I remember seeing a simple demonstrator some years back of a laser pulsing against the backside of a spinning disc, the geometry of things causing the heat from the laser to provide thrust.

I can't find the video I saw, but here's a general link on the topic:

https://en.wikipedia.org/wiki/Laser_propulsion#Laser_energiz...

This comes with many problems, but it does bypass the rocket equation, while not requiring Project Orion levels of trouble.

I mean you still need to carry propellant: the stuff that is ablated away. It's just that the exhaust velocity is much higher.

Air from the atmosphere may be the propellant [1]. If sufficient velocity can be achieved before leaving the atmosphere, then no propellant is needed to be carried up on the way to orbit.

[1] https://www.youtube.com/watch?v=XhUasBcoj-Q

The problem is that the super-dense energy of a nuclear blast also evaporates solids and rains gamma rays on everything around.

Imagine how hard space exploration would be if the only practical rocket were a Project Orion.

Nuclear would be better, but it's not quite as good as it seems. Nuclear engines are rather heavier than chemical.