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

TL;DR

This paper presents a simple fiber-based micro-concave mirror method that significantly enhances fluorescence collection from NV centers in diamond, improving signal quality and system compactness for quantum sensing applications.

Contribution

The authors introduce a micro-concave mirror technique that boosts fluorescence collection efficiency and system portability in fiber-based NV quantum sensors.

Findings

Achieved 25-fold increase in fluorescence collection efficiency.

Enhanced signal-to-noise ratio in optically detected magnetic resonance.

Reduced system complexity with fiber optical components.

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 1x2 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.