Let us consider a thermal engine receiving energy from a radiation and releasing energy towards a reservoir ; and focus in the input part.

In most textbooks dealing with thermodynamics of radiations, the energy conveyed by a radiation is treated as pure heat transferred to the system. 

1. Considering the radiation as a black body radiation, is there a way to understand why the radiation conveys heat, but no work ? Could it be because the entropy flow saturates the energy flow ?
2. Considering the radiative pressure, I would tend to believe work can be provided by the radiation, with a piston like system. Why is this never taken into account ?
3. If the radiation is not a thermal radiation, but a coherent laser light, is the situation any different ?