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arXiv:2507.18027 · Carbon

Nitrogen-vacancy centre formation via local femto-second laser annealing of diamond

Davin Yue Ming Peng, Alexander J. Healey, Rebecca Griffin, Benjamin P. Cumming, Hiroshi Abe, Takeshi Ohshima, Alastair D. Stacey, Brant C. Gibson, Brett C. Johnson, Philipp Reineck

Published Sep 30, 2025• 4 citations
arXivHTMLPDF

Abstract

Emerging quantum technologies based on the nitrogen-vacancy (NV) centre in diamond require carefully engineered material with controlled defect density, optimised NV formation processes, and minimal crystal strain. The choice of NV generation technique plays a crucial role in determining the quality and performance of these centres. In this work, we investigate NV centre formation in nitrogen-doped diamond using femtosecond (fs) laser processing. We systematically examine the effect of laser pulse energy on NV production and quality using photoluminescence and optically detected magnetic resonance measurements. We also probe the role of pre-existing lattice defects formed by electron irradiation and consider defect evolution over extended dwell times. Finally, we are able to identify a regime where the main action of the fs-laser is to diffuse rather than create vacancies. This local annealing capability expands the toolkit for tailored NV production and presents opportunities for fine tuning defect populations.

DOI
10.1016/j.carbon.2025.120892

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Emerging quantum technologies based on the nitrogen-vacancy (NV) centre in diamond require carefully engineered material with controlled defect density, optimised NV formation processes, and minimal crystal strain. The choice of NV generation technique plays a crucial role in determining the quality and performance of these centres. In this work, we investigate NV centre formation in nitrogen-doped diamond using femtosecond (fs) laser processing. We systematically examine the effect of laser pulse energy on NV production and quality using photoluminescence and optically detected magnetic resonance measurements. We also probe the role of pre-existing lattice defects formed by electron irradiation and consider defect evolution over extended dwell times. Finally, we are able to identify a regime where the main action of the fs-laser is to diffuse rather than create vacancies. This local annealing capability expands the toolkit for tailored NV production and presents opportunities for fine tuning defect populations.
High-density nitrogen-vacancy (NV) centers exceeding 1016/cm3 inside a diamond can be achieved by femtosecond laser irradiation. The number of pulses and pulse energy were adjusted considering the increasing trend of the NV concentration and damage generation. The NV concentration first grew as the number of laser pulses was increased, and then the concentration was temporarily saturated or decreased. By increasing the number of laser pulses more than 2.5–5 × 107, the concentration increased again. The Hahn-echo measurement revealed that electron spins of the substitutional nitrogen center (P1) were dominant source for decoherence and the number of paramagnetic defects induced by the laser irradiation was not significant for degradation of spin coherence of the laser-induced NV centers even without a post-annealing process. Such high-dense ensemble NV centers are crucial for a high-sensitive quantum sensor.
Colour centre defects in diamond are promising candidates for many quantum technologies because they act as isolated two level systems in the solid-state that can be controlled and read-out through photonics [1][2][3]. Realisation of these technologies requires the placement of many highly coherent centres in a regular array with high positional accuracy and high fabrication yield [4]. Previous fabrication techniques have lacked the ability to produce high yields with high positional accuracy without causing irreparable damage to the lattice which reduced the quality of the spin and optical properties [5]. Ultra-fast laser writing has been shown to produce highly coherent nitrogen vacancy (NV) colour centres within the diamond lattice with positional accuracies of order hundreds of nanometers and a stochastic yield. In this case, the yield and positional accuracy is held back by the need to thermally anneal the diamond within a furnace to convert laser generated defects into colour centres; a fabrication step in which there is little to no control over individual site [6]. In this thesis, the ultra-fast pulsed laser writing technique is broached in detail from both a theoretical and experimental standpoint. The theory behind the highly non-linear light-matter interactions is studied and a hypothesis is developed for the energy transfer between photo-excited carriers and the lattice via the non-radiative recombination of self-trapped multi-excitonic states [7]. In addition, this thesis presents an expansion on the laser writing of colour centres through broaching the generation of different colour centres that have some preferential properties over the NV [8], and the development of a new engineering technique involving a local laser anneal [9]. The yield of generated centres is increased from stochastic to deterministic by replacing the global thermal anneal with the local laser anneal in combination with a fluorescence feedback mechanism. In addition, the use of the laser to locally anneal generated centres leads to a factor of five improvement in the positional accuracy due to the highly non-linear interaction of the laser with the material. These results culminate in a key step forward in the development of a large scale quantum device and improved understanding of the highly dynamical processes that occur upon femtosecond laser interaction with a wide bandgap material.
Abstract Diamond hosts a wide variety of colour centres that have demonstrated outstanding optical and spin properties. Among them, the nitrogen-vacancy (NV) centre is by far the most investigated owing to its superior characteristics, which promise the development of highly sophisticated quantum devices, in particular for sensing applications. Nevertheless, harnessing the potential of these centres mainly relies on the availability of high quality and purity diamond single crystals that need to be specially designed and engineered for this purpose. Plasma assisted chemical vapour deposition (CVD) has become a key enabling technology in this field of research. Nitrogen can indeed be directly doped in situ into a high crystalline quality diamond matrix in a controlled way, allowing the production of single isolated centres or ensembles that can potentially be integrated into a device. In this paper we will provide an overview of the requirements for synthesizing ‘quantum-grade’ diamond films using CVD. These include the reduction of impurities and surrounding spins that limit coherence times, the control of NV density in a wide range of concentrations as well as their spatial localization within the diamond. Enhancing the charge state and preferential orientation of the colour centres is also discussed. These improvements in material fabrication have contributed to positioning diamond as one of the most promising solid-state quantum systems and the first industrial applications in sensing are just starting to emerge.
Abstract The nitrogen-vacancy (NV) center in diamond is a promising quantum system for magnetometry applications exhibiting optical readout of minute energy shifts in its spin sub-levels. Key material requirements for NV ensembles are a high NV − concentration, a long spin coherence time and a stable charge state. However, these are interdependent and can be difficult to optimize during diamond growth and subsequent NV creation. In this work, we systematically investigate the NV center formation and properties in bulk chemical vapor deposition (CVD) diamond. The nitrogen flow during growth is varied by over four orders of magnitude, resulting in a broad range of single substitutional nitrogen concentrations of 0.2–20 parts per million. For a fixed nitrogen concentration, we optimize electron-irradiation fluences with two different accelerated electron energies, and we study defect formation via optical characterizations. We discuss a general approach to determine the optimal irradiation conditions, for which an enhanced NV concentration and an optimum of NV charge states can both be satisfied. We achieve spin–spin coherence times T 2 ranging from 45.5 to 549 μ s for CVD diamonds containing 168 to 1 parts per billion NV − centers, respectively. This study shows a pathway to engineer properties of NV-doped CVD diamonds for improved sensitivity.
Nitrogen-vacancy (NV) centers in diamond are expected to be quantum sensing devices such as magnetic and electric fields, temperature, pressure and so on. The generation of NV centers by irradiations of femtosecond laser pulses has been reported. Femtosecond laser can write NV centers in diamond directly and this direct writing can realize a flexible spatial arrangement of NV centers. As the application of the laser system, we have constructed the femtosecond laser irradiation platform for creating the quantum sensing device, such as NV centers. The femtosecond laser pulse is focused on a sample surface by an objective lens and laser pulse intensity is controlled by attenuators. By use of this irradiation apparatus, we have irradiated diamond samples to create NV centers. We could confirm several graphitization spots, but the signal intensity from NV center did not exist. To use the irradiation platform for creating NV centers in diamond, it needs some improvement, more increasing the repetition rate of irradiation laser and/or impurity nitrogen density in diamond sample.
Abstract Nitrogen-vacancy (NV) defect centers in diamond are key to applications in quantum sensing and quantum computing. They create localized electronic states in the diamond lattice with distinct population relaxation pathways following photoexcitation that ultimately enable its unique properties. The defect is known to exist in two charge states: neutral and negative, with respectively one and two known optically-active electronic transitions. Here, we report on the observation of a large number of hitherto undiscovered excited electronic states in both charge states as evidenced by distinct optical transitions in the infrared to ultraviolet part of the spectrum. These transitions are observed by monitoring the electronic relaxation of NV centers after photoexcitation using transient absorption spectroscopy, directly probing transient phenomena occurring on timescales from femtoseconds to microseconds. We also for the first time probed the electron transfer dynamics from the 3 E state of NV− to nearby single-substitutional nitrogen defects (N s ) that leads to the well-known effect of NV photoluminescence quenching.