The technical challenges for Breakthrough Starshot list the huge amount of power required for accelerating a solar sail to interstellar travel speeds and the precise targeting of laser beams of that energy as difficulies.
On the other side, laser emission from deep space are not unheard of
astronomer Donald Menzel who first observed and classified this particular planetary nebula in the 1920s (it is officially known as Menzel 3 after him) was also one of the first to suggest that in certain conditions natural ‘light amplification by stimulated emission of radiation’ – from which the acronym ‘laser’ derives – could occur in nebulae in space. This was well before the discovery of lasers in laboratories.
Being able to detect the laser emissions as such great distances (8000 ly) will require immense level of power at source (immense by the measure of what humans can control today), so lasing will happen accross large optical paths in an actually very rarefied nebula gas (roughly one light year across with particle densities of 100 to 10,000 particles per cm3)
Closer to home, however, we have - kinda readily available - higher gas densities in higher percentage of excitation/ionization.
Can one use the Earth's aurorae as a lasing medium? (IR and VIS)
How about Jupiter's? (UV)
could Sun's corona act as an acceptable lasing medium? If positive, in what wavelengths?
is there any other medium inside the Solar system that may exist in "pumped enough state" to support lasing?
if one can use any of the above as lasing media, what are the challenges of approaching the things from this angle for a solar sail propulsion of the Breakthrough Starshot kind? Examples (but please feel free to list any other challenges one may plausibly think):
- precise focusing may be a problem, but only if one cannot generate enough power for the focusing to not be an issue, at least on the acceleration leg inside the Solar system
- radiation wavelength may impose some special approaches be taken in the construction of the solar sail.
- if a non-Earth setup is necessary, one will likely need to place the starting point of the solar sail closer to the body used for lasing. What challenges would this create?
Note: this is "science-based" - speculations are encouraged as long as they are plausibly based on scientifically known facts (of course, the answers are not required to pass the review process for publication in a science journal).