Abstract
Chromatic confocal microscopy (CCM) has been intensively developed because it can exhibit effective focal position scanning based on the axial chromatic aberration of broadband light reflected from a target. To improve the imaging speed of three-dimensional (3D) surface profiling, we have proposed the novel concept of swept-source-based CCM (SS-CCM) and investigated the usefulness of the corresponding imaging system. Compared to conventional CCM based on a broadband light source and a spectrometer, a swept-source in the proposed SS-CCM generates light with a narrower linewidth for higher intensity, and a single photodetector employed in the system exhibits a fast and sensitive response by immediately obtaining spectrally encoded depth from a chromatic dispersive lens array. Results of the experiments conducted to test the proposed SS-CCM system indicate that the system exhibits an axial chromatic focal distance range of approximately 360 for the 770–820 nm swept wavelength range. Moreover, high-speed surface profiling images of a cover glass and coin were successfully obtained with a short measurement time of 5 ms at a single position.
Highlights
Three-dimensional (3D) surface imaging is becoming increasingly important in various fields, such as the surface defect testing of tiny electronic components or measuring the 3D structure of living cells; a fast and accurate surface profiling technique is in high demand [1,2,3,4]
The confocal microscopy (CCM) uses chromatic aberration of the lens to generate light dispersion depending on wavelength, causing each wavelength to correspond to a different focal distance
In this paper, we have proposed a novel configuration of swept-source-based chromatic confocal microscopy (SS-CCM) and demonstrated its excellent sensitivity and fast measurement speed simultaneously [17]
Summary
Three-dimensional (3D) surface imaging is becoming increasingly important in various fields, such as the surface defect testing of tiny electronic components or measuring the 3D structure of living cells; a fast and accurate surface profiling technique is in high demand [1,2,3,4]. Compared to interferometric OCT imaging with a low numerical aperture (NA) lens, CM can provide a higher axial and lateral resolution if a high-NA lens and a limited depth of focus from a pinhole are used [8]. Despite these advantages, CM has suffered from imaging speed limitations due to its mechanical scanning process for the lateral and axial directions, and there have been many attempts to improve its scanning speed. The focal distance of the lens is spectrally encoded, and the relative depth of Sensors 2020, 20, 7347; doi:10.3390/s20247347 www.mdpi.com/journal/sensors
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