There are two main types of military lasers: Free Electron Lasers (FEL lasers from now on) and Medium Lasers.
FEL lasers work by "wiggling" electrons through a line of magnets to create coherent photons. More information here. Theoretically, they can create any frequency of light by altering the electron speed.
On the other hand, Medium Lasers work by pumping energy into a medium. Some examples are the common Helium-Neon lasers used in laser pointers, and Carbon Dioxide ones used for laser welding.
FEL lasers require large magnets and electron beams. They are also more expensive because they are more complicated. On the other hand, Medium lasers only need a chunk of the medium, and some energy source. They are cheaper. Because of this, space-based satellite lasers should be most commonly Medium Lasers.
A common shielding technique is to use a Plasma Window. This device utilizes magnetic fields to contain a sheet of plasma, which should block hostile weapons fire.
I had the idea that a Plasma Window could block any type of Medium laser by seeding its plasma membrane with the lasing medium. On the other hand, FEL lasers would be able to create any frequency of light, including light that can't be absorbed or emitted by any compound. Would this be a valid reason why FEL lasers could be preferred over Medium lasers?