  The nature of dark matter is one of the longest-standing puzzles in science.
Axions or axion-like particles are a key possibility, and arise in mechanisms
to solve the strong CP problem but also in low-energy limits of string theory.
Extensive experimental and observational efforts are actively looking for
`axionic' imprints. Independently on their nature, their abundance, and on
their contribution to the dark matter problem, axions form dense clouds around
spinning black holes, grown by superradiant mechanisms. It was recently
suggested that once couplings to photons are considered, an exponential
(quantum) stimulated emission of photons ensues at large enough axion number.
Here we solve numerically the classical problem in different setups. We show
that laser-like emission from clouds exists at the classical level, and we
provide the first quantitative description of the problem.
