Along with his fiancee, Garland, a nurse with the United States Army Air Forces, he was assigned to the team investigating the three aliens, whom the military feared were part of an alien invasion force. In that capacity, Jeff initiated the attempts to communicate with the Ferengi, a task which was impossible until Rom was able to repair their universal translators.
Later, when General Denning ordered the Ferengi interrogated, Jeff and Garland were assigned to assist Captain Wainwright in his attempts to extract information from them. When it became clear, however, that Wainwright was willing to exact physical harm to the Ferengi, they incapacitated him and helped the Ferengi escape.
They subsequently took them to Hangar 18, where their ship was being stored, allowing them to leave and return to their own time by recreating the time warp which transported them back in time in the first place. (DS9: "Little Green Men")
Jeff was played by Conor O'Farrell. His last name comes from the script.
According to the novel The Rise and Fall of Khan Noonien Singh, Volume One, he and Faith were married as planned after the events of "Little Green Men". He was subsequently employed at Area 51. In 1986, Project F (as Carlson's operation was known) had a burst of activity after Naval Intelligence gave them several devices, namely a 23rd century Klingon disruptor and communicator, recovered from an intruder named Pavel Chekov who had been captured aboard the aircraft carrier USS Enterprise while it was docked at Alameda Naval Base. However, before more than a cursory inspection could be carried out, the disruptor and communicator were recovered by Roberta Lincoln.
In the subsequent novel The Rise and Fall of Khan Noonien Singh, Volume Two, it is mentioned that Faith had died prior to 1996, making him a widower. His wine of choice was Chateau Picard.
Carlson also appears in the novel From History's Shadow.