High-performance quantum cascade laser sources for by Wittmann, Andreas

By Wittmann, Andreas

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5 µm, based on the three-quantum-well design in the InGaAs/AlInAs/InP material system, using low-pressure MOVPE. 8 µm/h (which is comparable to that of an MBE system) while the growth rate was increased to 3 µm/h for the waveguide layers [91]. The laser performance is comparable to that of similar MBE grown structures. 5. Continuous wave operation above room temperature For many applications, high spectral resolution (in the MHz range) is an absolute necessity. Therefore, the devices must be operated in CW operation in order to avoid thermal chirp (shifting of the emission wavelength by thermal heating of the device during the pulse).

In order to calculate the lineshape of the multi-optical transition power spectrum Lspon (E) , each optical transition with its specific Lorenzian lineshape, has to be weighted by the oscillator strength and the cubic energy: Lspon (E) ! 45) j As will be shown later, the correct linewidth for different active region designs could be calculated [102]. 29) has a different lineshape for multi-optical transitons: ( ) Lgain (E) ! 46) For the active region designs considered here, one can neglect the lower state population (strong inversion) and the gain spectrum can be extrapolated from the spontaneous emission power spectrum: Lgain (E) !

Lasers using such a design worked up to a temperature of 320 K [60]. , also at Bell Labs, used a completely different concept for achieving gain by using a superlattice (SL) active region rather than establishing gain between discrete energy levels. In this concept, electrons emit photons corresponding to the energy gap (minigap) between two superlattice conduction bands (minibands). A distinctive design feature of this concept is the high oscillator strength of the optical transition at the mini-Brillouin zone boundary of the superlattice.

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