Low-threshold external-cavity quantum cascade laser around 7.2 μm

Room-temperature continuous wave (CW) operation of a tunable external-cavity quantum cascade laser (EC-QCL) at center wavelength around 7.2 mu m is presented. The EC-QCL was implemented in a Littrow configuration. The gain chip is based on a diagonal bound-to-continuum design with a high-reflection coating on the back facet. A two-layer antireflection (AR) coating consisting of Al2O3 and ZnSe was designed and deposited on the front facet of the chip to suppress the Fabry-Perot modes. With this AR coating, single-mode tuning range of 128 cm(-1) was achieved, from 1346.7 to 1475.3 cm(-1) (6.78 to 7.43 mu m). High side-mode suppression ratio over 30 dB was achieved near the center gain region. A very low-threshold current density of 0.89 kA/cm(2) and a high output power of 50 mW were obtained when the EC-QCL was operated in CW mode at 20 degrees C. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)