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Correlation between noise properties and coherent coupling of lateral modes in quantum cascade lasers

: Kinzer, M.; Yang, Q.K.; Hugger, S.; Schilling, C.; Ostendorf, R.; Aidam, R.; Driad, R.; Bronner, W.; Fuchs, F.; Wagner, J.


IEEE Journal of Selected Topics in Quantum Electronics 19 (2013), No.4, Art. 1200108, 8 pp.
ISSN: 1077-260X
Journal Article
Fraunhofer IAF ()
beam steering; laser mode dynamics; lateral modes; quantum cascade (QC) laser

We report on investigations of far-field intensity patterns and angle-resolved lasing spectra emitted fromquantum cascade (QC) lasers at wavelengths around Lamda = 7.7 µm in pulsed operation. Measurements of the angle-dependent intensity noise in the far-field reveal that small driving currents lead to an incoherent superposition of multiple lateral cavity modes. Elevated currents result in a phase-coupled superposition of the light fields arising from the excited lateral modes. This superposition leads to beam steering and strong pulse-to-pulse intensity fluctuations. We present for both the incoherent and the phase-coupled superposition, a model which allows us to explain the observed far-field intensity patterns and their noise properties. The angle-resolved lasing spectra of the investigated QC lasers show distinct sets of longitudinal modes with distinctively different dependences of the lasing spectrum on the far-field angle. They can be assigned to the incoherent and the phase-coupled superposition of the lateral modes.