The time dependence of the reflection of the output mirror for a two‐level pulsed laser is determined for an arbitrary time‐dependent pumping rate. The result derived using the methods of optimal control theory is given as an explicit function of time. The optimal reflectivity eliminates relaxation oscillation spikes so that the output is a smooth function of time. Moreover, the peak instantaneous intracavity photon density of the optimal solution is significantly reduced relative to the photon density using constant reflectivity, thereby increasing the fluence without reaching the damage threshold. Numerical examples for a Nd+3/YAG system is provided. A practical feedback mechanism for controlling the output mirror reflectivity as a function of time that well approximates the optimal solution is proposed.