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 $8.4μm$ is presented. Its spontaneous emission spectrum at room temperature has a full width at half maximum of $350cm−1$ and shows a variation of intensity of less than 20% over more than $200cm−1$⁠. External cavity lasers using a grating in Littrow configuration and antireflection coated chips with this active region could be tuned over $265cm−1$ from $8.2to10.4μm$⁠, that is, over 24% of the center wavelength.