Continuous-wave operation of a broadly tunable thermoelectrically cooled external cavity quantum-cascade laser

Continuous-wave operation of an external cavity quantum-cascade laser on a thermoelectric cooler is reported. The active region of the gain element was based on a bound-to-continuum design emitting near $5.15\mu \mathrm{m}$. The external cavity setup was arranged in a Littrow configuration. The front facet of the gain chip was antireflection coated. The laser could be tuned over more than $170{\mathrm{cm}}^{-1}$ from $4.94\text{to}5.4\mu \mathrm{m}$ and was single mode over more than $140{\mathrm{cm}}^{-1}$. The output power was in excess of $10\mathrm{mW}$ over $\sim 100{\mathrm{cm}}^{-1}$ and in excess of $5\mathrm{mW}$ over $\sim 130{\mathrm{cm}}^{-1}$ at $-30°\mathrm{C}$.