Mr. Sreeprasad Ajithaprasad Profile

Sreeprasad Ajithaprasad

at Indian Institute of Technology Kanpur

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Proceedings Article | 10 October 2020 Poster + Presentation + Paper

Demodulation of fringe patterns corrupted by non uniform intensity variations in dynamics studies

Allaparthi Venkata Satya Vithin, Issac Show, Sreeprasad Ajithaprasad, Gannavarapu Rajshekhar

Proceedings Volume 11552, 115521Z (2020) https://doi.org/10.1117/12.2584987

KEYWORDS: Fringe analysis, Demodulation, Signal to noise ratio, Phase measurement, Interferometry, Reflectivity, Metrology, Interference (communication), Graphics processing units, Analytical research

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Optical interferometric techniques have come to forefront in precision metrology applications such as surface profilometry, deformation analysis and defect testing. Reliable phase measurement from a recorded fringe pat- tern is the primary goal in most of these interferometric techniques. A primary constraint for accurate phase measurement is non uniform intensity fluctuations in fringe patterns caused by irregular illumination, uneven reflectivities and pixel defects. This problem is further aggravated in dynamics studies with multiple image capture where the intensity fluctuations can vary with time and thus lead to several fringe patterns getting affected. In this paper, this problem is investigated using the second order optimization framework along with the total variation regularization on a graphic processing unit (GPU). In our study, a series of fringe patterns are simulated with additive white Gaussian noise at signal to noise ratio of 20 dB. To induce fringe corruption due to the non uniform intensity conditions, the object wave amplitude is varied using an ellipse shaped filter which enables brighter conditions or stronger amplitudes inside the elliptical boundary and relatively darker conditions or weaker amplitudes outside of it. For time varying studies, we varied the size of the filter sequentially to gener- ate a series of interferograms with temporally varying non-uniform intensities. Further, orientations of elliptical illuminations are changed to verify the robustness of the algorithm. For processing a series of interferograms each with size of 512 by 512 pixels with dynamic range of 10 (ratio of brightest to darkest amplitude), we obtained root mean square error less than 0.25 radians for every interferogram using the proposed method. The results show that the proposed method is robust for handling non-uniform intensity corruptions in fringe patterns for dynamics based investigations.

Proceedings Article | 16 October 2019 Paper

A GPU assisted space frequency method for dynamic defect detection in optical metrology

Sreeprasad Ajithaprasad, Vigneshwar Rajendran, Rajshekhar Gannavarpu

Proceedings Volume 11205, 1120526 (2019) https://doi.org/10.1117/12.2541658

KEYWORDS: Fringe analysis, Defect detection, Interferometry, Fourier transforms, Optical metrology, Diffraction, Image processing

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The study of defect dynamics is an important problem in the field of non-destructive testing, crack propagation and fracture mechanics. Optical interferometric techniques are extensively used for this purpose because of their non-invasive behaviour and full field operation. The fringe patterns obtained from these techniques serve as good indicators for finding defects. In dynamic defect analysis, a large number of fringe patterns are captured and processed. The regions where the fringe density varies significantly are classified as defects. Thus, a fast, reliable and robust algorithm for identifying the rapid variations of fringe density is required. In this paper, we propose a graphics processing unit (GPU) assisted space frequency method based on windowed Fourier spectrum analysis for processing the dynamically varying fringe patterns. The main advantage of this approach is high computational efficiency achieved using GPU computing framework. The performance of the proposed method is demonstrated using 100 simulated fringe patterns, each of size 2048 x 2048 pixels. This large data stack was efficiently processed using the proposed method within only a minute, and thus, the proposed method offers the feasibility of high speed defect analysis. The practical application of the proposed method is explored by processing the fringe patterns obtained from the propagation of micron sized defects in an experimental configuration based on common-path diffraction phase microscopy setup.

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