Quantum Well Cascade Lasers

Jerome Faist, Federico Capasso, Carlo Sirtori, Deborah L. Sivco, and Alfred Y. Cho, Quantum Cascade Lasers Federico Capasso, Carlo Sirtori, D. L. Sivco, and A. Y. Cho, Nonlinear Optics in Coupled-Quantum- Well Quasi-Molecules... 

The quantum cascade laser is very different from the conventional semiconductor laser that has been described in this article, and is based on the intersubband transitions between the excited states of coupled quantum wells, or superlattice structures, and on the resonant tunneling between the wells as the pumping mechanism. This means that lasing action takes place between energy levels within the conduction band (not between the conduction and valance bands). More importantly, since the electron is still in the conduction band, novel bandgap engineering can provide for a transport mechanism that allows for this electron to be reinjected into another set of coupled quantum wells, and is therefore reused. As a result, one injected... 

Figure 4.19 Principle of multiple quantum-well structure of a quantum cascade laser (QCL). Top right standard QCL device Alpes Lasers)-, bottom right QCL integrated into common laser unit, including drive electronics and TE cooling (Cascade Technologies)...

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