A line-scanning chromatic confocal sensor for three-dimensional profile measurement on highly reflective materials

We developed a practical Line-Scanning Chromatic Confocal Sensor (LSCCS) that can generate three-dimensional (3D) points with up to 32 000/s with a high-precision motion device. An optical route of line-scanning confocal spectroscopy is designed and verified by simulation. The LSCCS is composed of a white laser source, a chromatic confocal optics, and a self-developed spectrometer. The chromatic confocal optics consists of a slit, a chromatic lens (dispersive objective lens), and a beam splitter, and the spectrometer consists of an adjustable slit, a collimating lens, a blazed grating, a focusing lens, a CMOS, and an image processing circuit. The slit and the chromatic lens are designed for a line focus, and the polarizing beam splitter is selected to maximize the white light power collected by the CMOS. The motion device is made to realize the full-field 3D scanning. The key algorithms involved are developed to accurately restore the peak wavelength that includes the position information of the measured surface from the collected spectral image. Theoretical analysis and simulation showed that the corresponding resolutions in Z (depth), X (direction of optical fibers layout), and Y (direction of line-scanning) directions are 0.6, 10, and 5 µm, with a line length of 8 mm and a depth field of 2.4 mm. Experimental results showed that the sensor produces a measurement accuracy of 0.886 µm and a scanning speed of 90 fps. It is of great significance for the accurate measurement of the 3D profile and thickness on the highly reflective materials in the fields of optics, semiconductors, or micromechanics.