27 April 2016 Low-threshold external-cavity quantum cascade laser around 7.2 μm
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Room-temperature continuous wave (CW) operation of a tunable external-cavity quantum cascade laser (EC-QCL) at center wavelength around 7.2 μm 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–Pérot 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 μm). 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/cm2 and a high output power of 50 mW were obtained when the EC-QCL was operated in CW mode at 20°C.
© 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
Zhibin Zhao, Zhibin Zhao, Lijun Wang, Lijun Wang, Zhiwei Jia, Zhiwei Jia, Jinchuan Zhang, Jinchuan Zhang, Fengqi Liu, Fengqi Liu, Ning Zhuo, Ning Zhuo, Shenqiang Zhai, Shenqiang Zhai, Junqi Liu, Junqi Liu, Zhanguo Wang, Zhanguo Wang, } "Low-threshold external-cavity quantum cascade laser around 7.2 μm," Optical Engineering 55(4), 046116 (27 April 2016). https://doi.org/10.1117/1.OE.55.4.046116 . Submission:

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