Dresden 2009 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 35: Semiconductor Laser

HL 35.6: Vortrag

Mittwoch, 25. März 2009, 15:30–15:45, BEY 154

Time-resolved lasing-characteristics of external-cavity quantum-cascade (EC-QC) lasers emitting around 7.4 µm — •Borislav Hinkov, Frank Fuchs, Wolfgang Bronner, Klaus Köhler, and Joachim Wagner — Fraunhofer Institute for Applied Solid State Physics (IAF), Tullastraße 72, D-79108 Freiburg, Germany

Quantum-cascade (QC) lasers are semiconductor light sources covering the infrared spectral range from around 3 µm to 15 µm. For use in e.g. molecular fingerprint absorption spectroscopy the spectral tuning range of QC lasers can be extended significantly using external-cavity (EC) setups.

We investigated the temporal evolution of the lasing spectrum of an EC-QC laser emitting around 7.4 µm on a ns time-scale, applying 100 ns long pulses. Immediately after turn-on of the current pulse multiple-mode lasing starts at the gain maximum of the QC laser controlled by the cavity formed by the chip facets. After a time delay of about 10 ns the QC laser begins to couple to the external cavity as seen from a change in lasing wavelength to that defined by the external grating as wavelength selective element, reaching steady-state operation after 24 ns. The characteristic time constant for the change from internal cavity modes to external cavity operation is derived to 15 ns, comparable to the photon lifetime in the external cavity of 4.5 ns.

The dynamics of this coupling process is not only of fundamental interest but also important for practical applications because most EC-QC lasers are operated in short-pulsed mode.