Laser excitation of Phonon Modes

Can a laser only excite optical modes? The name appears to have historical significance in terms of the sodium ion, but I presume it must be true when looking at the dispersion relationship (the dispersion for light would only cross the optical modes).

The overall context of the question is: when exciting with a laser, is energy eventually dumped into all phonon modes?

• One has to take care that assumptions, models, and approximations are understood. Here I'll assume that in the bulk of an ideal crystal, electronic excitations and phonons are independent. (Truth is that there is mixing, but the excitations of the mixed states are independent.) But this assumption does not hold at a surface. (an edge, for graphene). When light interacts near the surface, there is a transient re-arranging of electrons, and this re-arrangement "drags" ions along, exciting acoustic modes. There's no need to conserve $k$ vector. The surface provides "infinite momentum". – garyp May 30 '14 at 20:55