We have demonstrated for the first time that soap bubbles can be used as lasers. Soap bubbles are simple, yet very unique and marvelous objects. They are very interesting to the wide audience, from children of all ages, to researchers of a number of disciplines including mathematics, physics, chemistry and biology. To realize the soap bubble lasers, we doped the bubbles with a fluorescent dye and pumped them with an external laser. The generated light circulated in the wall of the bubble, which consequently worked as a laser cavity. Instead of soap, we also made bubbles from surfactant-like molecules without any water present. Specifically, smectic liquid crystals, which molecules form well defined molecular layers, were used for this purpose. Such bubbles had a completely uniform thickness with an integer number of molecular layers and most importantly they were extremely stable. The bubbles were attached to a tube or free floating in a container filled with carbon dioxide. The resulting whispering gallery mode lasing was observed in the spectrum of the emitted light as hundreds of regularly spaced sharp peaks. Shifts in the lasing wavelengths enabled the measurement of subtle size changes as small as 10 nm in a millimeter-sized bubble. This incredible precision allowed the bubbles to be used as one of the best pressure and electric field sensors developed till now. This unique physical system may in future allow the study of novel optical and mechanical phenomena in thin films.Video: https://youtu.be/oMXFM70Bmh4 
https://indico.ijs.si/event/2342/