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Power scaling of quantum cascade lasers via multiemitter beam combining

: Hugger, S.; Aidam, R.; Bronner, W.; Fuchs, F.; Lösch, R.; Yang, Q.K.; Wagner, J.; Romasew, E.; Raab, M.; Tholl, H.D.; Höfer, B.; Matthes, A.L.

Volltext urn:nbn:de:0011-n-1459127 (726 KByte PDF)
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Copyright 2010 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.
Erstellt am: 15.8.2013

Optical engineering 49 (2010), Nr.11, Art. 111111, 5 S.
ISSN: 0091-3286
ISSN: 0036-1860
ISSN: 1560-2303
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IAF ()
quantum cascade laser; power scaling; spectral beam combining; external cavity; microlens array; coupling efficiency

Different approaches to power scaling of 4.5- to 5-µm emitting quantum cascade (QC) lasers by multiemitter beam combining are investigated. Spectral beam combining of linear arrays of QC lasers consisting of several individual emitters located side by side is demonstrated as a first variant, using an external cavity equipped with a diffraction grating and a partially transmitting output mirror providing wavelength-selective feedback to each emitter. In this way, spectral beam combining of up to eight individual QC lasers is achieved with an optical coupling efficiency of 60% for an array of six emitters. The resulting beam quality (M 2 < 2 for both fast and slow axes) is close to that observed for single emitters. As a second approach, a linear array of QC lasers is coupled to a custom-made array of silicon microlenses positioned in front of the output facets of the QC lasers. This technique produces a set of closely spaced parallel output beams, strongly overlapping in the far field, without introducing any coupling losses. The resulting beam divergence is given by the aperture size of the microlenses, which is limited by the center-to-center spacing of the QC lasers (500 µm in our case).