Datasheet

A. QCL theory and application notes
A.1. QCL wavelength range
Unlike standard bipolar semiconductor lasers (e.g. 1.55µm telecom devices), for
which the emission wavelength is closely related to the band gap energy, the QCL
transition consists in the transition of an electron inside sub-bands, from one upper
quantum well level to a lower quantum well level.
A series of potential wells and barriers for the electrons are built by using two dif-
ferent semiconductor materials (InGaAs and AlInAs), These wells and barriers are so
thin that the electrons are allowed only a discrete set of energy levels, similar to the
orbitals of an atom. The positions of the allowed energy levels are determined by
the thicknesses of the wells and barriers, making it possible to define a wide range
of laser transitions by using only one material system (InGaAs/AlInAs grown on InP).
This range is limited by the intrinsic absorption of the material and the potential differ-
ence between the wells and barriers.
All QCLs are grown using the same materials, but with layers of specific thicknesses
and compositions to obtain a given emission wavelength, which is determined by the
geometry of the semiconductor layers that compose the laser crystal.
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