Three simple and low-cost configurations of handheld scanning probes for optical coherence tomography have been developed. Their design and testing for dentistry applications are presented. The first two configurations were built exclusively from available off-the-shelf optomechanical components, which, to the best of our knowledge, are the first designs of this type. The third configuration includes these components in an optimized and ergonomic probe. All the designs are presented in detail to allow for their duplication in any laboratory with a minimum effort, for applications that range from educational to high-end clinical investigations. Requirements that have to be fulfilled to achieve configurations which are reliable, ergonomic—for clinical environments, and easy to build are presented. While a range of applications is possible for the prototypes developed, in this study the handheld probes are tested ex vivo with a spectral domain optical coherence tomography system built in-house, for dental constructs. A previous testing with a swept source optical coherence tomography system has also been performed both in vivo and ex vivo for ear, nose, and throat—in a medical environment. The applications use the capability of optical coherence tomography to achieve real-time, high-resolution, non-contact, and non-destructive interferometric investigations with micrometer resolutions and millimeter penetration depth inside the sample. In this study, testing the quality of the material of one of the most used types of dental prosthesis, metalo-ceramic is thus demonstrated.
Some forensic in situ investigations, such as those needed in transportation (for aviation, maritime, road, or rail accidents) or for parts working under harsh conditions (e.g., pipes or turbines) would benefit from a method/technique that distinguishes ductile from brittle fractures of metals-as material defects are one of the potential causes of incidents. Nowadays, the gold standard in material studies is represented by scanning electron microscopy (SEM). However, SEM instruments are large, expensive, time-consuming, and lab-based; hence, in situ measurements are impossible. To tackle these issues, we propose as an alternative, lower-cost, sufficiently high-resolution technique, Optical Coherence Tomography (OCT) to perform fracture analysis by obtaining the topography of metallic surfaces. Several metals have been considered in this study: low soft carbon steels, lamellar graphite cast iron, an antifriction alloy, high-quality rolled steel, stainless steel, and ductile cast iron. An in-house developed Swept Source (SS) OCT system, Master-Slave (MS) enhanced is used, and height profiles of the samples' surfaces were generated. Two configurations were used: one where the dimension of the voxel was 1000 µm 3 and a second one of 160 µm 3 -with a 10 µm and a 4 µm transversal resolution, respectively. These height profiles allowed for concluding that the carbon steel samples were subject to ductile fracture, while the cast iron and antifriction alloy samples were subjected to brittle fracture. The validation of OCT images has been made with SEM images obtained with a 4 nm resolution. Although the OCT images are of a much lower resolution than the SEM ones, we demonstrate that they are sufficiently good to obtain clear images of the grains of the metallic materials and thus to distinguish between ductile and brittle fractures-especially with the higher resolution MS/SS-OCT system. The investigation is finally extended to the most useful case of fatigue fracture of metals, and we demonstrate that OCT is able to replace SEM for such investigations as well.
We demonstrate the capability of optical coherence tomography (OCT) to perform topography of metallic surfaces after being subjected to ductile or brittle fracturing. Two steel samples, OL 37 and OL 52, and an antifriction Sn-Sb-Cu alloy were analyzed. Using an in-house-built swept source OCT system, height profiles were generated for the surfaces of the two samples. Based on such profiles, it can be concluded that the first two samples were subjected to ductile fracture, while the third one was subjected to brittle fracture. The OCT potential for assessing the surface state of materials after fracture was evaluated by comparing OCT images with images generated using an established method for such investigations, scanning electron microscopy (SEM). Analysis of cause of fracture is essential in response to damage of machinery parts during various accidents. Currently the analysis is performed using SEM, on samples removed from the metallic parts, while OCT would allow in situ imaging using mobile units. To the best of our knowledge, this is the first time that the OCT capability to replace SEM has been demonstrated. SEM is a more costly and time-consuming method to use in the investigation of surfaces of microstructures of metallic materials.
Choppers are optomechatronic devices used for the modulation of light: to attenuate or eliminate certain wavelength ranges or to generate series of laser impulses with different profiles. We have previously made a detailed study on choppers with rotating wheels with different configurations (with windows with linear and with non-linear margins) -and for different types of laser beams (i.e., top-hat, Gaussian and Bessel). In this paper we report a novel configuration of optical choppers with fast rotating elements (patent pending). The possible configurations of the device are discussed, and several chopper types are presented. The modulation functions of one of the types of choppers newly introduced (i.e., the functions of the transmitted flux) are deduced and studied with regard to the geometry of the device. Comparison with other types of choppers -classical and eclipse (the latter introduced by us) -are being made. Aspects like chop frequency, attenuation coefficient, and profile of the light impulses transmitted by the device are taken into account.
We present our experience regarding the establishing of an interdisciplinary group with Optics as one of its main topic at the Aurel Vlaicu University of Arad (UAVA) -linked with the improvement through research of our educational activities. The 3OM Group (in Opto-Mechatronics, Optical Metrology, and Optics & Mechanics) is described in its evolution from optomechanics to photonics, the latter with a focus on OCT (Optical Coherence Tomography) -with the national and the international collaborations established, with universities from Romania, Europe and USA. While the research directions of the 3OM Group are presented, they are linked with the educational components implemented in the various subjects we teach, for both undergraduate and graduate students, both in Mechanical and in Electrical Engineering. The main effort is to integrate education and research, to move teaching beyond the classical aspects to put the stress on hands-on-experiments, as well as on research-based activities -even with undergraduates. The main goals of this approach are to obtain an early orientation towards innovation and discovery, with a taste for novelties and with a clear focus on international standards. While this account is only one of many, it offers our experience in passing through the difficulties of developing both research and education in Optics in a young university in an emergent economy in Eastern Europe.
Forensic in situ investigations, for example for aviation, maritime, road, or rail accidents would benefit from a method that may allow to distinguish ductile from brittle fractures of metals -as material defects are one of the potential causes of such accidents. Currently, the gold standard in material studies is represented by scanning electron microscopy (SEM). However, SEM are large, lab-based systems, therefore in situ measurements are excluded. In addition, they are expensive and time-consuming. We have approached this problem and propose the use of Optical Coherence Tomography (OCT) in such investigations in order to overcome these disadvantages of SEM. In this respect, we demonstrate the capability to perform such fracture analysis by obtaining the topography of metallic surfaces using OCT. Different materials have been analyzed; in this presentation a sample of low soft carbon steel with the chemical composition of C 0.2%, Mn 1.15%, S 0.04%, P 0.05 % and Fe for the rest has been considered. An in-house developed Swept Source (SS) OCT system has been used, and height profiles have been generated for the sample surface. This profile allowed for concluding that the carbon steel sample was subjected to a ductile fracture. A validation of the OCT images obtained with a 10 microns resolution has been made with SEM images obtained with a 4 nm resolution. Although the OCT resolution is much lower than the one of SEM, we thus demonstrate that it is sufficient in order to obtain clear images of the grains of the metallic materials and thus to distinguish between ductile and brittle fractures. This study analysis opens avenues for a range of applications, including: (i) to determine the causes that have generated pipe ruptures, or structural failures of metallic bridges and buildings, as well as damages of machinery parts; (ii) to optimize the design of various machinery; (iii) to obtain data regarding the structure of metallic alloys); (iv) to improve the manufacturing technologies of metallic parts.
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