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Interview Annick Bay

How did you get involved with fireflies? Prof. Jean-Pol Vigneron of the UniversitĂŠ de Namur was studying biophotonics, such as iridescent or structural color in beetles and butterflies. He often travelled to Panama to collect samples. He was relaxing one evening while the sun was setting, and fireflies were popping up making a beautiful light show. He realized that the fireflies must face the same challenges of light extraction as we do. When light is produced in a material that has a higher optical density than air, light gets trapped in the emitting material due to total internal reflection. He collected some fireflies and brought them to the lab. I started studying physics because I was passionate about understanding how the

Annick Bay

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world around me works. Although physics provided answers, it also raised questions. I wanted to study something that was more tangible, and where I could see the impact right away. I was in my last year of my Master’s degree, looking for a thesis topic, and asked Prof. Vigneron whether I could work with him. Studying fireflies attracted me and I saw the potential for applying the research to improving the efficiency of LEDs. What did you discover about fireflies? I had been working on structural color in beetles that involved specific structures at sizes of 400 to 700 nanometers, comparable to the wavelength of light. When I looked at fireflies under a scanning electron microscope, I found intriguing structures of the expected size. However, when I modelled the structures, they only slightly improved light extraction. I took a step back, had a closer look at the exoskeleton of the firefly abdomen, and found something that I did not expect: scale-like structures with a periodicity of ten micrometers that protruded about three micrometers. Although the structures were ten times larger than I had predicted, it turns out that they significantly increased light extraction (Bay, Cloetens, Suhonen, & Vigneron, 2013).

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