Rubidium blue fluorescence

In this image, we see the emission of blue light from rubidium atoms in a warm vapour cell. The atoms are iluminated with two lasers, detuned from S-P and P-D transitions on the Rb D2 line (both close to the infared, at 780 and 775 nm). Decay by a different path leads to the fluorescence being a distinvctive blue. The red light is scatter from the lasers.

Image taken at the university of Bath.