Category: NDE/NDT

We present the use of sub-micron resolution optical coherence tomography (OCT) in quality inspection for printed electronics. The device used in the study is based on a supercontinuum light source, Michelson interferometer and high-speed spectrometer. The spectrometer in the presented spectral-domain optical coherence tomography setup (SD-OCT) is centered at 600 nm and covers a 400 nm wide spectral region ranging from 400 nm to 800 nm. Spectra were acquired at a continuous rate of 140,000 per second. The full width at half maximum of the point spread function obtained from a Parylene C sample was 0:98 m. In ...

The increasing demand of the aerospace industry for new functional materials requires appropriate methods for quality assessment. It is a new challenge nowadays to characterize materials with microstructure quickly, accurately, and nondestructively. Optical coherence tomography (OCT) is a contactless and non-destructive technique for obtaining the internal structure of turbid materials. In the past 20 years it has been continuously developed and nearly exclusively applied for biomedical imaging of tissues while OCT-based methods for non-biomedical investigation tasks, e.g. within the field of non-destructive testing for material inspection, are rarely reported. Therefore, here we demonstrate and evaluate the suitability of OCT ...

We demonstrate tomographic and volumetric reconstruction of composite material using a full-field swept-source optical coherence tomographic (FF-SS-OCT) system. The FF-SS-OCT system is based on a co-axial and common-path optical interferometric system based on Mirau objective lens. By means of sweeping the frequency of the broad-band light source, multiple spectral interferograms are recorded and stacked in the X–Y–λ axes and processed in a computer. Optically sectioned images of the composite material at different depths are reconstructed. From the spectral interference fringe signal, the phase maps at various depths are also reconstructed. Due to its common path configuration, the present ...

Polymeric fixed partial prosthesis represents an important part of the prosthetic treatment. Their presence in the oral cavity could lead to fracture them and to alter the final prosthetic treatment. Time Domain Optical Coherence Tomography can be used as a noninvasive evaluation method and 3D reconstructions which could generate a real forecast on those prosthesis in the oral cavity environment.

Large-scale and cost-effective manufacturing of ceramic micro devices based on tape stacking requires the development of inspection systems to perform high-resolution in-process quality control of embedded manufactured cavities, metal structures and defects. With an optical coherence tomography (OCT) system operating at 1.3 μm and a dedicated automated line segmentation algorithm, layer thicknesses can be measured and laser-machined channels can be verified in alumina ceramics embedded at around 100 μm depth. Monte Carlo simulations are employed to analyze the abilities of OCT in imaging of the embedded channels. The light scattering parameters required as input data for simulations are evaluated ...

Mechanical material testing combined with optical coherence tomography (OCT) allows for the first time the immediate detection of inner structural changes along with a qualitative observation of the local strain distribution in surface near bulk regions of semitransparent and translucent specimens. In addition to a 3D full field strain analysis (FFSA) system based on digital image correlation (DIC), a customized spectral domain OCT system operating at 1550 nm was applied for investigation. Exemplified by tensile testing of elastomer particle filled polypropylene specimens, local dissimilarity evaluation of the OCT images was performed. The results show the high potential of OCT to ...

An experimental evaluation of reduced scattering coefficient in a homogeneous scattering medium is presented. For deriving the reduced scattering coefficient, a scattering coefficient in a weak scattered region is measured by optical coherence tomography and an anisotropic parameter is derived from the measurement of output beam width. The experimental results showed that the proposed method gave the acceptable values by comparing the results from Mie theory.

The Technical University of Denmark (DTU) has demonstrated the first application of optical coherence tomography (OCT) as a 3-dimensional (3D) imaging technique to visualize the internal structure of complete multilayered polymer solar cell modules. The work has been carried out in a cross-disciplinary collaboration between DTU Fotonik/Department of Photonics Engineering and Risø National Laboratory for Sustainable Energy, both part of DTU.The 3D imaging of complete polymer solar cells prepared by roll-to-roll coating was carried out using a high-resolution 1322nm OCT system having a 4.5 microns axial resolution and a 12 microns lateral resolution. It was possible to ...

A common-path swept-source optical coherence tomography (SS-OCT) is a promising scheme for implementing a high-speed and stable OCT system. We investigate the capability of a common-path SS-OCT system to perform the cross-sectional imaging of valuable documents translated at high speed for the check of its security feature. The influence of transport speeds, up to 2000 mm/s, on the depth resolution and the signal intensity is experimentally evaluated using a SS-OCT system equipped with a swept source at a center wavelength of 1335 nm and with a sweep repetition rate of 50 kHz. The degradation of the measured signal is ...

We demonstrate that polarization-sensitive optical coherence tomography (PS-OCT) is suitable to map the stress distribution within materials in a contactless and non-destructive way. In contrast to transmission photoelasticity measurements the samples do not have to be transparent but can be of scattering nature. Denoising and analysis of fringe patterns in single PS-OCT retardation images are demonstrated to deliver the basis for a quantitative whole-field evaluation of the internal stress state of samples under investigation.

The 3-dimensional imaging of complete polymer solar cells prepared by roll-to-roll coating was carried out using high-resolution 1322 nm optical coherence tomography (OCT) system. We found it possible to image the 3-dimensional structure of the entire solar cell that comprises UV-barrier, barrier material, adhesive, substrate and active solar cell multilayer structure. The achievable resolution was 12 μm in the lateral plane and 4.5 μm in the depth. We found that the OCT technique could be readily employed to identify coating defects in the functional layers. We finally identify the limitations of the technique, and future developments that would strengthen ...

We will show how optical coherence tomography (OCT) can be used as a tool for non-destructive testing and evaluation of painted metallic materials. This technique is particularly suited for highly scattering material due to the gated nature of OCT.

We present the application of ultra-high resolution optical coherence tomography (UHR-OCT) in evaluation of thin, protective films used in printed electronics. Two types of sample were investigated: microscopy glass and organic field effect transistor (OFET) structure. Samples were coated with thin (1–3 μm) layer of parylene C polymer. Measurements were done using experimental UHR-OCT device based on a Kerr-lens mode locked Ti:sapphire femtosecond laser, photonic crystal fibre and modified, free-space Michelson interferometer. Sub-micron resolution offered by the UHR-OCT system applied in the study enables registration of both interfaces of the thin encapsulation layer. Complete, volumetric characterisation of protective ...

Optical coherence tomography (OCT) is a non-invasive analysis technique allowing fast and high-quality cross-sectional imaging of scattering media. OCT is based on the physical phenomenon of low coherence interferometry and is thus well suited to image layered structures. In this paper, high-speed spectral domain OCT was used for the characterization of pharmaceutical tablet coatings, sampled at different stages of an industrial drum spray coating process, comprising tablets with a coating thickness ranging from uncoated to a target coating thickness of about 70 μm. In addition to the OCT investigation of layer thickness and homogeneity, tablet weight gain and tablet diameters ...

Researchers at Gwangju Institute of Science and Technology in Korea continue to explore a wide variety technologies and applicatoins of OCT including some very interesting non-medical applications of OCT. This includes some recent work in collaboration with Western Digital Corporation, one of the world's leading manufacturer of hard disc drives, where full-field optical coherence tomography was used to investigate the surface of wet pads used in chemical mechanical polishing of silicon wafers.For more information see recent Article. Courtesy Woo June Choi.