Ultrafast femtosecond laser micro-marking of single-crystal natural diamond by two-lens focusing system

The inscription of unique logo and security marking on diamonds and gemstones is in high demand by worldwide manufacturers and businesses for anti-counterfeiting purposes and traceability. Short pulsed lasers enable marking of transparent materials, challenge remains to produce digital security micro-features on thin facets of the natural diamond in a non-intrusive manner. We propose the design and demonstration of a novel two-lens focusing system to inscribe diamond at microscale and high throughput by an ultrafast laser scanning process. A threshold laser fluence of similar to 2.5 J/cm(2) and a scan speed of 2 mm/s realized writing of high-contrast data matrix code and serial number without inducing defects and cracking in the diamond. Characterization revealed smooth ablation depth profile with distinct laser-induced periodic surface structures (LIPSS) in the laser inscribed regions determined through scanning electron microscopy (SEM) and 3D optical microscopy. Raman spectroscopy revealed diamond cubic structure dominating with mixing of graphitic structure in the laser markings at various scanning speeds. Comparing with the 0.05 NA f-theta lens, the two-lens focusing system offered 7x improvement in the marking resolution (3 mu m in line-width) in addition to its simplicity and add-on flexibility to industrial laser marking systems.

Automated summary

There is a high demand for unique logos and security markings on diamonds and gemstones for anti-counterfeiting purposes and traceability. This study proposes a novel two-lens focusing system for inscribing diamonds at a microscale with high throughput using ultrafast laser scanning technology, achieving high-contrast data matrix codes and serial numbers without causing defects or cracking. The system offers a 7x improvement in marking resolution compared to traditional lenses, with the added benefits of simplicity and flexibility for industrial laser marking systems.