Fig. 5
a Power Spectral Density (PSD) of NV-doped ND fluorescence (in blue) and of the MPPC photodetector, without optical input signal (in green). The PSD, in dBV2/Hz, represents how the power of an optical signal, collected by the photodetector, is distributed across different frequency components. The flat spectral floor sets the fundamental noise limit on the measurement. The PSD in blue was obtained on ND bound in the TL after the migration and under magnetic modulation. We observe the NV fluorescence blinking at 120 Hz, as well as the first 3 harmonics (240, 360 and 480 Hz), and the shot noise limit at PSD\(_{\textrm{NV}}\) \(\approx\) − 90 dBV2/Hz. The PSD measured from the MPPC signal (in green) indicates the noise limit of the photodetector at PSD\(_{\textrm{MPPC}}\) \(\approx\) − 122 dBV2/Hz. b Evolution of the normalised fluorescence emitted by an europium molecule after its optical excitation. We consider a long fluorescence time of \(\tau _{\textrm{Eu}}~=~1~\textrm{ms}\), with a measurement of time \(\Delta t = 400~\mathrm {\mu s}\) performed at \(T_0 = 200~\mathrm {\mu s}\).
