A ruby laser uses chromium ions in ruby as its amplifying medium. Maiman's report identifies a metastable state fed by optical excitation and red emission near .[ref]
Stimulated Optical Radiation in Ruby by Theodore Harold Maiman. Stimulated Optical Radiation in Ruby, opening and level-scheme paragraphs
The pump stores excitation in the medium; stimulated emission transfers it into the optical field. The simplified three-level laser rate equation explains why the stored population and the output pulse evolve together. New to topics? Read the docs here!