HIGH-POWER CONTINUOUS-WAVE QUANTUM CASCADE LASERS

High-power continuous-wave (CW) laser action is reported for a quantum cascade structure operating in the midinfrared (lambda similar or equ al to 5 mu m). Gain optimization and reduced heating effects have been achieved by employing a modulation-doped funnel injector with a three -well vertical-transition active region and by adopting InP as the wav eguide cladding material to improve thermal dissipation and lateral co nductance, A CW optical power as high as 0.7 W per facet has been obta ined at 20 K with a slope efficiency of 582 mW/A, which corresponds to a value of the differential quantum efficiency eta(d) = 4.78 much lar ger than unity, proving that each electron injected above threshold co ntributes to the optical field a number of photons equal to the number of periods in the structure, The lasers have been operated CW up to 1 10 K and more than 200 mW per facet have still been measured at liquid nitrogen temperature, The high overall performance of the lasers is a lso attested by the large ''wall plug'' efficiency, which, for the bes t device, has been computed to be more than 8.5% at 20 K, The spectral analysis has shown finally that the emission is single-mode for some devices up to more than 300 mW at low temperature.