This is similar to an early proposal on the Skylon and other systems. Generally works much better in dense air, and it makes an interesting beam weapon when you aren't launching things with it. I read an earlier proposal which I can now not find which used the same sort of laser aggregation that the NIF was planning on using for fusion containment but as a field of smallish (10kW) lasers which could all be trained on the same target to input a bunch of heat which the target would use to convert a liquid gas into the necessary reaction mass to lift into orbit.

They all seem to peter out at 25 km or so. The goal with lasers was to pick a wavelength that the atmosphere was relatively transparent too but could be easily converted into heat through absorption on the receiving end. Microwaves would work to if you are careful about your wavelengths and don't point them at satellites.