Question turned out to be off-topic. "Migrated" to Worldbuilding.
I'm referring to two events that I recall immediately (the destruction of the Borg planet in the Scorpion episode of Star Trek: Voyager; and the destruction of Alderaan in Star Wars), but there are dozens of similar examples, if not hundreds, in the entire SF&F canon.
What events are actually meant to happen when a high-energy laser beam hits a planet’s surface that lead to the destruction of the entire planet?
Some of my (maybe very lunatic) possibilities and theories (to verify):
The laser beam penetrates the surface, reaches the core, raises its temperature to boiling or even melting point, and pressure in the surrounding area causes the entire planet to explode.
The laser beam hits only the surface or not-so-deep areas beneath it, but due to surface’s stability being destroyed, this is enough to cause the explosion of entire planet.
The laser beam doesn't even hit the surfaces, but causes changes to the atmosphere starting some kind of destructive process.
Is there any, verifiable by our present knowledge (geology, physics, chemistry), common means of explanation that can be adapted to each or most of examples of such events? Or must each of these examples and situations be treated separately (and each book, story or scenario author does it by its own -- i.e. brings its own theory or explanation)?
EDIT, to clarify: I really believe, this is a pure science-fiction question. I'm referring to exactly these two examples I given (destruction of Borg planet in Star Trek and destruction of Alderaan in Star Wars). And this question is tagged with proper tags. This question somehow turned into be too wide or even general, but the key facts remains. Few days ago I watched VOY: Scorpion again and become really interested, how a fairly small armada of nine (?) bio-ships, can destroy entire planet with a just single blast of laser beam? Star Wars example is an addition, but in the very same mood -- in my humble opinion, even that big Death Star shouldn't have (by a very wide and general means) a firepower enough to blast entire planet hell (since Death Star itself is smaller than an average moon, if I'm not mistaken, and for sure much smaller than Alderaan).