And the ideal spot would be 90° away from the direction it is heading towards us.
The problem; as I see it; is that the laser would be quite near Earth and the jet would be mainly on the lead surface.
The laser is on a spacecraft sent TO the asteroid. The spacecraft holds a “station keeping” position near the asteroid, and wails away on it with its laser. The jet would directed in whatever vector that would optimize deflection.
Seems like whatever power source was on the spacecraft with the laser could be more efficiently used if it were merely a booster to push the rock as needed.