A study of the temporal response of a biased planar nematic liquid crystal to short (∼10 &mgr;s) voltage pulses is presented. The resulting optical phase shift varies quadratically with time during the first 2 &mgr;s after switching the voltage on and then linearly. A theoretical model is developped starting from the Leslie‐Ericksen theory which describes the investigated phase modulation in the microsecond time scale. ©1995 American Institute of Physics.