How does a laser heat up a material?

[v_pino]

Can you please provide some explanation for the following two questions? Or please provide some links. Thank you.

1.) How does a laser heat up a material? Does the material absorb a photon and the material's atom gets excited? - when the atom relaxes, it emit an energy equal to that of the photon? Even if this is so, doesn't it only mean that the material remains at the same temperature that it was before? - it absorbs the same amount of energy that it releases.

2.) Why is a laser visible only when it hits a surface?

 

[zhermes]

1) when the material absorbs photons, the energy is absorbed as kinetic energy as well as atomic excitations; thus the material is heated overall.
2) to see something, light has to reflect off of (or be emitted from) it. Most lasers passing through air don't scatter enough light towards your eyes so they are invisible until they hit a surface that more effectively scatters light.