High-contrast absorption magnetometry in the visible to near-infrared range with nitrogen-vacancy ensembles

Magnetometry with nitrogen-vacancy (NV) centers in diamond has so far beenmeasured via emission of light from NV centers or via absorption at the singlet transition at 1042nm. Here, we demonstrate a phenomenon of broadband optical absorption by the NV centersstarting in the emission wavelength and reaching up to 1000 nm. The measurements are enabledby a high-finesse cavity, which is used for room-temperature continuous wave pump-probeexperiments. The red to infrared probe beam shows the typical optically detected magneticresonance (ODMR) signal of the NV spin with contrasts up to 42 %. This broadband opticalabsorption has not yet been reported in terms of NV magnetometry. We argue that the lower levelof the absorbing transition could be the energetically lower NV singlet state, based on the increasedoptical absorption for a resonant microwave field and the spectral behavior. Investigations ofthe photon-shot-noise-limited sensitivity show improvements with increasing probe wavelength,reaching an optimum of 7.5 pT/√Hz. The results show significantly improved ODMR contrastcompared to emission-based magnetometry. This opens a new detection wavelength regime withcoherent laser signal detection for high-sensitivity NV magnetometry.