 nm with a maximum measurement aperture of 150 mm. The system can be designed with multiple optical fiber input terminals, different wavelengths share only one set of interferometric system, and no components need to be adjusted when switching the working wavelength. The development of the system is helpful to accurately measure the surface profile error of coated optical elements at a specified wavelength.
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