Datasheet

4.5 Beam Properties
4.5. Beam Properties
Divergence
Figure 4.8 shows a typical ALPES LASERS QCL beam profile. Unipolar lasers consist
in tightly confined waveguides; for this reason, the beam diffracts strongly at the output
facet and has a full divergence angle of about 60 degrees perpendicular to the layer
(vertical angle) and 40 degrees parallel to the layers (horizontal angle). A f/1 optics
will typically collect about 70% of the emitted output power. Note that the collected
output power will decrease with the square of the f-number of the collection optics.
Figure 4.8.: QCL beam profile.
Polarization
Because the intersubband transition exhibits a quantum mechanical selection rule,
the emission from a unipolar laser is always polarized linearly with the electric field
perpendicular to the layers (and the copper submount).
Mode
ALPES LASERS QCLs are designed to have a single spatial mode, typically the Gaus-
sian TEM00 mode. A mode measurement can be performed by ALPES LASERS on
demand for a specific application.
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2012 SA 53