Mid‐infrared lead‐chalcogenide diode lasers can be operated at convenient operation temperatures using short current pulses and thus allow a wide range of potential applications. Our goal was to optimize the spectral characteristics of pulsed lasers by well‐defined current pulse shaping. The high‐frequency current tuning coefficient has been evaluated experimentally for this reason. Different tuning mechanisms are discussed by use of a model calculation. The qualitative features can be explained by assuming a separate temperature for the carriers that form a thermodynamic system of their own and are heated by the current. The tuning characteristics can be explained due to carrier concentration variations induced by free‐carrier absorption. ©1996 American Institute of Physics.