Enhancement of fluorescence from nitrogen-vacancy center ensemble in bulk diamond with broadband antireflection coatings

The negatively charged nitrogen-vacancy (NV-) center in diamond is a promising platform for quantum sensing. However, fluorescence from the NV- centers suffers large energy loss at the diamond-air interface. Here, we propose a broadband antireflection coating to enhance the fluorescence intensity by simultaneously reducing the energy loss of the excitation laser and the fluorescence. The reflectance for normal-incidence light decreases from nearly 17% for bared diamond to below 0.33% for coated diamond in the wavelength range 500 nm-800 nm. The reflectance averaged over the fluorescence bandwidth is below 3% for angles of incidence less than 20°. The measured emitted fluorescence for the coated diamond is 1.44 times that of uncoated diamond, corresponding to nearly 20% improvement in the measurement sensitivity. The proposed method is significant for enhancing the signal-to-noise ratio of NV-based sensors.