Terahertz radiation can penetrate many materials, but generating it has been tricky. An old trick turns out to be overlooked, in that a small compressed gas container (pen-sized , with nitrous oxide gas) can generate a tunable laser if (stimulated/pumped) with a tunable infrared laser.
New technologies open up new research opportunities. Opportunity does not really knock at your door, it whispers...."This is an opportunity".
SEE:http://news.mit.edu/2019/tunable-ter...ghing-gas-1114

pete