Abstract
Lasers generate coherent, collimated, intense and monochromatic radiation at optical wavelengths with precise spatiotemporal control. This unique combination of attractive properties is stimulating the design of optical cavities and gain materials to replicate the functions of lasers at the microscale with the ultimate goal of developing miniaturized light sources for biomedical and information technologies. Borrowing from the fundamental principles of macroscopic dye lasers, microscopic analogs able to sustain light amplification by stimulated emission of radiation from fluorescent dyes have, indeed, become a reality. Microdroplets of dye solutions are their simplest implementation. Large numbers of dye‐doped microdroplets with identical shapes and sizes can be produced efficiently, inexpensively and rapidly to permit the convenient investigation of their properties with statistical confidence. In fact, a solid understanding of the geometrical, optical and photophysical factors regulating the ability of a single dye‐doped microdroplet to produce laser emission has already been developed. As a result of these seminal studies, methods to control the lasing spectrum of a dye‐doped microdroplet with external stimulations are now available, providing access potentially to miniaturized lasers with tunable emission. In particular, mechanically‐, optically‐ and thermally‐induced deformations in the shape of a microdroplet, changes in its size or modifications in the absorption coefficient of its constituent components are all viable strategies to manipulate lasing. The latter mechanisms rely on structural and/or electronic modifications of the dyes in the microdroplet interior to regulate the fine balance between optical gain and absorption losses responsible for lasing and are the primary focus of this review.