Continuous-wave operation of a 5.2 μm quantum-cascade laser up to 210 K

Continuous-wave operation of a 5.2 μm-type I quantum-cascade laser with more than 5 mW of output power is reported at a heat sink temperature of 210 K (−63 °C). This temperature is within the range obtainable with thermal-electric coolers. The device was mounted epi-side down on a copper submount and exhibited a thermal resistance of ∼10 K/W at 210 K. Using the experimentally determined values for $T_0\text{=136\hspace{0.05em}}\mathrm{K},$ $J_0\text{=535\hspace{0.05em}}{\mathrm{A/cm}}^{\mathrm{2}}$ and $V_{\mathrm{op}}\text{=8.1\hspace{0.05em}}\mathrm{V}$ and the above thermal resistance, the maximum theoretical operating temperature was found to be 212 K, in close agreement with experiment. Thermal simulations show that by improving the device design and heat sinking, thermal resistance can be reduced to 8.8 K/W and the maximum cw operating temperature can be increased to 230 K.