Electrically switchable emission in terahertz quantum cascade lasers.

Electrically switchable emission in a terahertz quantum cascade laser is demonstrated. Two active region designs are incorporated into the same waveguide, forming a heterogeneous cascade that lases at frequencies around 2.6 THz and 3.0 THz. We find that the position of the active regions within the waveguide does not effect the sequence in which the two colours reach laser threshold. The devices show good performance, with 2.6 THz and 3.0 THz modes operating up to 60K and 91K respectively and displaying thresholds as low as 79 Acm(-2) for the 2.6 THz mode.