Multi-colour QCLs

Here we hope to create an active region, which can support gain at two different frequencies at the same time. Of course, the term multi-colour is slightly misleading as neither of the frequencies will be visible as they are in the THz region of the spectrum.

The active region is incorporated into a single waveguide, supporting modes around both frequencies.

In this diagram the grey block represents the substrate on which the active region is grown. The dark and light green represent the active regions operating at different frequencies, the green arrows represents the THz light emitted from the laser.