Pneumatically Tunable Droplet Microlaser

An ideally flexible laser may function in unison with minute fluctuations in nature. Lasers made solely from liquids are promising toward this end, but they are intrinsically unstable and have been inapplicable to steady operation under ambient conditions unless they are enclosed in a tailored container or a matrix to prevent the evaporation of the liquid. Here, a simple methodology is reported to form a self‐standing spherical microlaser that is composed fully of liquid and operates steadily even under atmosphere. The robustness and spherical morphology of the droplets are achieved by using ionic liquid as the liquid medium and gently casting the droplets on a substrate covered with hydrophobic nanoparticles to enhance the metastability of the contact angle. The resulting droplets are highly robust and work as efficient long‐lasting laser oscillators. The lasing wavelength is sensitively shifted when the droplets are subjected to a faint breeze or moisture, which is associated with the deformation of the droplet. The morphological and optical responses of the droplet under gas convection are consistently supported by aerodynamic and electromagnetic simulations. The droplets are readily scalable with an inkjet printer without the need for any further treatments.