Absorption depth
PET absorbs 9.3 µm radiation strongly, so the energy stays at the surface and creates a shallow, frosted mark. At 10.6 µm the beam penetrates deeper, melting more material for the same visible result.
Lightweight bottles
As bottle walls get thinner, a deep mark becomes a weak point that can leak under carbonation pressure. A 9.3 µm laser keeps the mark shallow.
Where to code
The shoulder, just below the neck, has the thickest wall and is the usual position. Avoid areas that stretch thinnest during blowing.
Setting up
Use the lowest power that gives a readable code, keep the lens clean with an air knife, and inspect bottles under pressure during trials.
