[tired&retired]

This sounds as though it is using the terahertz technology used in spy cameras. They function in the gap between microwave and infrared.

[NorthMountain]

Zheng-Ping and co use an infrared laser with a wavelength of 1550 nanometers

Souhnds like it's using a solid-state laser in the short-wave infrared, in the "gap" between visible and thermal radiation.