Laser scanners with Risley prisms have the potential to perform a faster scanning in comparison to other twodimensional (2D) laser scanners, for example galvanometer-based. However, in contrast to the (constant speed) raster scanning produced by the latter, scan patterns of Risley prisms are highly non-linear, have intersection points, and are performed with variable speeds. The aim of this study is to build upon the novel, graphical method we have, to our knowledge, introduced for the study of these scan patterns. In contrast to complex analytical methods and to approximate ones, this graphical method is easy-to-apply and it provides exact scan patterns, respectively. In this study examples of experimental results are obtained to validate simulation results obtained using simple prisms equations and a commercially-available mechanical design program, CATIA V5 (Dassault Systèmes, Paris, France). Several characteristics of the laser scanner with a pair of rotational wedges are considered, with a focus on one of Marshall’s parameters, i.e. the ratio M of the rotational speeds of the prisms. An experimental validation is demonstrated for all characteristic graphs of the scan patterns for two pairs of values, M equals 2 or -2, as well as 8 and -8. The contrast between positive and negative values of M, as well as between lower and higher absolute values can be thus observed. As this is but a step in this study, directions of current work are also pointed out.
Risley prisms are utilized in a variety of applications, including precision pointing and scanning, interferometry, holography, polarimetry, and light attenuation. Laser scanning with such systems is fast, but the generated scan patterns are complicated. Analytical methods to determine them are rather difficult, while approximate methods do not provide exact patterns. While we point out these issues, the present study is built on a new, graphical method that, to our knowledge, we have introduced [V.-F. Duma, A. Schitea, Laser scanners with rotational Risley prisms: Exact scan patterns, Proc. of the Romanian Acad. Series A 19, 53-60, 2018] to obtain scan patterns produced by Risley prisms. A commercially available mechanical design program, CATIA V5R20 (Dassault Systèmes, Paris, France) has been used to perform the ray tracing, using the prisms equations, for all four possible configurations of laser scanners with a pair of rotational Risley prisms. One of these four configurations is considered in this study, to present the developed method. A deviation angle of 2° for the optical wedges is considered in this study. A brief comparison between the obtained exact scan patterns is made for different values of the parameter M (introduced by Marshall), which represents the ratio of the rotational speeds of the two prisms. The study also presents the cartesian coordinates of the points which define the trajectory of the laser spot on a scanned plane. Advantages of using the graphical method as well as its perspectives are pointed out.
Metals can break either in a ductile or brittle manner if a static or dynamic load is applied to the same material. This depends on a variety of factors, such as the manner in which the load is applied, the shape of the mechanical part, the operating conditions, the nature and structure of the metallic material, and the working temperature. If subjected to variable loads, metallic materials break due to what is called fatigue. The microscopic analysis of fracture surfaces is currently carried out by using scanning electron microscopy (SEM). We have proposed, for the first time to our knowledge, a new method to analyze fracture surfaces, using a low coherence interferometry technique, Optical Coherence Tomography (OCT) [Gh. Hutiu, V.-F. Duma, et al., Surface imaging of metallic material fractures using optical coherence tomography, Appl. Opt. 53, 5912-5916 (2014); Gh. Hutiu, V.-F. Duma, et al., Assessment of ductile, brittle, and fatigue fractures of metals using optical coherence tomography, Metals 8, 117 (2018)]. The present paper presents the way we have demonstrated that OCT can replace the gold standard in such assessments, i.e. SEM, despite the fact that OCT has a resolution of 20 to 4 μm (in our investigations), while the SEM we employed has a 4 to 2 nm resolution. A few examples are given in this respect–for different types of fractures. The advantages of OCT versus SEM are discussed. This development opens the way for in situ investigations, for example in forensic sciences, where OCT can be applied (including with handheld scanning probes. as we have developed). In contrast, SEM, TEM, and AFM are lab-based techniques, more expensive, and they require trained operators.
To determine the roughness is an important aspect in both industrial and biomedical applications. We propose and utilize for roughness evaluations, a non-destructive evaluation methods, Optical Coherence Tomography (OCT). For the metallic surfaces investigated from this point of view, the Ra and Rz parameters are utilized, according to ISO 4287/1988. Also, according to ISO 4280 and ISO 3274 standards, the measurements have been made on 12.5 mm portions. In order to accommodate such evaluations with the specific OCT field-of-view, four consecutive OCT images have been made for each sample, and an appropriate processing of the data collected from the surface profiles has been made. A validation of the results obtained with OCT has been completed with the gold standard for such evaluations, using a contact mechanical method, with a Mitutuyo profiler.