Dispersion lens for chromatic confocal spectral interferometry

The dispersion element that can generate axial dispersion is an essential component of chromatic confocal spectral interferometry (CCSI). In this study, we presented a CCSI system that uses refractive dispersion lens instead of the commonly used diffractive optical element (DOE) to promote imaging quality with a large axial measurement range. The parameters of the dispersion lens are analyzed based on CCSI. Moreover, the design of a dispersion lens with an axial dispersion close to 1 μm in the wavelength range of 430-710 nm is also presented. The experimental results indicate that even under non-ideal conditions like suboptimal light spectrum, the axial dispersion larger than 150 µm can still be measured in a 50 nm spectral band. Imaging of the resolution test target demonstrates that the system using dispersion lens achieves a resolution close to 2.76 µm over a range of 150 µm, as opposed to an achromatic lens where the resolution decreases rapidly with increasing defocusing distance. The CCSI system was applied to displacement measurement achieving an axial resolution of 0.2 µm and the measurement errors of less than 0.1 µm.