Thickness Measurement for Glass Slides Based on Chromatic Confocal Microscopy with Inclined Illumination

Abstract

Chromatic confocal microscopy is a widely used method to measure the thickness of transparent specimens. In conventional configurations, both the illumination and imaging axes are perpendicular to the test specimen. The reflection will be very weak when measuring high-transparency specimens. In order to overcome this limitation, a special chromatic confocal measuring system was developed based on inclined illumination. This design was able to significantly improve the signal-to-noise ratio. Compared with conventional designs, the proposed system was also featured by its biaxial optical scheme, instead of a coaxial one. This biaxial design improved the flexibility of the system and also increased the energy efficiency by avoiding light beam splitting. Based on this design, a prototype was built by the authors’ team. In this paper, the theoretical model of this specially designed chromatic confocal system is analyzed, and the calculating formula for the thickness of transparent specimen is provided accordingly. In order to verify its measurement performance, two experimental methodology and results are presented. The experimental results show that the repeatability is better than 0.54 μm, and the axial measurement accuracy of the system could reach the micron level.

Osteoimmunomodulatory Gelma/ Liposome Coatings to Promote Bone Regeneration of Orthopedic Implants

“…The coating thicknesses were measured by confocal microscopy. The transparent hydrogel containing fluorescent dyes can be detected with this method [41]. The GelMA containing FITC and Rh-PE labelled Lip were electrosprayed on the implant surfaces.…”

Monochromatic LED-based spectrally tunable light source for chromatic confocal sensors

“…Widespread applications include measuring the thickness of transparent materials and the three-dimensional topography of object surfaces. [1][2][3] The axial measuring range of CCS is determined by the combination of the spectral bandwidth of the light source and the dispersion capabilities of the dispersive objective. Therefore, a suitable light source is essential for the construction of high-performance CCS.…”

“…Chromatic confocal sensor (CCS) employs a specially constructed dispersive objective lens to focus light of different wavelengths from a broad-spectrum light source at various points along the optical axis, therefore expanding the axial measurement range. Widespread applications include measuring the thickness of transparent materials and the three-dimensional topography of object surfaces 1 – 3 The axial measuring range of CCS is determined by the combination of the spectral bandwidth of the light source and the dispersion capabilities of the dispersive objective.…”

“…Prior art light sources include the halogen tungsten lamp, 1 the xenon lamp, 5 the “white” light-emitting diode (LED), 6 and the supercontinuum light source 7 – 9 As typical wide-spectrum light sources, tungsten halogen lamps and xenon lamps can offer high-brightness, wide-spectrum lighting that satisfies the technical criteria of CCS.…”

Bilateral form characterization of curved transparent components using chromatic confocal sensor

“…Previous researchers have investigated lower surface distance measurement methods for transparent plane-parallel plates and lenses based on the chromatic confocal sensor 16 , 17 . Various novel modified models have also been proposed for precision measurements of the lower surface profile of thin transparent components, e.g., frequency-shifted confocal feedback, 18 adaptive modal decomposition, 19 biaxial optical scheme with inclined illumination, 20 and so on 21 , 22 . But these methods are only applicable to plane-parallel plates, and there is still non-negligible error when it comes to curved components.…”