  Coherent sources exploiting the stimulated emission of non-equilibrium
quantum systems, i.e. gain media, have proven indispensable for advancing
fundamental research and engineering. The operating electromagnetic bands of
such coherent sources have been continuously enriched for increasing
demands.Nevertheless, for a single bench top coherent source, simultaneous
generation of radiation in multiple bands, especially when the bands are widely
separated, present formidable challenges with a single gain medium. Here, we
propose a mechanism of simultaneously realizing the stimulated emission of
radiation in the visible and microwave bands, i.e. lasing and masing actions,
at ambient conditions by utilizing photoexcited singlet and triplet states of
the pentacene molecules that are doped in p-terphenyl. The possibility is
validated by the observed amplified spontaneous emission (ASE) at 645 nm with a
narrow linewidth around 1 nm from the pentacene-doped p-terphenyl crystal used
for masing at 1.45 GHz and consolidated by a 20 fold lower threshold of ASE
compared to the reported masing threshold. The overall threshold of the
pentacene-based multiband coherent source can be optimized by appropriate
alignment of the pump-light polarization with the pentacene's transition dipole
moment. Our work not only shows a great promise on immediate realization of
multiband coherent sources but also establishes an intriguing solid-state
platform for fundamental research of quantum optics in multiple frequency
domains.
