Once the stabilizer gas containing the Pym particles enters the lasing chamber, I use a coupled RF plasma to excite the whole thing. Since it's not hitting the necessary energies, nothing splits into elementary particles--the gas dissociates, but who cares; that's background noise--and instead you get a beam, which can be projected at the target. Aperture and pulse duration determine how large a dose is delivered, and a polarity reversal would result in a growth effect, but this is a prototype and I didn't bother to add those circuits.

[Simple, no? Val folds her arms, waiting for whatever Calvin's next doubtless-scintillating contribution will be.]