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Phase effects due to previous pulses in time-resolved Faraday rotation measurements

Time-resolved Faraday rotation measurements have proved transformative in the investigation of spin dynamics in semiconductors. In materials with spin lifetimes which are on the order of, or greater than, the laser repetition time, the collective effect of spin polarization due to the whole pump pulse train becomes important. Here, we discuss a relative phase shift which results from these spins. We derive and experimentally validate a closed-form expression which describes this phase shift, and characterize it throughout parameter space. A spin lifetime measurement based on this phase shift is described, and we discuss situations in which the model used must be augmented to be applicable