Go with a blu-ray 405nm-- looks weak BUT burns FAST.. smallest dot of all that we use.
I call them the 'most dangerous' of lasers and 'for sure' one that the kiddos should NEVER touch.
AFAIK they have the 'tightest' beam of all.
Contact P-man and see if he can sell you a nice one that he made.
You could employ a telescopic beam reducer on a 532nm laser or change out the GRIN/collimator lens pair, basically a beam expander set after the crystal where the beam exits very tight but diverges too fast to make a great far field spot, but it's really not bad, take one apart some time you should be impressed.
The BDR-209 405nm diode is the best direct diode you will find for a tight single mode beam. It is a tiny diode, though. Measuring 3.8 mm, so I would get one pressed into a copper module if you don't have the proper tools to press it yourself. Make sure you limit the current to 550 mA, otherwise it could fail. Good luck.
Do you mean "ablate"? Because a small initial diameter is not how you increase power density at the focal point. Quite the contrary, actually. Furthermore, handheld lasers lack the power to ablate metals reliably. Of all the other etching/carving tools available to you, why have you cast them all aside?