Extremely temperature-insensitive continuous-wave broadband quantum cascade lasers

Abstract

Quantum cascade (QC) lasers are promising light sources for many chemical sensing applications in the mid-infrared spectral range. For industrial applications, broadband wavelength tuning of external-cavity QC lasers with very broad gain-width has been demonstrated. QC lasers based on anti-crossed dual-upper-state (DAU) designs are one of the promising candidates because of its broad bandwidth as well as high device performances. In fact, wide wavelength tuning of external cavity QC lasers with the anti-crossed DAU designs has been exhibited in several wavelengths: the tuning range of ~25% in pulsed mode and <17% in cw mode at room temperature. Here we report conspicuous temperature performances of continuous wave quantum cascade lasers with broad gain bandwidths. The lasers with the anti-crossed DAU designs, characterized by strong super-linear current-light output curves, exhibit the extremely high characteristic temperature for threshold current density, T0~750 K above room temperature. In addition, its slope efficiency is growing with increasing temperature (negative T1-value). For the pulsed operation of a short 1 mm length laser, the temperature coefficient reaches the surprisingly high value of 1085 K over 340-380 K temperature range. The distinctive characteristics of the DAU lasers are attributable to the optical absorption quenching which has been clarified to take place in indirect pumped QC lasers. Such high characteristic temperatures of the DAU-QC lasers provide great advantages for practical applications, in addition to its potential of broadband tuning.