Olga M. Conde

Comparison between a symmetric bidirectional-pumping and a unidrectional-pumping configurations in an erbium fiber ring laser

An experimental comparative study between two wide-band wavelength-tunable erbium doped fiber ring lasers (EDFRLs) with the same active fiber length but with two different pumping configuration (forward unidirectional pumping and symmetric bidirectional pumping) is reported in this paper. Both fiber lasers cover almost the whole C-band and L-band with a single setup laser. The signal wavelength can be tuned in a wide range of 60 nm with the two presented lasers. Nevertheless, experimental results verify that a higher output power is obtained with the bidirectional pump configuration.

Pulse shape effects on the measurement of temperature using a Brillouin-based optical fiber sensor

Distributed fiber sensing based on Brillouin gain scattering (BGS) principle is a useful way to develop devices capable to measure temperature or/and strain in optical fibers. New effects or technologies that could achieve a larger distance and/or a better spatial resolution are a topic of special interest in this fiber sensing area. The influence of the probe-pulse shape in the interaction between the pulsed light and the continuous wave laser in a pump-probe system is presented. The purpose of this study is to improve the spatial resolution of the measurement without losing stability in the BGS. Also it is showed how the backscattering Brillouin gain is affected by inducing variations on the final value of the BGS intensity; this effect is illustrated by using an experimental set up based on the Brillouin optical time-domain analysis (BOTDA). Theoretical analysis of the probe pulse in the Brillouin shift and intensity value using triangular, sinc and saw tooth shapes around the medium phonon life time (~10ns) are presented; as well as the experimental results and possible applications are explained.

Spectroscopic analysis technique for arc-welding process control

The spectroscopic analysis of the light emitted by thermal plasmas has found many applications, from chemical analysis to monitoring and control of industrial processes. Particularly, it has been demonstrated that the analysis of the thermal plasma generated during arc or laser welding can supply information about the process and, thus, about the quality of the weld. In some critical applications (e.g. the aerospace sector), an early, real-time detection of defects in the weld seam (oxidation, porosity, lack of penetration, ...) is highly desirable as it can reduce expensive non-destructive testing (NDT). Among others techniques, full spectroscopic analysis of the plasma emission is known to offer rich information about the process itself, but it is also very demanding in terms of real-time implementations. In this paper, we proposed a technique for the analysis of the plasma emission spectrum that is able to detect, in real-time, changes in the process parameters that could lead to the formation of defects in the weld seam. It is based on the estimation of the electronic temperature of the plasma through the analysis of the emission peaks from multiple atomic species. Unlike traditional techniques, which usually involve peak fitting to Voigt functions using the Levenberg-Marquardt recursive method, we employ the LPO (Linear Phase Operator) sub-pixel algorithm to accurately estimate the central wavelength of the peaks (allowing an automatic identification of each atomic species) and cubic-spline interpolation of the noisy data to obtain the intensity and width of the peaks. Experimental tests on TIG-welding using fiber-optic capture of light and a low-cost CCD-based spectrometer, show that some typical defects can be easily detected and identified with this technique, whose typical processing time for multiple peak analysis is less than 20msec. running in a conventional PC.

OCT inspection of degenerative and rheumatic tendinous cords

Surgical repair of the mitral valve complex presents high mortality rates, strongly dependent on the surgical procedure. Intensity and polarization sensitive OCT are explored as a feasible degradation inspection method for rheumatic and degenerative chords.

Iterative Otsu's method for OCT improved delineation in the aorta wall

Degradation of human ascending thoracic aorta has been visualized with Optical Coherence Tomography (OCT). OCT images of the vessel wall exhibit structural degradation in the media layer of the artery, being this disorder the final trigger of the pathology. The degeneration in the vessel wall appears as low-reflectivity areas due to different optical properties of acidic polysaccharides and mucopolysaccharides in contrast with typical ordered structure of smooth muscle cells, elastin and collagen fibers. An OCT dimension indicator of wall degradation can be generated upon the spatial quantification of the extension of degraded areas in a similar way as conventional histopathology. This proposed OCT marker can offer in the future a real-time clinical perception of the vessel status to help cardiovascular surgeons in vessel repair interventions. However, the delineation of degraded areas on the B-scan image from OCT is sometimes difficult due to presence of speckle noise, variable signal to noise ratio (SNR) conditions on the measurement process, etc. Degraded areas can be delimited by basic thresholding techniques taking advantage of disorders evidences in B-scan images, but this delineation is not optimum in the aorta samples and requires complex additional processing stages. This work proposes an optimized delineation of degraded areas within the aorta wall, robust to noisy environments, based on the iterative application of Otsu’s thresholding method. Results improve the delineation of wall anomalies compared with the simple application of the algorithm. Achievements could be also transferred to other clinical scenarios: carotid arteries, aorto-iliac or ilio-femoral sections, intracranial, etc.

Optical Methods for On-line Quality Assurance of Welding Processes in Nuclear Steam Generators

The manufacturing of steam generators relies heavily in many different processes of welding, involving a wide range of materials, welding procedures and requirements. Quality assurance is of paramount importance in these processes, and in the case of the nuclear industry, even more rigorous quality control procedures, according to the nuclear safety regulatory rules and customer specifications, are required. The currently accepted procedure for quality control is based on the rigorous control of the welding parameters, such as the heat input, welding speed, material geometry, surface preparation and cleanness, etc. However, it is known that the physics involved in these processes is extremely complex, and the efforts aimed at developing a reliable formulation of the relationships between the process parameters and a defect-free welding seam have mostly failed (Wu et al., 1997), with only some success in the prediction of stress and distortion of the joined piece (Dong, 2005). For that reason, quality assurance in welding processes is typically performed by means of procedure trials, where the suitable welding parameters are established and used later in production. However, as there is no guarantee that a free-defect welding is always achieved, non-destructive testing (NDT) techniques are routinely applied in different stages of the manufacturing process. These techniques (liquid penetrant, magnetic-particle, ultrasonic, XRay, Eddy current testing ...) are quite effective to validate the quality of the welds, but most of them are difficult to automate, require complex procedures and take a significant amount of the production time. Although off-line NDT procedures can not be avoided in those critical applications, there is still a great interest in the possibility of on-line monitoring and control of the welding process. This approach allows the early repair (or even the real-time correction) of defects, resulting in a reduction of the manufacturing time and costs. This paper deals with one particular approach for on-line sensing, namely, the spectroscopic detection and processing of the light generated by the process itself. A great deal of information about the real-time behaviour of the welding process can be extracted through

Welding diagnostics by means of line-to-continuum method and SFFS spectral band selection

Plasma optical spectroscopy is a technique widely used for on-line welding diagnostics, given the rich information to be found within the plasma spectra generated during the process. One of the key factors in this regard is the computational performance of the whole monitoring system, as it determines the resulting spatial resolution. The electronic temperature of the welding plasma is typically used as the output monitoring parameter, but it requires an identification of the emission lines, what implies additional processing stages. In this paper we propose the use of the line-to-continuum method to generate the system output profiles, previously choosing the required spectral band by means of the SFFS algorithm.

Comparative analysis of quality parameters of Italian extra virgin olive oils according to their region of origin

Italian extra virgin olive oils from four regions covering different latitudes of the country were considered. They were analyzed by means of absorption spectroscopy in the wide 200-2800 nm spectral range, and multivariate data processing was applied. These spectra were virtually a signature identification from which to extract information on the region of origin and on the most important quality indicators. A classification map was created which was able to group the 80 oils on the basis of their region of origin. Furthermore, a model for the prediction of quality parameters such as oleic acidity, peroxide number, K232, K270 and Delta K, was developed.