The photolitic converter
A photolitic converter was a device invented by Naroq, a Deputy Investigator for Kesat Security, to illuminate veridium isotopes.
In 2376, Naroq lent the USS Voyager crew his photolitic converter, for their investigation into a Ba'Neth attack on the Delta Flyer. When it was determined that it could be used to penetrate the cloaking fields of the secretive Ba'Neth, the crew was able to tie the converter into the main deflector, allowing them to illuminate Ba'Neth ships and space stations. In return for information on a weapon that caused neurological damage to Tuvok, Naroq gave the photolitic converter to the Ba'Neth so that they could adjust their cloaking technology to compensate for it. (VOY: "Riddles")
The script described this device as "a high-tech alien apparatus – something like a projector mounted on a tripod."
According to the Star Trek Encyclopedia, 4th ed., vol. 2, p. 140, the photolithic converter was a "sensor imaging device that operates by causing veridium isotopes to scintillate."