Don't hold your breath waiting for that. The GFP inside the cell is the gain medium, but all the energy is coming from another laser outside the cell. So, while

Don't hold your breath waiting for that. The GFP inside the cell is the gain medium, but all the energy is coming from another laser outside the cell. So, while a self-lasing organic structure is marginally more plausible today than yesterday, the hard part of that problem still remains, and it is much harder, and this paper doesn't even attempt to solve that problem. If a chemist figures out how to generate enough power inside a cell to get a population inversion in a laser's worth of an organic fluorescent protein, it will make this result seem positively boring by comparison, and "powering a cell laser" will be the least of the applications.