External cavity quantum-cascade laser tunable from 8.2to10.4μm using a gain element with a heterogeneous cascade

A heterogeneous quantum-cascade structure based on two bound-to-continuum designs emitting at 9.6 and $8.4\mu \mathrm{m}$ is presented. Its spontaneous emission spectrum at room temperature has a full width at half maximum of $350{\mathrm{cm}}^{-1}$ and shows a variation of intensity of less than 20% over more than $200{\mathrm{cm}}^{-1}$ . External cavity lasers using a grating in Littrow configuration and antireflection coated chips with this active region could be tuned over $265{\mathrm{cm}}^{-1}$ from $8.2\text{to}10.4\mu \mathrm{m}$ , that is, over 24% of the center wavelength.