Toward Simultaneous Coherent Radiation in the Visible and Microwave Bands with Doped Molecular Crystals

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, simultaneous generation of radiation in multiple widely-separated bands presents formidable challenges with a single gain medium. Herein, 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 pentacene doped in p-terphenyl is proposed. 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. This 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.