We experimentally study a broadband implementation
of the atomic frequency comb (AFC) rephasing protocol
with a cryogenically cooled Pr3+:Y2SiO5 crystal. To allow for storage of broadband pulses, we explore a novel
regime where the input photonic bandwidth closely
matches the inhomogeneous broadening of the material (∼ 5 GHz), thereby significantly exceeding the hyperfine ground and excited state splitting (∼ 10MHz).
Through an investigation of different AFC preparation
parameters, we measure a maximum efficiency of 10%
after a rephasing time of 12.5 ns. With a suboptimal
AFC, we witness up to 12 rephased temporal modes.