Fig. 1. Schematic conduction band diagram of a portion of the active layers under an applied electronic field of 28 kV/cm. The moduli squared of the relevant wave functions are shown. The layer sequence of one period of the structure in angstroms starting from the injection barrier (toward the right side) is as follows: 41/31/9/59/7/60/8/56/9/51/15/49/21/48/23/43/29/40/30/38/31/35, where In0.52Al0.48As barrier layers are in bold, In0.53Ga0.47As quantum wells are in roman, and the doped layers (Si, 2.3×1017  cm−3) are underlined. The inset shows a schematic of the diagonal transition and nonresonant extraction scheme.

Fig. 2. Lasing spectra of the QCL at various temperatures. The inset is a lateral far-field radiation pattern at the heat sink temperature of 293 K.

Fig. 3. Pulsed PIV characteristics for an HR-coated 4 mm long and 40 μm wide QCL at various heat sink temperatures. The frequency of driving current is 5 kHz, and the duration is 2 μs.

Fig. 4. Threshold current density and slope efficiency at different temperatures, where the dashed curves are theoretical fittings.

Fig. 5. Average output power characteristics of the laser at heat sink temperatures from 293 to 353 K.