One of the foundational assumptions of D&D 5e is that things listed in the DMG are the DM's purview. The list of firearms is there, not in the PHB, because the DM gets to decide whether (and which) of those firearms exist or could be created. The artificer class even notes this in it's proficiency.

If your Dungeon Master uses the rules on firearms [...], your artificer is proficient with them.

Emphasis added

You will have to ask your DM whether laser pistols exist or not, and the answer to that is RAW for that campaign.

One of the foundational assumptions of D&D 5e is that things listed in the DMG are the DM's purview. The list of firearms is there, not in the PHB, because the DM gets to decide whether (and which) of those firearms exist or could be created. The artificer class even notes this in it's proficiency.

If your Dungeon Master uses the rules on firearms [...], your artificer is proficient with them.

Emphasis added

You will have to ask your DM whether laser pistols exist or not, the RAW is that only some campaigns have them.