Like you, in the "caption"y thing at the top, I see gain above 1 THz (1012 GHz) However, in the first paragraph, I see one terahertz (10^12 GHz) Of course,

Like you, in the "caption"y thing at the top, I see gain above 1 THz (1012 GHz) However, in the first paragraph, I see one terahertz (10^12 GHz) Of course, one terahertz should be 10^12 Hz. So perhaps the author of the phys.org article got very confused.