Full-field chromatic confocal surface profilometry employing digital micromirror device correspondence for minimizing lateral cross talks

Abstract

Full-field chromatic confocal surface profilometry employing a digital micromirror device (DMD) for spatial correspondence is proposed to minimize lateral cross-talks between individual detection sensors. Although full-field chromatic confocal profilometry is capable of enhancing measurement efficiency by completely removing time-consuming vertical scanning operation, its vertical measurement resolution and accuracy are still severely affected by the potential sensor lateral cross-talk problem. To overcome this critical bottleneck, a DMD-based chromatic confocal method is developed by employing a specially-designed objective for chromatic light dispersion, and a DMD for lateral pixel correspondence and scanning, thereby reducing the lateral cross-talk influence. Using the chromatic objective, the incident light is dispersed according to a pre-designed detection range of several hundred micrometers, and a full-field reflected light is captured by a three-chip color camera for multi color detection. Using this method, the full width half maximum of the depth response curve can be significantly sharpened, thus improving the vertical measurement resolution and repeatability of the depth detection. From our preliminary experimental evaluation, it is verified that the AE3σ repeatability of the height measurement can be kept within 2% of the overall measurement range.

A Non-Contact Measuring System for In-Situ Surface Characterization Based on Laser Confocal Microscopy

“…Apart from the pinhole scanning technique, some confocal microscopes use the slit scanning method. The slit scanning method has an advantage of increasing the signal intensity and speed, but its vertical resolution is significantly deteriorated by the lateral cross-talk [ 13 ]. Another critical consideration for surface measurement is the lateral resolution.…”

“…However, due to the complex alignment procedures and limitation of the measurement space, most optical profilers come in desktop form, which make them impractical for in-situ measurement. Chromatic confocal sensors [ 12 , 13 ], which are based on the reflected light spectrum, are also applicable for high-accuracy dimensional measurement. Its highest spatial resolution of 5 μm [ 14 ], however, limits its application for surface roughness measurement.…”

Chromatic confocal matrix sensor with actuated pinhole arrays

“…We thus want to address the main differences to spinning disk systems [8][9][10][11][12]39] and programmable array systems [13][14][15][16]40]. Typically, both spinning disk and programmable array systems realize a lateral movement of the pinhole array during the capture of a single camera frame which then contains the high-resolution information from all lateral positions.…”

“…In this case the z-range of the sensor is evaluated sequentially. Second, the full spectrometric detection can be replaced by a parallel evaluation with RGB detectors [12,25,[35][36][37][38][39][40]. The third approach is based on the assumption that the pinholes of the pinhole array are well separated.…”

Calibration of a Chromatic Confocal Microscope for Measuring a Colored Specimen

“…However, height measurement based on vertical scanning on each measurement point is still the efficiency bottleneck for most conventional, monochrome confocal systems. To perform faster height measurements, the chromatic confocal microscopy (CCM) technique was proposed and has evolved [8]- [10] in recent years. Instead of physical scanning in the vertical direction, a CCM system takes use of a polychromatic light source to emit lights with different wavelengths, which are dispersed in the axial direction to form a series of focal points.…”