Trying to find 60s or 70s sci-fi movie (or tv episode) that ends with laser gun & countdown

Hello, all.

I’m trying to locate a science fiction and/or adventure film, or possibly the conclusion of a series episode. Date of production - I would say made somewhere between 1967-1983, at some point in that 16 year period. Set on earth, not in space.

I saw the conclusion (only) on Saturday or Sunday afternoon television in Southern Indiana somewhere between January 1983-June 1985. It was done in color - and not high end - kind of shoddy color that looked like a B or C-grade movie or a series episode. If I had to guess on the production date, I would say early 70s.

In slo-mo, a group of people races to escape from a high-rise before the building detonates. One of the men in particular has unusually long hair, and the slow-motion shows it flying up on the sides. They are running, running, running, and take an elevator to the ground floor to escape.

Meanwhile, it periodically cuts back to a futuristic laser gun, that rotates upward toward the camera. Every 5 or 6 secs the angle gets closer to 90 degrees. Just as the escapees manage to hit the ground floor and dive out of the building, the laser reaches eye level and the building immolates and explodes.

I’ve gone through everything I can think of to find this, including reviewing the following:

Laserblast (not it - totally different kind of film)
The Bionic Woman (not it, although it has a similar sequence in one episode)
Logan’s Run - the movie (not it)
Buck Rogers in the 25th Century (not it - too polished looking and too campy)
The Six Million Dollar Man (not it)
Mission: Impossible - the series (not it)
Colossus: The Forbin Project (not it)
Z.P.G. (not it)

This is significant for me because it was so beautifully cut together, and as a massive film fan, it’s the first time in my life when I really noticed the semiotics of editing. It may have been low-budget, but whoever filmed this knew what they were doing.

I’m so eager to find this that I’ve been scouring old tv listings from my hometown over a 2 1/2 year period of Jan. '83-Jun. '85. It’s a VERY tedious task and is turning up lots of b-grade sci fi and adventure movies, but is taking eons. If anyone can help me, I would be grateful. Thank you!