  Inelastic scattering of photons is a promising technique to manipulate
magnons but it suffers from weak intrinsic coupling. We theoretically discuss
an idea to increase optomagnonic coupling in optical whispering gallery mode
cavities, by generalizing previous analysis to include the exchange
interaction. We predict that the optomagnonic coupling constant to surface
magnons in yttrium iron garnet (YIG) spheres with radius $300\,\mathrm{\mu}$m
can be up to $40$ times larger than that to the macrospin Kittel mode. Whereas
this enhancement falls short of the requirements for magnon manipulation in
YIG, nanostructuring and/or materials with larger magneto-optical constants can
bridge this gap.
