High performance quantum cascade lasers with broadband gain spectra

QC laser active regions with multiple transitions from strongly coupled upper laser states to lower laser states were designed to achieve broad gain spectra as well as high performance. Two broad gain QC laser designs in the 7-9 m wavelength region were demonstrated based on the continuum-to-bound design. The first embodiment of one design at ~8 m enables external cavity tuning over 190 cm-1(7.5 - 8.8 m) in pulsed mode operation at 0°C. We also demonstrated a QC laser structure based on a continuum-to-continuum active region in the 4-5 m wavelength region with a gain spectrum of ~ 430 cm-1. External cavity tuning over 340 cm-1(4.4 - 5.2 m) was achieved with this design in pulsed mode operation at 15°C. In spite of the broad gain spectrum, a low threshold current density (1.6 kA/cm2), large slope efficiency (4.5 W/A), good temperature performance (T0=160 K), high peak power (up to 5 W) and high wall plug efficiency (WPE, up to 20%) were achieved for ridge lasers with as cleaved facets, in pulsed mode operation at 295 K, demonstrating that it is possible to make a wide gain spectrum compatible with high power and efficiency performance.