Excited‐State‐Modulated Dual‐Wavelength Single‐Mode Lasing from a Single‐Component Organic Microbelt

Abstract Single‐mode laser is of fundamental importance due to its beam quality and spectral purity. However, common lasers operate in multimode as the dimensions of most laser resonators are much larger than the operating wavelengths. Herein, the novel dual‐wavelength single‐mode lasing from a solution of self‐assembled single‐component microbelt that consists of excited‐state intramolecular proton transfer molecules is demonstrated. The large modulation of the gain regimes and the cooperative effect between gain and loss in the cavity are proven experimentally and theoretically to be effective strategies for achieving multiple‐wavelength and single‐mode operation. These results broaden optical science and provide new insight into the construction of multicolor lasers with high spectral purity for the on‐chip integrated photonic system.