Yttrium Iron Garnet (YIG) is a material with extremely wide ranging applications, having the narrowest ferromagnetic resonance linewidth of any known material. Despite decades of experiments on this material, data relating to its full magnon spectrum is sparse. The spectrum is known to contain 20 branches, but the most thorough work to date relies upon a 3-parameter hamiltonian derived from fitting just 3 (the only 3 that were observed in what is still the only neutron spectroscopic measurement on this material). Increasing interest in YIG for applications in magnonics (the magnon equivalent of electronics) necessitates a direct measurement of the optical magnon modes. Following RB1520403 we have sourced larger, purer crystals and we propose to continue the work we have started and produce the definitive data set on this material along with the most thorough analysis possible.