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SCIENCE AT WORK Optics Putting the LEDs back in Laser BY EDDY DELCHER Inside the pumping module are the crystal and the LEDs (not visible), cooled by water (red and blue cables). © A. BARBET/LCFIO 1. Laboratoire Charles Fabry (CNRS / Institut d’Optique Graduate School / Université Paris-XI). 2. A. Barbet et al., “Revisiting of LED pumped bulk laser: first demonstration of Nd:YVO4 LED pumped laser,” Optics Letters, 2014. 39(23): 6731-4. Environment A joint research team involving the LCF1 and the specialized company EFFILUX has developed a solid-state laser amplified by light emitting diodes (LEDs), a cheaper and more reliable alternative to laser diodes.2 Solid-state lasers, which use a solid as gain medium (as opposed to gas or liquid in other laser types), are found notably in laser pointers and used for cutting and welding. They conventionally work by flashing light into a crystalline rod to inject energy into it in the form of photons, a process known as “pumping.” As the atoms in the rod soak up these photons, they get into an excited state, releasing the extra energy as a new photon. This new particle travels up and down the rod at the speed of light until it collides with another excited atom, causing it to release not one, but two photons. These continue to bounce up and down until they escape the rod through a tiny aperture, forming a concentrated light beam. Since the 1980s, the pumping at the heart of the system was performed by laser diodes—the ones Assessing Nanopollution BY EDDY DELCHER A team involving researchers from the CIRIMAT,1 the LAAS,2 and the EcoLab3 have devised a new method to assess carbon nanotube (CNT) pollution in the environment.4 Extremely light, strong, and displaying electrical properties, CNTs are nearly ubiquitous in the manufacturing of a large number of products, such as cars, electronic components, and sports equipment. But their increasing prevalence has raised concern that some might be accidentally released in the environment during production or use. While it is possible to assess rejected amounts in small samples and within the confines of a laboratory, accurate readings in nature are far more complicated given the high quantities of carbon already present in the environment. The scientists based their research on amphibian larvae, the animals most affected by water pollution. By measuring their electrical permittivity, that is, the resistance encountered when an electric field passes through a medium, the researchers 10 CNRS INTERNATIONAL MAGAZINE were able to determine the quantity of CNTs present in the samples. “We first measured the permittivity of CNTs alone, and of non-exposed larvae as references. We then checked that of larvae exposed to CNTs and compared it with the previous results. The difference between the two gave us a direct indication of the quantity absorbed,” explains Emmanuel Flahaut, who led the research. “Following exposure, the larvae quickly release the CNTs from their body. Now we have a tool to assess how long it takes to flush them out completely,” concludes Flahaut. This technique could be used to measure the quantity of CNTs in other complex environmental samples, such as contaminated soils or plants. ii flahaut@chimie.ups-tlse.fr 1. Centre inter-universitaire de recherche et d’ingénierie des matériaux (CNRS / Université Toulouse-III / INP Toulouse). 2. Laboratoire d’analyse et d’architecture des systèmes (CNRS). 3. Laboratoire écologie fonctionnelle et environnement (CNRS / Université Toulouse-III / INP-ENSAT). 4. E. Flahaut et al., “Quantitative detection of carbon nanotubes in biological samples by an original method based on microwave permittivity measurements,” Carbon, 2015. 81: 535 –545.


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