Laser Ultrasound for NDT: investigation of the generation beam shape

Usually laser ultrasonic systems use an infrared laser operating at 10 µm to generate the ultrasound in CFRP objects. However this system suffer from an important drawback: optical fiber cannot be used to transport the high energy beam from the laser output to the target which limits the flexibility of the system to investigated complex shaped objects. To overcome this issue, visible light can be used to generate ultrasound. In our case we use a fiber-coupled laser operating at 532 nm. The output end of the optical fiber is placed on an industrial robot arm. The investigated object remains stationary while the optical fiber mounted on the robot arm scan the object. This system offers large flexibility but laser generation at 532 nm is known to be less efficient than CO 2 system emitting at 10 µm. Increasing the visible pulse power is one of the options but optics and CRFF object will be damaged before the same echo level as CO2 generation can be obtained. An alternative solution consists in the investigation of the generation beam size and shape. We recently developed an optical design composed of an axicon lens able to generate annular beam. The diameter of the beam can be adapted. If the axicon lens is removed the optical system provides a disk whose diameter can also be adapted onto the investigated object. Ray-traycing simulations performed with ASAP and experimental beam profile investigated with a beam profiler show good agreement between theoretical and experimental optical design. An experimental comparison between ring and disk shapes will be presented. The comparisons take into account the beam diameter and the beam intensity but also the effect of the angle of incidence will be presented.TECCOM

Continuous Solar Simulator for Concentrator Photovoltaic Systems

A continuous solar simulator for measuring performance of concentrator photovoltaic (CPV) systems is presented. The illumination system is based on a Xenon lamp, a homogenizer rod, shaping optics and a 30cm diameter collimator. The design optimises the reproduction of the characteristics of direct solar illumination: 32’ divergence, high spatial homogeneity, sun-like spectral distribution, with a maximum intensity of 250W/m². It accommodates pass-band and attenuation filters to tune the beam output. It operates in continuous mode, allowing to investigate CPV thermal aspects as well. The present paper addresses the concept design of the solar simulator and associated performance results

Modeling the potential distribution of the threatened Grey-necked Picathartes Picathartes oreas across its entire range

Understanding the distribution and extent of suitable habitats is critical for the conservation of endangered and endemic taxa. Such knowledge is limited for many Central African species, including the rare and globally threatened Grey-necked Picathartes Picathartes oreas, one of only two species in the family Picathartidae endemic to the forests of Central Africa. Despite growing concerns about land-use change resulting in fragmentation and loss of forest cover in the region, neither the extent of suitable habitat nor the potential species’ distribution is well known. We combine 339 (new and historical) occurrence records of Grey-necked Picathartes with environmental variables to model the potential global distribution. We used a Maximum Entropy modelling approach that accounted for sampling bias. Our model suggests that Grey-necked Picathartes distribution is strongly associated with steeper slopes and high levels of forest cover, while bioclimatic, vegetation health, and habitat condition variables were all excluded from the final model. We predicted 17,327 km2 of suitable habitat for the species, of which only 2,490 km2 (14.4%) are within protected areas where conservation designations are strictly enforced. These findings show a smaller global distribution of predicted suitable habitat forthe Grey-necked Picathartes than previously thought. This work provides evidence to inform a revision of the International Union for Conservation of Nature (IUCN) Red List status, and may warrant upgrading the status of the species from “Near Threatened” to “Vulnerable”

Status of the SALTO demonstrator: project overview and first on-sky operations

SALT

Laser ultrasound flexible system for non-contact inspection of medium size and complex shaped composite structures made of carbon fiber reinforced polymer

We present the development of a contactless laser ultrasound system for nondestructive inspection of CFRP complex structures. Ultrasound are generated by a thermoelastic effect resulting from a green pulsed laser insulating a point of the inspected part. The resulting displacement of the surface point is probed by a two-wave mixing based interferometer working in the near infrared. The system is flexible and completely fiber-coupled. It is able to provide C-scans on complex shaped CFRP aeronautical structures.TECCOM

Digital Holographic Interferometry in the Long-Wave Infrared Range for Measuring Large Deformations of Space Components under Thermal-Vacuum Testing

Holographic interferometry at around 10 µm wavelengths has many advantages. It offers the possibility of large deformation measurement, while being much less sensitive to external perturbations. We present the state-of-the art of this technique applied to several industrial cases of the space industry. In particular, we demonstrate that the technique is well adapted to measurement of full-field deformation maps of space structures undergoing large temperature variations typical to what they experience in space conditions

Afocal combinations and focus control for laser launch telescopes

In the field of ground-based telescopes, laser guide stars (LGS) are artificial stars formed in the sky to serve as a reference for the adaptive optics. The artificial star should have a small lateral extent as this is an important factor for how well the adaptive optics can compensate for atmospheric turbulence. The laser launch telescope (LLT) is a key component of the LGS facility. It uses an afocal system to increase the waist of the laser, therefore reducing the beam divergence and limiting the size of the star. We describe the design process of LLTs and show how a combination of two afocals with controlled defocus can be used to optimize the LGS. First, the impact of defocusing a single afocal and tuning the position of the input beam waist is presented. We then demonstrate how an intermediary afocal system can be used to vary the properties of the beam at the input of the second afocal. With such a configuration, a controlled defocus of both afocals can be performed to tune the artificial star size. Moreover, the two focals configuration can be used to adapt the system to the amount of atmospheric perturbations affecting the beam during the upward propagation.SALT

Ultrasons par laser pour l'inspection de matériaux composites. Comparaison entre génération à 532 nm et 10,6 µm. Effet de la géométrie du faisceau de génération

Un système de contrôle non destructif basé sur la génération d'ultrasons par laser à 532 nm et de détection par laser, entièrement fibré et robotisé, est développé au CSL. Nous le comparons à un système équivalent du CTA basé sur la génération plus classique avec un laser CO2 (10,6 µm). De plus nous montrons les résultats d'investigations concernant différentes géométrie du faisceau de génération.TECCOM

Laser Ultrasound Flexible System using Mid-Wave Infrared Generation Laser for Non-Contact Inspection of Composite Structures made of CFRP

editorial reviewedUltrasonic testing (UT) is commonly used in the industry for the investigation of carbon fiber reinforced polymer (CFRP). It is wide-spread and very efficient but, major problems arise when the shape of the element to be investigated is complex (peak, valley, small radius of curvature...). To overcome these problems laser ultrasonic testing (LUT) can be used and the recent developments show promising results. Compared to classical UT, LUT offers the advantage that no contact nor couplant are needed and points difficult to access can be illuminated by laser beams at distance. LUT usually combines two principles: the first one is the generation of an ultrasonic wave by a laser. For generation, CO2 lasers emitting at 10 μm wavelength are usually used. However, the optical fibers for 10 μm wavelength are not capable to cope with laser ultrasonic system needs. Therefore, infrared systems use a jointed articulated beam delivery system which limits the flexibility of the arm. To circumvent this limitation, an all-fibered laser ultrasonic system can be used. For this purpose, visible wavelengths are becoming more common. However, visible generation is more likely to damage the sample under investigation. Halfway between these two technologies, OPO lasers are commercially available in the range of 3 to 3.5 μm wavelength. They already have been considered in earlier experiments with CFRP which show that it is an advantageous wavelength compared to visible/near infrared or far infrared generation. Mid-infrared (MIR) generation is expected to combine both advantages of visible and far-infrared. Solutions now exist for transporting MIR light of OPO lasers into fiber, thus avoiding articulated beam delivery system. Also MIR can be used at higher power than visible light without damaging the surface of the sample under investigation. For these reasons, we have started developing a fully-fiber coupled laser ultrasonics head with MIR OPO generation to put on a robot arm for the non-destructive inspection of CFRP components. In this conference, we will present the first step of this development, and results obtained on a reference plate with the OPO and are compared to those obtained with the green (532 nm) and far infrared (10.6 μm) generations.LDCOM