Broadband quantum cascade laser gain medium based on a “continuum-to-bound” active region design

We present quantum cascade laser designs at $7–9μm$ with two lower injector states strongly coupled with the upper laser state at the operating electric fields. Optical transitions from these three coupled states contribute to a large gain spectrum width (⁠$∼250cm−1$ full width at half maximum), which enables external cavity tuning of the lasers over $200cm−1$⁠. Lasers show comparable performance to the conventional narrow band design at a similar wavelength with a peak modal gain coefficient of $∼10kA/cm$⁠, a slope efficiency $∼1W/A$⁠, and good temperature performance $(T0=170K)$ in pulsed mode operation at 295 K.