Laser marking is a quick and accurate process using the focused laser beam to generate labels or patterns on the material surface. It has unique advantages such as fast and permanent marking with high-resolution and non-contact marking, suiting lasers for metal back marking. Especially, thanks to a pulse width shorter than that of metal electron-to-lattice coupling time (~1-2ps), non-thermal laser and matter interaction does not change chemical properties and makes an anti-corrosion black marking on medical metals possible.

https://www.mddionline.com/manufacturing-processes/studying-anti-corrosion-surface-black-marking-medical-grade-metal-ultrafast