Because of the change in photon energy, it is an inelastic scattering process.

While the inelastic scattering processes and consequently the electronic mean free path depend on the energy, it is relatively independent of the material.

The idea is that whatever physical process one is trying to study may be modeled as a scattering process of these well separated bound states.

During inelastic scattering processes, significant energy exchange happens.

There is significant change in carrier energy during the scattering process.

In an inelastic scattering process, some of the energy of the incident particle is lost or increased.

These particles must not appear as the end-states of a scattering process.

There are rules governing which molecular vibrations/rotations can participate in this scattering process.

It is also possible to observe molecular vibrations by an inelastic scattering process.

Therefore, it is desirable to use laser pulses that are faster than the dominant scattering processes.