Traceable methods for vertical scale characterization of dynamic stroboscopic scanning white-light interferometer measurements

Stroboscopic scanning white-light interferometry (SSWLI) can be used for 3D imaging of oscillating samples. It allows measurement of micrometer to millimeter size samples with nanometer vertical precision. Unlike coherent light source systems the SSWLI can measure unambiguously samples with vertical steps. Traceability of the vertical displacement measurement is important with SSWLI since the height measurement is not related to any specific monochromatic light wavelength. For static measurements SSWLI can be calibrated using, e.g., step height standards, but to characterize dynamic measurements traceable samples with accurate motion are needed due to error sources related to the frequency response of the SSWLI. In the presented method, SSWLI measurements are performed on dynamic transfer standards, which are characterized using a laser interferometer traceable to the SI meter. In this work dynamic SSWLI measurements at subkilohertz to 10.7 kHz frequencies with micrometer range displacement are characterized. The expanded uncertainty (k=2) was 9.6 nm for a measured displacement of 766 nm at 10.7 kHz. The methodology can be used up to the frequency limits of the SSWLI using suitable samples.