Magnetometry with nitrogen-vacancy ensembles in diamond based on infrared absorption in a doubly resonant optical cavity

We propose to use an optical cavity to enhance the sensitivity of magnetometers relying on the detection of the spin state of high-density nitrogen-vacancy ensembles in diamond using infrared optical absorption. The role of the cavity is to obtain a contrast in the absorption-detected magnetic resonance approaching unity at room temperature. We project an increase in the photon shot-noise limited sensitivity of two orders of magnitude in comparison with a single-pass approach. Optical losses can limit the enhancement to one order of magnitude which could still enable room temperature operation. Finally, the optical cavity also allows to use smaller pumping power when it is designed to be resonant at both the pump and the signal wavelength.