Opt. Lett. 37, 130–132 (2012)

Scientists in France have developed a fibre-based source of 'black light' — a source that emits broadband ultraviolet radiation but only small amounts of visible light and no infrared light. Thibaut Sylvestre and colleagues from the Université de Franche-Comté and Université des Sciences et Technologies de Lille in France say that their black-light source could be useful for performing gas absorption spectroscopy or exciting various fluorescent proteins used in biological studies. The researchers made their source by pumping a specially designed silica photonic crystal fibre with 355 nm light pulses from a Q-switched frequency-tripled Nd:YAG laser. Four-wave mixing and cascaded Raman generation combine in the fibre to provide a broadband continuum output that spans from around 350 nm to 390–480 nm, with the exact spectral width dependent on the pump power. There is a sharp spectral cut-off beyond this point, with emission at longer wavelengths dropping to a negligible level. Solarization in the fibre causes the bandwidth and spectral power density of the continuum to decrease strongly after 20 minutes of operation. The researchers are now attempting to overcome this limitation by using alternative fibres that are more resistant to ultraviolet-induced damage.