Calibration of interferometer instrument transfer function using reconfigurable sinusoidal phase via spatial light modulator

Extreme surface form measurement accuracy requirements, mainly posed by X-ray and extreme ultraviolet mirrors, have recently inspired great interest in the calibration of the instrument transfer function (ITF) of interferometers. However, no normatively defined ITF calibration method exists, partially due to the fact that a large number of structures with different parameters should be fabricated and the fabrication of the structures itself is difficult. A reconfigurable sinusoidal phase (RSP) method utilizing a high-resolution spatial light modulator (SLM) for ITF calibration is proposed. The inherent wavefront distortion can be compensated to single-nanometer PV and sub-nanometer RMS, which avoids fabricating the high-accuracy flat plate. A number of sinusoidal phases with different spatial frequencies and amplitudes can be flexibly generated. The repeatability and fidelity of the RSP ITF calibration results are verified. The results show that the RSP method is a promising ITF calibration method that accords with the ISO definition of ITF, and it makes it possible to investigate the adequate ITF calibration structure design for individual instruments.