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Band diagram of two periods of the QCL active region, together with the moduli squared of the wave functions, under an applied electric field of . Lower grey areas represent two adjacent injector minibands. Upper and lower states of the laser transition, labeled 2 and 1, respectively, are displayed in bold. Also highlighted is the ground state of the injector miniband, . Starting from the injection barrier, the layer sequence in nanometers is (from right to left): . layers are shown in bold, and the and thick quantum wells are doped at a level of .
Voltage and emitted power as a function of current density at different heat sink temperatures, for a long, wide active region. The laser was driven in pulsed mode, with a repetition rate and a 0.5% duty cycle. The back facet of the laser was coated with gold. Inset: as a function of temperature in pulsed (solid points) and continuous wave (hollow points) operation.
Emitted power as a function of current density for the same device as shown in Fig. 2, but operated . Ripples are due to atmospheric water absorption. Inset: Spectra at different current densities. To highlight the effect of water absorption, the top panel was measured with the optical path unpurged.
The (a) voltage and (b) differential resistivity plotted as a function of current density at for the laser (solid line) and a mesa (dotted line). Vertical lines correspond to anticrossing between states 2 and .
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