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-, -, and -point conduction band edge energy profiles (thin black lines) of a single cascade calculated with an electric field of . The moduli square of the injector/extractor miniband states and the excited states are depicted using gray lines. Thick solid lines highlight the upper and the lower laser states 2 and 1, and the the injector-miniband state 3, that may contribute to the broadening of the emission spectrum.
Low resolution emission spectra of the QCL driven with pulses ( , ) at (black) and (gray). Full widths at half maximum of the electroluminescence are at and at . High-resolution laser spectrum measured at the same drive conditions at is also shown (not to scale) with a black line for reference.
Applied voltage across the laser structure together with the total peak emission power of the laser as functions of current. The laser is driven with (bias)/ (power) current pulses and the power is corrected for approximately 50% collection efficiency.
Threshold current density, , vs heat sink temperature for a laser driven with current pulses. The solid line is an exponential fit in the temperature range used to determine the characteristic temperature . The inset shows a high resolution Fourier-transform spectrum measured just above the threshold at .
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