Main Question or Discussion Point
Here's a weird idea: solid materials each have an inherent, but potentially modifiable mechanical resonance frequency. Step 1- energize the material mechanically by inducing vibration (ie. increasing the amplitude of occillations). Step 2- strike the material intermittently with an intense and pulsed electromagnetic waves (EM frequencies corresponding to bond energies within the material so that it can induce mechanical movement), pulsed "in phase" at the mechanical resonance frequency of the material inducing propulsion.