A differential rate meter for real-time peak tracking in optically detected magnetic resonance at low photon count rates
Kapildeb Ambal, Robert D. McMichael
We describe a real-time data processing and frequency control method to track peaks in optically detected magnetic resonance of nitrogen-vacancy centers in diamond. This procedure allows us to measure magnetic field continuously with sensitivity ≈ 6 µT/Hz1/2 and to track resonances at sweep rates exceeding 110 µT/s. We use a custom-built differential photon rate detector and active feedback control (PID) to lock the microwave excitation frequency of the magnetic resonance. Our scheme covers a broad magnetic field range, limited by the frequency range of the microwave generator. This measurement procedure automates the processing of photon counters voltage pulse outputs, and it provides sensitivity that is comparable to traditional photon counting methods.