ALESSANDROTREDICUCCI,I,2CLAIREGMACHL,IMICHAELC.

At presentefficient,compact,solid-statesourcesfor the spectral range 1-10THz, alsoknownasthe"terahertzgap",are still lacking. Quantumcascade(QC)lasers possess the potential for the efficient generation offar-infrared light, although many important physical questions have to be addressed when the transition energy is reduced below the optical phonon frequency. Significant progress towardsfar-infraredQC laserscanbeobtainedusinginter-minibandtransitionsin semiconductor superlattices and employing non-conventional laser waveguide designs. Surface plasmon modes at the interface between a metal and the semiconductorareexploitedin thedesignofa A- 19 !-lm(15.8 THz) superlattice QC laser, which represents the longest wavelength lIl-V semiconductorlaser to date.Single-modeoperationisachievedatA- 16!-lmwiththeadoptionofadual­ metal Bragg grating which modulates the skin depth of the surface plasmon. Preliminaryelectroluminescenceresultsat- 3.5THzarealsodiscussed.