Modeling Fs-Laser-Induced NV Centers Generation in Diamond

The nitrogen-vacancy (NV) color center in diamond is under investigation for quantum applications due to its advantageous properties, including photostability, long coherence time, single-photon emission at room temperature, and optically detectable and controllable spin states. Various techniques have been studied for the controlled formation of NV centers, with femtosecond laser micromachining standing out for its micro/nanometric precision in creating microstructures within the surface or volume of materials. Such high precision is due to nonlinear optical absorption, which is confined to the laser focal volume, and minimized thermal effects, as the femtosecond laser pulse duration is shorter than the molecular vibrational period. This method produces vacancies in the lattice, which when near substitutional nitrogen atoms, generate NV centers. Thus, micromachining can accurately produce color centers in specific locations. In this study, fs-laser-induced generation of nitrogen-vacancy centers in CVD diamond was performed at distinct fluences, pulse durations (185 fs – 1 ps), and wavelengths (1030, 515 and 343 nm) to identify the optimal conditions for its creation, with implications for developing novel quantum technologies. The fs-laser processed samples were analyzed by confocal microscopy, with the sample excited at 543 nm to identify the NV^- zero-phonon line emission at 637 nm. From the confocal microscopy images, it was possible to determine the NV center defect area as a percentage of the total area from each fabricated microstructure. Thus, it was possible to analyze the effect of experimental conditions on the concentration of new defects. We observed the generation of NV centers is proportional to the peak laser fluence and inversely proportional to the pulse duration and wavelength. A three-state model based on the diamonds nonlinear excitation was used to interpret the observed results, from which it was possible to determine the effective multi-photon absorption cross-section and the saturation fluence for colors center generation for each excitation wavelength. Therefore, our results shed light on the understanding and controlling of NV centers generation in diamond under fs-laser irradiation.