[thegp]

not a physicist, but an electrical engineer.

At least 2 principles that I know allow a laser to push things:

1) photons do have impulse, given by its energy divides by the speed of light. This causes Radiation pressure (see https://en.wikipedia.org/wiki/Radiation_pressure ) 2) if a laser vaporises part of a structure, the resultant gas will push against the structure, delivering momentum

[FreeFull]

Both principles have an impact, and in this case, I think the second one is the one that causes most of the impulse.