  Chiral phonons possessing valley pseudo angular momentum (PAM) underlie a
diversity of quantum phenomena of fundamental and applied importance, but are
challenging to probe directly. We show that deficiencies of typical
momentum-resolved electron energy loss measurements that make it impossible to
distinguish the PAM of chiral phonons can be overcome by introducing pinwheel
free electron states with well-defined PAM. Transitions between such states
generate 2D periodic arrays of in-plane field vortices with polarization
textures tailored to selectively couple to desired chiral mode symmetries.
