Novel Chromatic Confocal Differential Interference Contrast Prototype

By combining classic differential interference contrast (DIC) with the chromatic confocal principle, we show that phase-shifting calibration can be avoided in DIC by using spectral information induced by the investigated sample. The created spectral fringe can be further used to unwrap the phase. This unwrapping is limited by the spectral resolution of the spectrometer. Therefore, the depth-difference around a single measurement point can be determined instantaneously. To reconstruct the depth profile, the integration of a depth-gradient is necessary. By combining the depth information of the chromatic confocal carrier signal with the differential depth information of the carried DIC signal, the accumulation of measurement uncertainty can be reduced. To our best knowledge, the proposed chromatic confocal differential interference contrast (CCDIC) is a novel profile reconstruction principle. To verify the feasibility of the CCDIC, a prototype probe with an adjustable shear and phase has been developed. Preliminary experiments achieve sub-micrometer depth resolution. A current challenge requiring further work is the stable unwrapping of the phase-difference by spectral frequencies.