As I understand it defenses depend greatly on pulse duration. Rotation dramatically increases effective armor thickness if energy is delivered over a long time

As I understand it defenses depend greatly on pulse duration. Rotation dramatically increases effective armor thickness if energy is delivered over a long time frame etc. But drop to the nanosecond range and a cloud of plasma which used to be the armor is going to between the laser and what’s left of the armor. That said, you don’t need to drill through a target, a jet of ablated material means an equal and opposite force is going in the other direction. Really though the biggest limitation of a laser defense system is pure kinetic kill weapons. Big thing moving Mach 2+ is deadly even without pinpoint accuracy or being filled with high explosives.