True story: many years agio, the groupI was in was doing research on Laser Propulsion for space flight. This wasn’t light pressure, but a system suggested by Arthur Kantrowitz in which you ablated a thin layer of a propellant block with a powerful laser pulse, then pumped energy into it, causing it to expand. In essence, you keep the rocket motor on the ground and only have to send up reaction mass with your payload (Yes, this was ground-to-orbit launching).
We needed something to put into the reaction mass to make it ionize easily. Alkali metal compounds looked good, because it’s easy to pop off the extra electron. We looked through the list of compounds and found…
In crystal form.
We put it in, and it didn’t work worth a damn. Butm, as far as I know, we’re the only people who ever tried to use real Dilithium Crystals for spacecraft Propulsion.