[Florin_Andrei]

The idea of a spontaneous laser sounds surprising, but perhaps it shouldn't be. Some laser media have so much gain per distance, you get lasing without any optics - just pump energy into the system and it starts flashing.

Nitrogen lasers are like that. If you have a high voltage power supply, you could make a nitrogen laser in an afternoon, and no optics are required at all. Bonus: not even a container is required, since it can lase at room temperature and pressure, even when mixed with oxygen.

[wiml]

IIRC, both Mars and Venus have enough of a natural population inversion in their upper atmospheres for laser action to take place (NIR CO2 lasers). Googling this hits paywalls pretty quickly but it seems to have been investigated in the 1980s.