Conductivity artifacts in optical-pump THz-probe measurements of YBa₂Cu₃O₇

Transient changes in the complex conductivity of the high-temperature superconductor YBa₂Cu₃O₇ have been measured with optical-pump THz-probe spectroscopy. Artifacts in the conductivity arise when optical excitation induces changes in the material response that occur on a time scale comparable with or faster than the THz pulse width. A model is presented that agrees with experiments and provides insight in distinguishing between artifacts and real features in transient conductivity measurements.