Enhancing fluorescence excitation and collection from the nitrogen-vacancy center in diamond through a micro-concave mirror

Abstract

We experimentally demonstrate a simple and robust optical fibers based method to achieve simultaneously efficient excitation and fluorescence collection from Nitrogen-Vacancy (NV) defects containing micro-crystalline diamond. We fabricate a suitable micro-concave (MC) mirror that focuses scattered excitation laser light into the diamond located at the focal point of the mirror. At the same instance, the mirror also couples the fluorescence light exiting out of the diamond crystal in the opposite direction of the optical fiber back into the optical fiber within its light acceptance cone. This part of fluorescence would have been otherwise lost from reaching the detector. Our proof-of-principle demonstration achieves a 25 times improvement in fluorescence collection compared to the case of not using any mirrors. The increase in light collection favors getting high signal-to-noise ratio (SNR) optically detected magnetic resonance (ODMR) signals hence offers a practical advantage in fiber-based NV quantum sensors. Additionally, we compacted the NV sensor system by replacing some bulky optical elements in the optical path with a 1 × 2 fiber optical coupler in our optical system. This reduces the complexity of the system and provides portability and robustness needed for applications like magnetic endoscopy and remote-magnetic sensing.Negatively charged Nitrogen-Vacancy (NV) color center in diamond is a promising candidate for quantum information processing and spin-based quantum sensing of magnetic fields 1-3 , electric fields 4,5 and temperatures 6-8 . To efficiently use NV center in these applications, enhancing the excitation and collection of the color-center's fluorescence is demanded. For instance a high fluorescence collection efficiency would benefit precision metrology. Some methods; for example, circular gratings 9,10 or a solid immersion lenses (SIL) 11-13 , when fabricated on diamond substrates, extracts more fluorescence from a single NV center out of the high refractive index (∼2.4) material. While Micro/nanoresonator cavities and tapered optical fiber have been shown to enhance both the single NV center's fluorescence emission and couplingout efficiencies [14][15][16] . Similarly, optical antennas and plasmonic structures have been used to enhance the local light field thus improving the fluorescence efficiency through the Purcell effect, and enhance emission from a single NV defect in diamond 17,18 .Here, we demonstrate a simple method to enhance the excitation efficiency and also fluorescence collection from a micrometer-sized NV color-center rich diamond attached to the end of a sphered optical fiber. This singleport sensor configuration offers flexibility needed for some applications that require precision field-measurements in a non-standard location (e.g. magnetic endoscopy, subcutaneous measurements, remote and inaccessible loca-tions). Our enhancement technique is based on using a matched micro-concave (MC) mirror to a sphered opticfiber end.A diamond micro-crystal is fixed on the sphered tip op...

Integrated and Portable Magnetometer Based on Nitrogen‐Vacancy Ensembles in Diamond

“…This is in contrast to previous publications, where the fiber was used both for optical excitation and fluorescence collection. [ 29–32 ] For this purpose, we used a chip photodiode (Hamamatsu S12915‐33CHIP) with a photosensitive area of mm² and a responsivity of A W −1 (at 670 nm wavelength). A 1.45 µm thin distributed Bragg reflector (DBR) grown by chemical vapor deposition of several layers of amorphous silicon carbide (aSiC, ) and silicon oxide (SiO 2 , ) was deposited on the surface of the photodiode acting as a long‐pass filter to block the laser excitation light.…”

Toward Quantitative Bio-sensing with Nitrogen–Vacancy Center in Diamond

“…However, the lateral resolution was usually larger than 100 μm and thus not compatible with nanoscale measurements. Most recently, two optimized solutions of tapered optical fiber − and optical fiber with a photonic structure in the end , have been developed to gain a better spatial resolution (less than 10 μm). Furthermore, some approaches, e.g.…”

Efficient nitrogen-vacancy centers’ fluorescence excitation and collection from micrometer-sized diamond by a tapered optical fiber in endoscope-type configuration

“…In addition, this TOF tip can combine the microconcave technique 35 (locate the diamond attached on the TOF tip at the focal point of a matched microconcave mirror facing against the tip) to further enhance the fluorescence excitation and collection efficiency. As the micro-concave mirror can focus back the fluorescence emitted in the opposite direction of the TOF in a smaller incidence angle and the TOF has a relatively large fluorescence acceptance angle, this combining can greatly improve the system's fluorescence collection.…”