This paper formally shows that an exponentially rising current is optimal in terms of resistive ohmic loss for driving a semiconductor laser into the gain-switching mode. A metric to quantify the quality of laser operation that measures the similarity of a generated optical pulse to the delta function is proposed. Several circuit implementations to approximate exponentially rising current are developed, including using a driver circuit with BJT output stage, a network of RLC circuits, and a saturating inductor. An experimental comparison between a state-of-the-art sinewave resonant driver circuit and a directly driven laser is performed that favors the latest variant of the driver.