Without more information (do you have a reference?) it is hard to say.
However, AFAIK traditionally THZ radiation has been difficult to generate. Thus there is one rather crude strategy where you just hit a system hard and/or fast (e.g. with a fs laser pulse), and rely on a nonlinear process in it to generate at least *some* THz radiation, which you can then isolate and use (since even with low generation efficiency, some THz is better than none). There are, of course, more sophisticated strategies.