Article Abstracts | April 2007
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Short-Wavelength Quantum-Cascade Lasers
Recent progress with quantum-cascade lasers makes them attractive sources in the important 3- to 5-μm spectral range.
by Dr. Quankui Yang, Christian Manz, Dr. Wolfgang Bronner, Dr. Klaus Köhler and Joachim Wagner, Fraunhofer Institute for Applied Solid State Physics
There exists a gap in the performance of semiconductor lasers in the 3- to 5-μm-wavelength range, a spectral range of particular interest for molecular spectroscopy as well as for applications such as directed infrared countermeasures. The 3- to 5-μm range is important not only because the characteristic absorption bands of, e.g., CO, N
2O, HCl and CH
2O, lie within this range, but also because there is an atmospheric transparent window in this range.
Because semiconductor lasers are compact and robust compared with other lasers, they are a favored candidate to address the 3- to 5-μm range. There are two approaches to fabricating semiconductor lasers operating at these wavelengths. The conventional method is based on two types of carriers — electrons and holes — making light-generating recombination across the semiconductor’s bandgap (an
interband transition). Semiconductor lasers using this concept are called bipolar or diode lasers because both electrons and holes are involved in the lasing transition...
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