Versatile spectrally shapeable multi-mode terahertz system

We present a multimode continuous wave terahertz spectrometer driven by a compact laser diode with a tunable spectrum. An external feedback based on two optical gratings into the diode allows us to shape the laser emission spectrum, and hence the temporal shape of the terahertz signals. In particular, we show a power enhancement of a factor of ten for individual regions of the spectrum to gain a signal-to-noise ratio in the frequency range of interest.