The Time Travelers aka’s: Depths Of The Unknown/The Return Of The Time Travelers
A time travel experiment that was supposed to produce a window into time turns out to be a portal instead. One of the experimenters steps through into a not-too-distant-future world that has been destroyed by nuclear war. Some of the others follow, but then the portal phases out and they can't get back. Stars Preston Foster, Philip Carey and Merry Anders. Also with John Hoyt.