Recently, the industrial optical inspection has been a mainstream in measuring 2D images or 3D profiles of
microstructures. For the 3D profiling, the scanning white-light interferometer has a high resolution, but due to the
broadband light source, it has the low coherence length. Thus, it is very difficult to obtain the focused image with clear
interfered fringes, and the traditional auto-focusing approaches usually determine the wrong focused position. This paper
proposed a useful approach by the passive auto-focusing to determine the accurate focus for the scanning white-light
interferometers. Some experimental results are presented to verify the feasibility of the proposed approach.
3-D profilometry, it is necessary to locate the in-focus region of the image and to reconstruct the best 3D
profile. A series of images are collected on-the-fly. The contrast and the intensity indices of each region of
each image are calculated in the scanning procedure. The proposed method will reconstruct 3D shape from
moving platform. The proposed method is applied on some preliminary experiments and it shows that the
large-scale 3-D profile reconstruction can be realized.
This study proposes the auto-focusing procedure and the scan-range determining algorithm for white-light scanning
interferometry. During white-light scanning interferometry, the interference fringe must be located and to the best-focus
interferogram identified. The vertical-scan range must also be determined prior to the scanning procedure. A series of
images, either in-focus or out-of-focus, are collected in a proposed interference-fringe searching step. The contrast and
the sharpness indices of each image are calculated and applied in the auto-focusing scheme, and the vertical-scan range
is determined accordingly. Some preliminary experiments are performed to demonstrate that the best-focus
interferogram can be located precisely and the vertical-scan range can be determined.
A dynamic 3-D nano-scale surface profilometer using stroboscopic white light interferometry with novel image
deconvolution and automatic identification of structure resonant modes was successfully developed. As micro
electromechanical systems (MEMS) increase rapidly towards industrial application, the needs of accurate dynamic
characterization are extremely important to optimal design and fabrication. To meet the demands, an optical microscopy
based on stroboscopic interferometry was developed to achieve full-field vibratory out-of-plane surface profilometry
and system characterization. A novel deconvolution strategy with correction of the light response function was
established to remove the potential image blurs caused by the unavoidable vibration of the tested parts. With this
technical advance, the bandwidth of dynamic measurement can be significantly increased up to 10 MHz without
sacrificing measurement accuracy. Meanwhile, an innovative detection algorithm based on image contrast measure was
developed for automatic identification of accurate resonant modes. The detection method provides the simplest and
most economic way to detect accurate resonant peaks without adding any significant hardware in a stroboscopic
interferometric framework. To verify the effectiveness of the developed methodology, AFM cantilever beams were
measured to analyze the full-field resonant vibratory modes and dynamic characteristics. The experimental results
confirm that the resonant vibration behavior of the tested microcantilever beams can be accurately characterized and 5
nm of vertical measurement accuracy as well as tens micrometers of vertical measurement range can be achieved. The
measured results were satisfactorily consistent with the theoretical simulation outcomes from ANSYS.
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