Magneto-optical traps use laser-cooling combined with magnetic fields to isolate clouds of neutral atoms. Room temperature atoms fly about at many hundreds of meters per second. To capture them in a single location, lasers interact with the atoms, removing energy through the absorption and emission of photons. The development of laser cooling earned Steven Chu, Claude Cohen-Tannoudji and William D. Phillips the 1997 Nobel Prize in Physics. Rubidium is the most common element used, but the image shown here is of a strontium cloud trapped inside a vacuum chamber.
Strontium has some nice atomic properties making it an up-and-coming star. One feature is that strontium atoms trapped in an optical lattice makes for a stable atomic clock. Strontium has narrow atomic transitions, which are relatively insensitive to electromagnetic surroundings that might disrupt the atomic clock ticking. The "ticks" of today's atomic clocks are based on the energy levels that arise from the interactions of the swirling electrons and nucleus within an atom.