René Héon

An evaluation of a commercial Échelle spectrometer with intensified charge-coupled device detector for materials analysis by laser-induced plasma spectroscopy ☆

Abstract In this work we evaluate the performance of a commercial Echelle spectrometer coupled with an intensified charge-coupled device (ICCD) detector for the analysis of solid samples by laser-induced plasma spectroscopy (LIPS) in air at atmospheric pressure. We compare results obtained in aluminum alloy samples with this system and with a ‘conventional’ Czerny-Turner spectrometer coupled to an intensified photodiode array (IPDA). We used both systems to generate calibration curves and to determine the detection limit of minor elements, such as Mg, Cu, Si, etc. Our results indicate that no significant differences in terms of analytical figures of merit exist between the Echelle/ICCD system and a conventional Czerny-Turner spectrometer with IPDA. Moreover, measurements of plasma temperature and electron density using the two assemblies give, in general, very similar results. In the second part of this work, we aim to present a critical view of the Echelle spectrometer for LIPS applications, by drawing up the balance sheet of the advantages and limitations of the apparatus. The limitations are either inherent to the dispersion method, or result from the dynamic range of the detector. Moreover, the minimum ICCD readout time does not allow a fast data acquisition rate. On the other hand, the Echelle spectrometer allows complete elemental analysis in a single shot, as spectral lines of major, minor and trace constituents, as well as plasma parameters, are measured simultaneously. This enables a real-time identification of unknown matrices and an improvement in the analytical precision by selecting several lines for the same element.

Broadband optical detection of ultrasound by optical sideband stripping with a confocal Fabry-Perot

A method which allows broadband optical detection of ultrasound with large etendue from a scattering surface is presented. The wave scattered by the surface interferes with a reference wave which is derived from the scattered wave after stripping it from its optical sidebands by a confocal resonator. Simple implementation by a confocal Fabry–Perot used in reflection is explained and demonstrated experimentally.

Laser optical ultarasound detection using two interferometer systems

A laser ultrasound detection technique which is insensitive to laser intensity fluctuations, perturbation at the object surface and the like is disclosed. The invention consists of two substantially identical interferometers of the Fabry-Perot type or such an interferometer with a birefringent element in its optical cavity. The interferometers have resonance frequencies higher and lower than the laser frequency so that noises can be cancelled out by signal processing.

Laser-Ultrasonics: From the Laboratory to the Shop Floor

Ultrasonics is a powerful technique for inspecting and characterizing industrial materials. It not only can detect bulk and surface flaws, but also obtain information on material microstructure, which determines engineering properties, such as elastic moduli and ultimate strength. However, traditional ultrasound requires liquid or contact coupling for its generation and detection, making it difficult or impossible to apply in many industrial situations. This occurs, in particular, on curved parts and on parts at elevated temperature, a situation widely found in industrial products and during the processing of industrial materials.Through a continuing effort that started more than 10 years ago, the Industrial Materials Institute of the National Research Council of Canada working in collaboration with UltraOptec Inc. has developed a technique called laser-ultrasonics, that circumvents the limitations of the conventional techniques. This novel technique is based on the generation and detection of ultrasound with lasers. The technology we have developed has been demonstrated to be applicable to real industrial conditions. In particular, a system was brought to a steel mill to measure on-line the wall thickness of tubes at 1000°C moving at 4 m/s. The capability of our technology to inspect advanced aircrafts made of composite materials was also demonstrated by inspecting a CF-18 in the hangar of a maintenance facility. UltraOptec Inc. is now in the process of commercializing this technology, in particular, for these two demonstrated industrial applications.

Influence of Er:YAG and Nd:YAG wavelengths on laser-induced breakdown spectroscopy measurements under air or helium atmosphere

Laser-induced breakdown spectroscopy (LIBS) is widely dependent on the conditions of its implementation in terms of laser characteristics (wavelength, energy, and pulse duration), focusing conditions, and surrounding gas. In this study two wavelengths, 1.06 and 2.94 microm, obtained with Nd:YAG and Er:YAG lasers, respectively, were used for LIBS analysis of aluminum alloy samples in two conditions of surrounding gas. The influence of the laser wavelength on the laser-produced plasma was studied for the same irradiance by use of air or helium as a buffer gas at atmospheric pressure. We used measurements of light emission to determine the temporally resolved space-averaged electron density and plasma temperature in the laser-induced plasma. We also examined the effect of laser wavelength in two different ambient conditions in terms of spectrochemical analysis by LIBS. The results indicate that the effect of the surrounding gas depends on the laser wavelength and the use of an Er:YAG laser could increase linearity by limiting the leveling in the calibration curve for some elements in aluminum alloys. There is also a significant difference between the plasma induced by the two lasers in terms of electron density and plasma temperature.

Laser-Ultrasonics for Industrial Applications

Increased use of advanced materials and more stringent requirements for process and quality control are creating new needs for nondestructive inspection techniques. Ultrasonics is a widely used technique for defect detection in various materials and is being developed, and even in some cases actually applied for microstructural characterization. However, ultrasonics in its present state of implementation in industry suffers several limitations. Probing materials at elevated temperature is made difficult by fluid coupling problems. Inspecting specimens of complex shapes requires sophisticated robotic manipulators to properly orient the transducer. Furthermore, since the technique relies on a piezoelectric resonator to generate and receive ultrasound, it does not have the adequate bandwidth or sensitivity for some applications.

Laser-Ultrasonic Inspection of the Composite Structure of an Aircraft in a Maintenance Hangar

Composite materials used in aerospace structures can be affected by a variety of defects, such as delaminations and disbonds, which may occur during fabrication or may be caused by impact during use. Such defects, which cannot usually be detected by simple visual inspection, may severely affect the mechanical integrity of components. Ultrasonics offers the best possibility for detection of flaws in composite components. However, ultrasonics as conventionally applied using piezoelectric transducers for generation and detection of the probing pulse has several limitations. Namely, the need for an acoustic coupling media or direct contact with the surface, and the requirement of near-normal incidence to the component’s surface. Laser-ultrasonics represents a practical means of avoiding the inherent difficulties with conventional ultrasonics [1–2].

REMOTE THICKNESS MEASUREMENT OF OIL SLICKS ON WATER BY LASER-ULTRASONICS

ABSTRACT At the National Research Council of Canada Industrial Materials Institute, research is in progress on the application of laser-ultrasonics to remote measurement of the thickness of oil on ...

Laser Ultrasonic Inspection of Graphite Epoxy Laminates

Superior mechanical properties and reduced weight of fiber reinforced polymer matrix composite laminates (e.g., made of graphite epoxy) are leading to their increased use in aeronautic and aerospace structures. These materials are found more and more in load bearing components, which in turn, requires their integrity to be fully evaluated by nondestructive inspection. This applies to newly manufactured parts which can be flawed following improper manufacturing procedures and to parts which have been in service on an aircraft as well, since additional flaws could have occurred and old existing flaws could have grown and become more severe. Flaws which are found in these materials include porosity and foreign inclusions, which are produced during manufacturing and delaminations between plies, which can be produced at manufacturing or can be caused by the impact of foreign objects on the structure. Ultrasonics has been recognized to be a superior technique for detecting delaminations and can be used to detect foreign inclusions and assess porosity, as well [1,2]. The ultrasonic waves are usually generated and detected by piezoelectric transducers and coupled to the inspected part by direct contact or water. Although operation in transmission is widely used and easily implemented for curved parts, the pulse-echo mode is preferred since it requires only single side access and provides flaw depth information. In this case, the transducer should be properly aligned with respect to the surface of the inspected part (within a few degrees), since it is a phase sensitive device emitting and its whole surface.

Laser ultrasonic inspection of honeycomb aircraft structures

Ultrasonic methods have been used extensively for the inspection of advanced composite materials and adhesively bonded structures. Conventional ultrasonic inspections usually require couplants to propagate ultrasonic waves to and from the part surface. Delaminations, porosities, and foreign inclusions in composite laminates can be successfully detected by pulsed-echo and through-transmission modes of ultrasonic inspection. Debonds in adhesively bonded structures are most effectively detected by the through-transmission mode of ultrasonic inspection.