Investigation of Spatial Distribution Properties of Mid-Infrared Quantum Cascade Lasers at 7 µm
The spatial distribution properties of quantum cascade lasers with emission wavelengths around 7 µm were measured. In addition, the emission profile on a plane orthogonal to the propagation axis of the beam were measured and the full width at half maximum (FWHM) on the orthogonal and lateral directions calculated. Both the monomode and multimode structures at different emission powers were tested, showing that the dispersion does not change significantly (in the range between 42° and 52° on the orthogonal direction and between 28° and 32° on the lateral direction). However, the multimode structure presents several local maxima, which makes it difficult to achieve an efficient collimation of the emitted optical power. The results can be used to design a dedicated optical system to collimate and focus the emission from quantum cascade lasers for spectroscopic applications.