The terahertz frequency region of the electromagnetic spectrum sits at the interface of electronics and optics, lying between the microwave and infrared (IR) spectral regions. Although there are significant challenges to access, understand and exploit this distinctive region of the spectrum, there are immense benefits in its exploration for both discovery- and challenge-led research, from fundamental studies of laser operation through to the development of new spectroscopy instrumentation. The last 25 years has wi…