Since their first demonstration in 1994 quantum cascade lasers (QCLs) represent a permanently growing field of research. Now in 2007 these devices are already available commercially. In contrast to conventional laser diodes QCLs are unipolar devices which rely on light emission caused by intraband transitions of electrons. The subband states and therefore the emission wavelength of the device can be engineered within a wide range by varying the thickness of layers in a semiconductor heterostructure. Fields of application are the generation of light in the mid- and far-infrared domain, the later one also known as the terahertz region (THz). This corresponds to wavelengths of several m to several 100 m.
Nonlinear effects, such as second harmonic generation (SHG) allow to access a wider range of wavelengths. These effects are an interesting way to study nonlinear behavior in materials. This work summarizes an approach to improve the efficiency of SHG in gallium-arsenide/aluminium-galliumarsenide (GaAs/AlxGa1-xAs) based QCLs by the use of phase-match gratings, etched in the waveguide. Grating periods from 22 m to 30 m were realized and characterized. Although no clear relation between grating period and nonlinear behavior could be found, conversion efficiencies of up to 46.1 W/W2 have been measured.