Use of two wavelengths in microscopic TV holography for nondestructive testing

Abstract

Single wavelength TV holography is a widely used whole-field noncontacting optical method for nondestructive testing (NDT) of engineering structures. However, with a single wavelength configuration, it is difficult to quantify the large amplitude defects due to the overcrowding of fringes in the defect location. In this work, we propose a two wavelength microscopic TV holography using a single-chip color charge-coupled device (CCD) camera for NDT of microspecimens. The use of a color CCD allows simultaneous acquisition of speckle patterns at two different wavelengths and makes the data acquisition as simple as that of the single wavelength case. For the quantitative measurement of the defect, an error compensating eight-step phase-shifted algorithm is used. The design of the system and a few experimental results on small-scale rough specimens are presented. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)

Phase shifting white light interferometry using colour CCD for optical metrology and bio-imaging applications

“…Three different sensors have been used for recording colour interferogram: (a) 1-CCD sensor with Bayer filter, [22] (b) 3-CCD sensor, [25] and (c) Foveon X3 sensor. [29] The Bayer filter 1-CCD RGB camera has been demonstrated for many applications including: surface profiling of large discontinuities, [28] simultaneous measurement of shape and deformation, [27,30] nondestructive testing (NDT) of large defects, [31] simultaneous acquisition of blood flow, blood volume, and oxygenation on human fingers using dual-wavelength laser imaging [32] etc. Recently, white light illumination combined with single-chip CCD RGB camera was successfully demonstrated for surface profiling of micro-lens array and large-discontinuities, [33] refractive index profiling of biological cells (RBCs), [26] onion skin, [34] fish-eye cornea [35] etc.…”

Multi-colour microscopic interferometry for optical metrology and imaging applications

“…In multi-colour interferometry, the light source is tunable or broad band and the detector is a colour CCD camera. Several configurations have been reported with colour CCD cameras : 2λ-interferometry with a 1-CCD [47,60], 3λ-interferometry with 1-CCD [48]and 3-CCD [49], and white light interferometry with 1-CCD [50,53,78]and 3-CCD [49,63]. A typical system based on white light illumination and a 1-CCD colour camera is depicted in Fig.4 [30,53].…”

“…Two-wavelength speckle fringe analysis for quantifying large defects was demonstrated [60,102]. Experiments were conducted on a flat 4 X 3 mm 2 specimen with a simulated defect in 1 mm 2 area.…”

“…The Bayer filter 1-CCD RGB camera has been demonstrated for surface profiling of large discontinuities [23,51,58,59], and simultaneous measurement of shape and deformation [23,48], non-destructive testing (NDT) of large defects [60], simultaneous acquisition of blood flow, blood volume, and oxygenation on human fingers using dualwavelength laser imaging [61]etc. Recently, white light illumination combined with 1-CCD RGB camera was successfully demonstrated for surface profiling of micro-lens array and large-discontinuities [30], biological cells such as human Red-Blood-Cell (RBCs) [21,50,62], onion skin/cells [22], fish-eye cornea [55]etc.…”

“…The 3-D view of the defect is in Fig.15(i) which clearly shows the enhanced defect. Thus the two-wavelength analysis allows quantification of large defects and also it can provide the shape of the test object at effective wavelength[60,102].…”