  We report on the lattice and spin dynamics in the monopnictide CrAs using
polarized Raman scattering. This system exhibits a first-order
magneto-structural phase transition at T_N~ 265 K, below which the magnetic
moments of Cr form an incommensurate double helical magnetic structure while
the unit cell volume abruptly expands. Across the transition, the frequencies
of the fully symmetric Ag phonons strongly renormalize, which along with the
results of first-principle calculations suggest the presence of a sizeable
coupling of the phonons to the magnetic degrees of freedom in this compound. In
addition, we observe two broad modes around 350 and 1700 cm-1 in the magnetic
phase, which we associate with two-magnon Raman scattering. This work provides
one of the few examples of magnetic Raman scattering from a non-collinear
magnet.
