Search

Nitrogen-vacancy centers in diamond have gained widespread attention as quantum systems that can be applied in quantum information devices. The excellent properties of quantum devices can be enhanced using preferentially oriented nitrogen-vacancy (NV) centers. However, thus far, orientation control has been achieved only via chemical vapor deposition. In this study, we demonstrate the creation of preferentially oriented NV centers via laser writing. The alignment ratio of ensemble NV centers is biased along the direction parallel to [111], depending on the femtosecond laser polarization, causing an increase of 55 % in contrast to the optically magnetic resonance signal at maximum compared with 25 % in random orientation. Based on time-dependent density-functional theory (TDDFT) simulations and experimental observations, such complex polarization dependence can be attributed to the anisotropy of electron excitation. This technique provides a new optical fabrication method for engineered materials and devices used in quantum technology.

Laser texturing has been proven to be an effective method to improve the tribological behavior of titanium and its alloys, while the hardness of the textured surface is still poor. To further strengthen the surface, a two-step laser processing experiment was conducted on Ti6Al4V alloy including femtosecond laser texturing and in-situ nitriding. Firstly, the sample was textured with femtosecond pulses at laser fluence of 6.37 J/cm2 and a repetition rate of 200 kHz. Then, the textured surface was micro-melted and nitrided by irradiation in a nitrogen atmosphere at a low laser fluence of 0.43 J/cm2 and a high repetition rate of 19 MHz. After nitriding, a uniform crack-free TiN coating was prepared on the top of the as-textured structures with thickness of 40–60 μm, and the surface hardness was significantly improved from 336 HV to 1277 HV. The reinforced phase TiN had microstructures of dendrites in the upper region and particles in the bottom region of the nitrided layer. The morphology analysis revealed that only a slight change in height was introduced to the textured structures by femtosecond laser nitriding and the designed functions could be maintained.