Abstract
The two peaks characteristic of yellow and blue light in the spectrum of dual-wavelength white light emitting diodes (LEDs) introduce distinctive features to the interference signal of white light scanning interferometry (WLSI). The distinctive features are defined as discontinuities, so that the fringe contrast function cannot be modeled as a single Gaussian function, and causes the interferogram to have uneven distribution of fringes of different orders in the scanning interferometer. This phenomenon leads to the low accuracy of the zero-order fringe position in the envelope calculation, which affects the repeatability and accuracy of the interferometry. This paper proposes a new surface recovery algorithm based on the Hilbert phase envelope and adjacent reference points calculation, which can effectively overcome the influence of the discontinuous signal of dual-wavelength LED white light interference on the three-dimensional reconstruction of WLSI measurements. The reliability of the algorithm is verified by experiments, and the measurement accuracy of LED WLSI system is evaluated.
Highlights
White-light scanning interferometry (WLSI) is an established optical method for surface profile measurement by analyzing a series of interference patterns of low coherence light with known optical path differences among them
The spatial distance between the surface measurement point and the equal optical path point can be obtained by collecting the interference fringes with charge coupled device (CCD) and calculating the position of the signal coherence peak, so as to realize the height recovery of the measurement surface with nanometer resolution [1,2]
The brightness of the light source in WLSI can affect the contrast of interference fringes, and its spectral width is related to the area where interference occurs
Summary
White-light scanning interferometry (WLSI) is an established optical method for surface profile measurement by analyzing a series of interference patterns of low coherence light with known optical path differences among them. Due to the asymmetric interference signal characteristics and the problem of phase mutation, LED WLSI often has poor reconstruction quality To solve this problem, Wee Keat Chong [5,12,13] proposed a local Gaussian fitting method to reduce the impact of LED dual-wavelength, and proposed to perform band-pass filtering on the two peaks after Fourier transform of the LED spectrum, and obtain the phase information for each filter window. The reference height of the adjacent phase reference point is calculated, and the difference between the initial solution height and the reference height is compared to optimize the surface reconstruction result This algorithm effectively decreases the negative impact caused by double peaks characteristic of the light source spectrum in the surface reconstruction for the LED WLSI, and solve the problems of envelope peak extraction inaccuracy and the difficulty of solving the phase mutation in the traditional algorithm to a certain extent. Influence Analysis of Dual-Wavelength White LED Spectrum on Interference Signal
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