ABSTRACT
In this chapter, the authors summarize recent results on the investigation of second harmonic generation associated with intersubband transitions at λ~10 µm in the AlInAs/GaInAs material system. The lower effective mass of the GaInAs compared to GaAs has the advantage of the larger matrix elements for the same intersubband transition wavelengths. In the geometry the beam from a stabilized CO2 laser, after entering the sample at the normal incidence (on one of the polished edges) and traversing the superlattice, is reflected off the top surface of the mesa and passes a second time through the multilayers. The second harmonic radiation is collected by a lens, followed by a sapphire window to cut the 10 µm radiation, an analyzer and filters to select the second harmonic. The second harmonic power is expected to increase quadratically with the power of the primary beam.
