Fast Gain Dynamics in Interband Cascade Lasers

Interband Cascade Lasers (ICL) have matured into a versatile technological platform in the mid‐infrared spectral domain. To broaden their applicability even further, ongoing research pursues the emission of ultrashort pulses. The most promising approach is passive mode‐locking with a fast saturable absorber. However, despite vast attempts no passive mode‐locked ICL has been demonstrated up to date. In this study, pump‐probe measurements are conducted on the ICL gain, demonstrating that 60–70% of its dynamic behavior is characterized by a rapid recovery time of 2 ps. The findings explain why passive mode‐locking of ICLs has not succeeded so far, shedding a new light on ICL dynamics as strategies are proposed to overcome the current limitations.