Weld the Lock

A cousin trope to Shoot Out the Lock: In speculative fiction, when you want the door to close and stay that way for a while, you weld it shut with a convenient laser.

Film

 * Aliens is more or less the canonical film example. "Whatever you're gonna do, do it fast!"
 * In Star Trek Nemesis, Picard seals the door to the shuttlebay, but discovers that that door is the only way out.
 * In Star Wars: A New Hope, Luke shoots the control panel lock in order to keep the Stormtroopers from getting in. It turns out that the panel also controls the bridge. His makeshift lock doesn't hold for too long, either.
 * Star Trek IV the Voyage Home did it earlier than Nemesis above; Kirk uses a phaser to melt the lock on a door he locked some 20th-century medstaff in. The staff inside are a little surprised at the rather blatant breaking of the Prime Directive, even by the standards of a captain well known for playing fast and loose with said directive.
 * Treasure Planet, Captain Amelia welds the lock on a hatch in order to keep out the rampaging pirates.

Live Action TV

 * In an episode of Firefly, Saffron uses some sort of heating strip thing to weld shut the door to the cockpit.
 * Babylon 5. Garibaldi and the Mars Resistance blow the lock on an Earthforce outpost (depressurising it to immobilise those inside) then weld it shut again. They might have just been repairing the damage however, because someone walks through the door later on.
 * Stargate SG-1 did this with the Stargate iris on a few occasions. The first time it was done to the Beta gate after it had been stolen and used to steal from friendly worlds. The second was to their own gate to prevent any dial ins completely while they tried to extract Teal'c from the buffer.

Tabletop RPG

 * The D20 Modern role-playing system has rules for doing this with thermite.

Video Games

 * When you and a few survivors first barricade yourselves in the Security Room in Dead Rising, Otis welds the entrance door shut. Oddly, when, the door becomes un-welded (not destroyed) with no explanation.
 * During your breakout from the Empirical in Star Wars: The Force Unleashed, a cutscene shows a purge trooper welding shut a door through which you have to go. You also have to go through the purge trooper and two EVO troopers.
 * In recent times, this has been abandoned in favor of cutting the wires, but let it be known that welding an airlock shut was in Space Station 13 first.
 * You can do this in Alien Swarm to close or open doors.
 * You do this in Killing Floor. You can also unweld previously welded doors if you the specimens start attacking you from a different angle, forcing you to escape through the door you were just trying to make impassable.
 * "I told you, I am WELDING this DOAH!"

Western Animation

 * The pilot of Teen Titans shows Starfire welding the door shut to keep out Mammoth. It doesn't hold long.
 * Alexander Luthor welds the vault door to slow down the Crime Syndicate in the direct to DVD Justice League Crisis On Two Earths.