May 03, 2020
Recently, the laser micromachining research team of the State Key Laboratory of laser physics, Shanghai Institute of Optics, and precision machinery, the Chinese Academy of Sciences has made progress in the application of ultrafast laser-induced fluorescent anti-counterfeiting of transparent materials. The team uses the ultrafast laser to induce and control the density of light-emitting defects in quartz glass, so as to realize the anti-counterfeiting application of light-emitting defects. Relevant research results were published in Optical Materials Express.
Because of its short pulse width and high peak power, the ultrafast laser can produce a nonlinear effect. It can not only modify the surface of transparent materials such as metal, semiconductor, glass but also adjust the performance of transparent materials. In the early stage, the team has used the ultrafast laser to induce a periodic stripe structure on the surface of non-transparent materials such as metals and semiconductors to realize anti-counterfeiting.
For the internal anti-counterfeiting of transparent materials, this study found that when ultrafast laser interacts with quartz glass, the hydrogen-oxygen bond of hydroxyl will be broken preferentially, resulting in non-bridged oxygen hole center (defect center), which can emit visible red fluorescence under very weak UV irradiation.
By adjusting the pulse width and power of the ultrafast laser, the arbitrary three-dimensional pattern can be written in the high hydroxy quartz glass by ultrafast laser. The pattern is invisible to the naked eye in the sunlight, but it emits red fluorescence under the excitation of ultraviolet light, so as to realize the hidden anti-counterfeiting. In addition, the defect fluorescence center wavelength is located at 650nm, which is suitable for biomedical optical therapy. Therefore, it is expected to promote the red fluorescence produced by the defect center to be used in biomedical detection experiments in the chip laboratory.
Fig. 1 the barcode pattern written by ultrafast laser in high hydroxyl quartz glass is invisible in (a) sunlight and emits red fluorescence under (b) ultraviolet excitation
Fig. 2 (a) based on the schematic diagram of the chip laboratory in the high hydroxy quartz glass, and (b) the red fluorescent defect array of the non-bridged oxygen hole center prepared by ultrafast laser in the high hydroxy quartz glass