A mirror will not work. At the power levels involved, any mirrors must be precisely tuned to the exact wavelength of the laser (e.g. dielectric mirrors) and they must be immaculately clean. That level of cleanliness is impractical in a military environment. Furthermore, the US has developed "white" laser weapons, which will defeat any tuned dielectric mirror like it wasn't there since the lasers have a broad spectrum of wavelengths.
There are fundamental limits to material physics. Spinning doesn't help because there are always fixed points by definition. There are both materials science and engineering limits to spin rates, so you can precisely design your laser power levels to be reliably effective at the upper bound spin rates. All of this was fully modeled out and calculated half a century ago. Other countermeasures, like dielectric mirrors, would be very expensive to use on cheap weapons, and the US already developed a counter-countermeasure anyway with the invention of lasers that emit "white" light.
The scientists and engineers that did R&D on this over the last several decades weren't idiots. Everything "obvious" that armchair weapons experts might come up with were accounted for a long time ago.
That alone would be a major capability for a layered defense system. Cleaning up decoys would be another one (not necessarily getting those down, IDing them due to reflectivity is almost as good).
1. Russia had its own DEW system since at least 2018, and doesn’t currently use it on or off the battlefield
2. Israel has Iron Beam, reportedly a 100KW DEW system, and also doesn’t use it
Perhaps it’s not as cool as it says on the tin?
A common misconception