Microwave beamed power

Has anybody investigated the use of microwave beamed power as a way of
eliminating the first stage of a rocket?

To put it more precisely to assist a rocket by beaming microwaves to it
and to use these microwaves to heat the air as it goes through a ramjet
like engine. Higher up where there is no air it could heat pure
hydrogen that is expelled from a tank. This would be like a solid core
nuclear rocket engine but would not have any radiation nor shielding
issues.

I am pretty sure that large amounts of microwaves can be cheaply made
with vacuum tubes and beamed up by a ground based power station. I also
know they can be received by antennas and converted to DC power by
diodes, but this would not be the best way in this case. We would have
to heat the hydrogen somehow using the incoming microwaves. Perhaps
some kind of microwave absorbing tubes could be used that can also
stand high temperatures. Like some kind of ceramic coated refractory
metal.

Any thoughts are appreciated.

Z