| Summary: | A method is proposed to expand the Z-directional measurement range of a fiber-based dual-detector chromatic confocal probe with a mode-locked femtosecond laser source. In the dual-detector chromatic confocal probe, the <i>Z</i>-directional displacement of a measurement target is derived from the peak wavelength in the normalized intensity ratio from the two light intensities obtained by the two identical fiber detectors. In this paper, a new method utilizing the main-lobe and side-lobes of axial responses acquired from both the normalized intensity ratio <i>I</i><sub>a</sub> and the invert normalized intensity ratio <i>I</i><sub>n</sub>, which is the inverse of <i>I</i><sub>a</sub>, is proposed to obtain the seamless relationship between the peak wavelength and the <i>Z</i>-directional displacement of a measurement target. Theoretical calculations and experimental investigation are carried out to demonstrate the feasibility of the proposed measurement range expansion method.
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