Astrophysical masers are a well known phenomenon when molecules within a stellar atmosphere get excited and emit coherent photons. When it happens around an (active) galactic nucleus, it’s proportionately brighter hence the aptly-named megamaser.
To be clear, astrophysical masers are different than what LaserSETI is looking for in a number of ways. First, these are radio waves, not visible light. Second, they shine equally in all directions (isotropic) vs. human-made lasers which are a focused beam (spatially coherent). Third, they don’t turn on and off like a light switch.