These errors do not at all affect the results and conclusions presented in Ref. 1. In the remainder of this Erratum, we provide a physical interpretation of Eq. (1), which expresses the differential field E in terms of the excited population, the driving field E0, and the Green function G (the response of a charge to an infinitely short acceleration). In Eq. (1), t represents the time at which the differential field E is probed, and t − τ represents the time at which the pump beam (assumed infinitely short) excites the sample. The differential field vanishes whenever the probe precedes the pump (τ < 0). The electric far field produced by a sheet of phased oscillators is proportional to the oscillators’ current. In Eq. (1), the current is calculated as a temporal integral over all velocity contributions Ġ due to infinitely short accelerations (δ kicks) exerted by the driving field E0. For a given value of the integration variable t′, the δ kick occurs at time t − t′, and the driving field exerts a force on the charge proportional to E0(t − t ′). The charge responds to this force with a velocity proportional to Ġ. At time t, which is a time lapse t′ later than the δ kick, the velocity of the charge is proportional to Ġ(t ′). The interpretation of Eq. (1) is more complicated when the excited population decays in time. Figure 1 shows three population profiles as a function of time. For a decaying population (continuous line), the population at time t is a subpopulation of that at time t − t′. Hence, the population of charges giving rise to the differential field at time t is a FIG. 1. (Color online) The three times for Eq. (1). The differential field is evaluated at time t. The charge is accelerated by the driving field at time t − t′. The population is created by the pump pulse at time t − τ . Three population profiles are depicted: an exponentially decaying profile (continuous line), a constant profile (dashed line), and a growing profile (dotted line).