Disclaimer: I’m not a chemist. I’d be keen to hear a trained chemist’s viewpoint, but this is my understanding of the process:
The “activated” part of activated charcoal (AC) comes from the porous nature of the granules, and typically the AC has additional product added to it to increase it’s absorption of certain materials.
One of the more likely offensive off-gasses you produce from lasing is hydrogen chloride (HCl) gas, which is why it’s important to check the Material Safety Data Sheet (MSDS) before lasing in order to avoid it. Or chlorine gas in general, for that matter.
Fish don’t like chlorine, and they don’t like ammonia. Most AC used for fish tanks have additives mixed in to increase absorption of ammonia and chloramines. Chlorine will easily dissipate as a gas but is much harder to neutralize when bonded with water, because when you mix water with HCl you get hydrochloric acid. Since this is a dry system, let’s just stick to the gas.
Most commercial fish dechlorinators are based on plain sodium thiosulfate (Na2S2O3), a crystalline salt that generally comes pre-mixed with distilled water, usually in a 1% solution. Most fish charcoals coat the AC with this type of solution.
Sodium Thiosulfate basically neutralizes HCl into salt (NaCl) and sodium carbonate (aka washing soda), Na2CO3.
PS.- The Chlorine industry has an informative website at