Due to the high transparency of glass materials, it is technologically demanding to use laser processing to generate high-contrast lettering or markings on glass products. However, there is a steadily growing market demand in fields like product traceability, counterfeit protection, or decorative features. In order to obtain precise high resolution marks, pulsed deep UV excimer lasers are applied. The short wavelength (193 nm, 248 nm) is strongly absorbed by most glasses, which facilitates the material removal and offers the advantage of high resolution.
Diffractive marking: A laser interference pattern is created on the glass surface by phase mask projection, which then leads to a periodic micro-relief by material removal. When illuminated, such a relief grating causes a brilliant color impression changing with illumination and viewing angle. In the case of pixelated marks like data matrix or QR codes, the mark is fabricated pixel by pixel, where each pixel consists of a diffracting grating structure. The formation of large area marks instead is accomplished by a scanning scheme, where the work piece is moved at constant velocity, so that the travel between successive laser pulses corresponds to an integer multiple of the interference period. In this way, despite processing on the fly, a predefined number of pulses ≥ 1 per position can be applied.
Plasmonic marking: Glass can be colored by introducing gold or silver nanoparticles. The plasmon resonance of these nanoparticles leads to specific absorption bands. Irradiation with a pulsed UV laser can be used for the implantation of metal nanoparticles from outside into a near-surface region of the glass. Choosing suitable irradiation patterns, spatially selective particle implantation is accomplished leading to colored marks. Due to the incorporation of the particles in the glass, these features are durable and scratch resistant.