QR code micro-certified gemstones: femtosecond writing and Raman characterization in Diamond, Ruby and Sapphire

This paper reports on a micro-certification procedure using femtosecond laser irradiation to microscopically mark a single-crystalline gemological and natural diamond, synthetic ruby and synthetic sapphire, inscribing a QR Code on them. The QR-code was composed of a set of 25 × 25 micropoints, and the irradiation energy was optimized at 1kHz repetition rate. The code was made at a 20 µm relative depth into the gemstone surfaces by controlling the incident laser energy, that was set to 3 μJ for all the samples. Characterization by optical and electron microscopy, as well as micro-Raman hyperspectral imaging showed that the microdots have a diameter of about 14 µm perpendicular to the irradiation direction, being laterally spaced by 14 µm-18 µm applied for each sample. This work corroborates the feasibility of using ultrafast laser inscription technology to fabricate microdots with great quality on gemstone surfaces, which offers a great potential for the jewelry industry to safely micro-encrypt gemological certifications. The compositional and morphological characterization of the modified surface was carried by micro-Raman spectroscopy and scanning electron microscopy.