The excited energy states of the nitrogen nucleus.
This beautiful optics table took two years to build. It exists in the physics department basement. Quite a few different colours (or energies) of laser light are required to cool a molecule due to the more complex energy level structures (compared with an atom) - resulting in this lovely spectacle. The molecules are cooled to temperatures colder than outer space of less than a mK by hitting them with carefully tuned photons of light that exactly match the quantum energy levels of the molecule taking into account the doppler effect.
Visiting the London Science festival at UCL in early October, I met Gleb Lukicov who had created this beautiful experience for visitors - using a cheap hand held spectrascope they could see the spectral lines emitted by different gases. Each lamp contains a different element (cadmium, mercury, sodium.....) which produces its own unique spectral lines, like a fingerprint. The lines tell us about the atomic structure. Gleb is a young physicist and passionate science communicator.