Comments below this answer suggests that a laser ablation-based propulsion system, where the laser is separate from the object to be accelerated, could accelerate an object to about 1/1000 of the speed of light, and that the electric field would accelerate ablated atoms to nearly the speed of light and therefore generate substantial momentum transfer.

While it's a hypothetical situation, I'm just curious about this acceleration. I normally think of laser ablation as a thermal process; absorbed light dramatically increases the temperature locally in a very thin layer of strongly absorbing material which then expands due to a large increase in temperature. So it would be somewhat analogous to a rocket in that it's thermal expansion that creates the velocity and therefore momentum, though it's a lot hotter than what you can get from combustion of the reaction mass alone.

But is there really a mechanism where the electric field of the laser beam itself can generate enough acceleration to bring the plasma particles to a velocity remotely close to that of light? The light is "AC" at several times 10^14 Hz, how could it provide such a net "DC" acceleration?

Or could it be some kind of self-bias of the plasma due to the short pulse length? Highly mobile electrons escape first, leaving a lot of self-repulsive positive charge that accelerates itself?

Are there sources about the physics behind this kind of proposed propulsion where I can read further?

  • $\begingroup$ Does the laser actually need to accelerate the gas electromagnetically, or just heat it to an extremely high temperature (possibly with secondary heating of the plasma exhaust separate from the initial vaporization)? $\endgroup$ – ikrase Mar 25 '20 at 9:38
  • $\begingroup$ @ikrase My question asks about a specific explanation as described in the first sentence. For your question about laser-thermal acceleration I think you can choose a temperature, calculate the characteristic velocity associated with that temperature, plug it in to the rocket equation, and see what you get for a mass ratio when the final velocity is 0.001 c. $\endgroup$ – uhoh Mar 25 '20 at 9:46

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