Abstract
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 Z-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 Ia and the invert normalized intensity ratio In, which is the inverse of Ia, is proposed to obtain the seamless relationship between the peak wavelength and the Z-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.
Highlights
Confocal microscopy [1,2] with a confocal probe has outstanding image formation properties in depth sectioning imaging and optical tomographic imaging [3,4,5], which makes it a potentially powerful tool for image formation in industrial and medical engineering fields, such as three-dimensional (3D)fine structure image formation [4,5] and living body observation of cells [6,7], compared with traditional microscopy
The dual-detector chromatic confocal probe has been designed to detect the axial position of a measurement target by using the normalized intensity ratio calculated from light intensities obtained by the two identical fiber detectors
For the expansion of the measurement range of the dual-detector chromatic confocal probe, invert normalized intensity ratio, which is the inverse of the normalized intensity ratio, has been employed to realize seamless measurement with the main-lobes and the side-lobes of the axial responses obtained from both the normalized intensity ratio and the invert normalized intensity ratio
Summary
Confocal microscopy [1,2] with a confocal probe has outstanding image formation properties in depth sectioning imaging and optical tomographic imaging [3,4,5], which makes it a potentially powerful tool for image formation in industrial and medical engineering fields, such as three-dimensional (3D). Employing a broadband laser source is another approach to expand the measurement range of a chromatic confocal probe [18,19], and several methods have been proposed so far. The proposed method has demonstrated that the influence of non-smoothness of the mode-locked femtosecond laser source can be compensated while expanding the measurement range over the whole spectrum of the laser by employing an axial response, defined as the intensity ratio of the two different confocal signals. As the second step of research, a new signal processing method for the axial response curve from the fiber-based dual-detector chromatic confocal probe with a mode-locked femtosecond laser source is proposed. In this paper, these annoying side-lobes are utilized to expand the measurement range of the dual-detector chromatic confocal probe with a mode-locked femtosecond laser source. Theoretical analysis and computer simulation, as well as some experiments, are carried out to demonstrate the feasibility of the proposed method for the extension of the measurement range
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