Abstract

Accurate measurement of large step heights using multiple-wavelength holographic interferometry is realized using laser diodes. Due to the high-resolution wavelength tunability of such lasers, a pair of holograms with a wavelength difference of less than $0.01\mathrm{nm}$ is recorded and used to extract a phase difference having a large synthetic wavelength. Phase differences with synthetic wavelengths ranging from $2.5\text{to}73\mathrm{mm}$ are extracted by using pairs of holograms with wavelength differences between 0.3 and $0.01\mathrm{nm}$. By combining the phase differences, measurements with a step height of $18\mathrm{mm}$ and an rms error of $0.04\mathrm{mm}$ could be achieved. The requirements for performing the phase unwrapping are discussed. Precise knowledge of the recording wavelengths is required to correctly perform this unwrapping.

© 2008 Optical Society of America

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