High performance “continuum-to-continuum” quantum cascade lasers with a broad gain bandwidth of over 400 cm−1

A quantum cascade laser structure is demonstrated that provides a broadband gain spectrum of 430 cm−1 with a peak emission wavelength around 4.8 μm. The laser active region is based on multiple transitions from strongly coupled upper states to lower laser states. In spite of the broad gain spectrum, high laser performance was demonstrated with low threshold current density (as low as 1.6 kA/cm2), large slope efficiency (over 5 W/A) and high wall plug efficiency (up to 23%) in pulsed mode operation at 295 K.