Something very similar happens in a laser cooling apparatus, except such devices start with a warm cloud of atoms moving in numerous directions at variable velocity. Starting with a laser frequency well below the resonant frequency, photons from any one laser pass right through the majority of atoms. However, atoms moving rapidly towards a particular laser catch the photons for that laser, slowing those atoms down until they become transparent again. (Atoms rapidly moving away from that laser are transparent to that laser's photons—but they are rapidly moving towards the laser directly opposite it). This utilization of a specific velocity to induce absorption is also seen in Mössbauer spectroscopy.