Spectral interferometer using sinusoidal phase modulation and back-propagation method

The multi-wavelength back-propagation (MWB) method has been developed for measuring positions of multiple reflecting surfaces longer than the optical wavelength. In this study, we demonstrate one dimensional profile measurement of a glass film by a sinusoidal phase modulating (SPM) spectral interferometer with MWB method. Displacements of front and rare surfaces of the glass film vibrating with 9.7 Hz are exactly measured. The measurement repeatability obtained from 9 repeatedly-measured results is 4.7 nm in a standard deviation.