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Setup of a Confocal Fluorescence Microscope for the Detection and Characterization of Single NV Centers in Diamond

Manuel Riedmann, Lucas Kirchbach, Andreas Stute

Published Feb 5, 2026• 0 citations
OpenAlex

Abstract

Single nitrogen vacancy (NV) centers in diamond serve as a photonic platform for quantum sensing and computing applications. They can be created deterministically using femtosecond laser pulses. Such writing process requires high-resolution fluorescence detection with a high signal-to-noise ratio, which is accomplished by setting up a homebuilt confocal fluorescence microscope. The microscope shall monitor the fluorescence of newly formed NV centers during the writing process. In addition, it will be used to characterize the NV centers’ spin coherence times, orientation in the diamond lattice and single-emitter characteristics via the intensity correlation function g(2)(tau). In the future, this setup is also planned to be employed for STED-microscopy of twin NV centers.

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Optics Express•Nov 24, 2014•16 citations
Single nitrogen vacancy (NV) centers in diamond serve as a photonic platform for quantum sensing and computing applications. They can be created deterministically using femtosecond laser pulses. Such writing process requires high-resolution fluorescence detection with a high signal-to-noise ratio, which is accomplished by setting up a homebuilt confocal fluorescence microscope. The microscope shall monitor the fluorescence of newly formed NV centers during the writing process. In addition, it will be used to characterize the NV centers’ spin coherence times, orientation in the diamond lattice and single-emitter characteristics via the intensity correlation function g(2)(tau). In the future, this setup is also planned to be employed for STED-microscopy of twin NV centers.
Single Nitrogen-Vacancy centers (NV-centers) in diamond can be operated at ambient conditions as qubits in quantum memories and nanoscale quantum sensors. At TH Nürnberg, we plan to deterministically generate single NV-centers via femtosecond-laser pulses and integrate them into photonic platforms via 3D-printed microoptics and fs-written waveguides. This presentation gives a summary about our activites: The design and analysis of micro-lens systems to be manufactured via Two-Photon Polymerization on top of individual, self-written NV-centers for increased photon-collection efficiency, the programming of a spatial light modulator for wavefront optimization, the setup of a confocal scanning fluorescence microscope that addresses individual NV-Centers and laser material processing that allows to shape the diamond surface and to fabricate waveguides in the diamond for efficient optical coupling.
In this work, we present a comprehensive method of characterization and optimization of laser irradiation within a confocal microscope tailored to quantum sensing experiments using nitrogen-vacancy (NV) centers. While confocal microscopy is well-suited for such experiments, precise control and understanding of several optical parameters are essential for reliable single-emitter studies. We investigate the laser beam intensity profile, single-photon emission statistics, fluorescence response under varying polarization and saturation conditions, spectral characteristics, and the temporal profiles of readout and reinitialization pulses. The beam quality is assessed using the beam propagation factor M2, determined via the razorblade technique. An optical fluorescence spectrum is recorded to confirm NV center emission. To confirm single-emitter operation, we measure second-order autocorrelation function g(2)(τ). Saturation behavior is analyzed by varying laser power and recording the corresponding fluorescence, while polarization dependence is studied using a half-wave (λ/2) plate. A temporal laser pulse profile is examined by modulating the power of an acousto-optic modulator. After optimizing all relevant parameters, we demonstrate the microscope’s capabilities in driving spin transitions of a single NV center. This work establishes a straightforward and effective protocol for laser excitation optimization, enhancing the performance and reliability of NV-based quantum sensors.
Abstract Recent advancements in quantum technology have highlighted the potential of nitrogen-vacancy (NV) centers in diamond. However, realizing this potential requires overcoming challenges associated with the size, complexity, and cost of current optical systems. In this Perspective, we present a compact and portable confocal setup designed for efficient detection, initialization, and readout of single NV center photoluminescence signals, enabling coherent spin control and nanoscale-resolution magnetic field sensing.
Abstract Recent advancements in quantum technology have highlighted the potential of nitrogen-vacancy (NV) centers in diamond. However, fully realizing this potential requires addressing challenges related to the size, complexity, and cost of current optical systems used for NV center manipulation. In this work, we present a compact and portable confocal setup specifically designed for the efficient detection and control of single NV centers. Our system facilitates optical initialization and readout of individual NV center photoluminescence signals, enabling coherent spin control and nanoscale-resolution magnetic field sensing.
The nitrogen-vacancy (NV) center is a defect in the structure of diamond, roughly the size of a single atom, that possesses properties that make it applicable to quantum information processing, high-resolution magnetic resonance imaging, and probing biological systems. When an NV center is excited by green light of wavelength 523 nm, it emits red light of in the range from 600-800 nm tens of nanoseconds later. A confocal microscope can be used to excite and collect emitted photons from NV centers. By detecting the intensity of the emitted red photons, we can determine the quantum state of a single NV center, which is needed to build various quantum computing, sensing and imaging devices. The autocorrelation method is used to detect antibunching in the emission of red photons and ascertain that the observed photons are being emitted from a single NV center. We have built an autocorrelation device that measures, with sub-nanosecond accuracy, the statistical distribution of the arrival times of the red photons emitted from a diamond sample at a photon counter. The device can measure fixed time values with a time resolution of 120 ps FWHM. For uncorrelated sources measured for 120 seconds at the TAC full range of 100 ns, the average counts in each histogram bin were about 0.01% of the predicted value. The autocorrelation device that we have built costs about 10 times less than commercial units used by other NV researchers.
Precise positioning of nitrogen-vacancy (NV) centers is crucial for their application in sensing and quantum information. Here we present a new purely optical technique enabling determination of the NV position with nanometer resolution. We use a confocal microscope to determine the position of individual emitters along the optical axis. Using two separate detection channels, it is possible to simultaneously measure reflected light from the diamond surface and fluorescent light from the NV center and statistically evaluate both signals. An accuracy of 2.6 nm for shallow NV centers was achieved and is consistent with other techniques for depth determination.