Tailoring the emission of terahertz quantum cascade lasers

For THz quantum cascade lasers to prove useful for applications, certain requirements for their spectral performance will have to be met. Here, we focus on the provision of single mode operation. Distributed feedback devices lasing on a single longitudinal mode are reported using both first and second order gratings. We also report the operation of terahertz master oscillator power amplifier structures with the potential to increase the output power which is available in a single mode.