Not quite as simple as that. Terahertz != Short Wave Infrared != Midwave Infrared != Longwave Infrared ("thermal"). These all require different photosensitive elements in your detector. They also have extremely different atmospheric absorptions. [1]
These particular sensors might indeed be passive, but it would limit their range and SNR. Be wary of manufacturers simply selling the emitter as a second SKU to garner the label passive on their detectors.
These particular sensors might indeed be passive, but it would limit their range and SNR. Be wary of manufacturers simply selling the emitter as a second SKU to garner the label passive on their detectors.
[1] I work at a company making SWIR/MWIR imagers.