It’s probably CGI? So logically speaking there is no saber prop. To have a physical door melt next to the actor would require some interesting chemical choices. Maybe it’s a miniature they blue screened into the shot in post?
I was thinking the latter; that they melted a prop and then added Liam Neeson in later or just the melting element was added to the shot with Neeson and the door. The way some of the shots are framed though it would make sense that Neeson was added in later. The spark is definitely added in post as the light bouncing off Neeson is way too weak and looks fake (provided you slow down the clip that is).
It could of course be CG, but if so it’s very advanced for the late 90’s. It’s possible they did melt something for real and then used it for reference when animating it.