LOW-COHERENCE INTERFEROMETRY SYSTEM AND ITS APPLICATION FOR CONTACTLESS PROFILOMETRY AND OPTICAL COHERENCE TOMOGRAPHY
An experimental model of the low-coherence interferometry system has been designed and investigated. An important feature of the model is that it allows using micro objectives of different magnification to vary the optical resolution and the field of view. The model is versatile due to micro objectives with different mounting threads, several kinds of radiation sources (LED or SLD) as well as tubular lenses of different focal length. The optical system configuration is scalable, as the length of its arms can be altered by adding rod fixtures. It is possible to optimize the system operational modes from the viewpoint of resolution and speed when investigating a variety of object categories like layered media, scattering media, including biological tissues.
The model was employed to investigate experimentally the parameters of data registration in asynchronous scanning mode as well as to optimize the resolution/speed ratio. The signal-to-noise ratio and the information criterion were used for such optimization.
The low coherence fringe signals were analyzed involving the stochastic systems and signals theory, namely, by the adaptive Wiener filter (WF), and the Kalman filter (KF). Characteristics of an adaptive WF were investigated when the WF involves small number of simultaneously processed samples (three samples), an a priori unknown signal discretization step and significant changes of the background (incoherent) signal component as affected by the observation conditions. The researchers were thus able to determine the envelope of interferometric vector signals obtained by co-processing a set of A-scans. The algorithm was proven to provide high noise-immunity when evaluating the interference fringes envelope and the actual discretization step of the interferometric signal phase using the obtained adaptive WF coefficients to minimize the error variance in relation to the generated reference signal.
The experimental results of the designed system application for contactless profilometry and time-domain optical coherence tomography when investigating various objects including multilayer semitransparent objects are presented.
The work was financially supported by the Russian Science Foundation (Grant No. 19-79-10118).
Maxim A. Volynsky
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