Laser action of dye-injected papers by laser pumping

Ever since the first laser in 1960 scientists have been fascinated to explore what is the simplest laser that requires no precise preparation of the lasing medium, no cavity, no optical coating and alignment, and others. This type of laser is now realized by the use of a piece of conventional paper treated with a dye solution, followed directly by the moderate power optical pumping. During the study of the emitting characteristics of a laser dye infused or injected in a small restricted region containing highly scattering sub-micron-particle as well as on various thin randomized texture-like materials like papers and cigarette filters, our repeatable findings demonstrated the lasing action can occur in such simplified paper systems. We confirmed the well-defined lasing thresholds together with spectral narrowing features even though this "paper laser" use no external cavity, special coating and adjustment. It could be suggested that the paper containing the active dye will act as a heterogeneous and continuously disordered system to cause strongly multiple light scattering, so that such dispersive feedback can trap pump photons as well as emitted photons even in a small spatial region to exceed the gain over the loss.