Infrared vertical external cavity surface emitting laser threshold quantum magnetometer

One of the most promising candidates to use as compact high sensitivity magnetometers is the Nitrogen-vacancy (NV) center, however traditional implementations of this technology are plagued by low collection efficiencies or poor signal contrasts of the optically detected magnetic resonance (ODMR). Laser threshold magnetometry (LTM) offers a path towards both efficient signal collection and high signal contrasts by taking advantage of near threshold laser dynamics. We demonstrate an infrared LTM using a vertical external cavity surface emitting laser (VECSEL) with an intra cavity diamond plate doped with NV centers. The VECSEL was tuned to the spin dependent absorption line of the NV centers, which tied the VECSEL output power to the magnetic field sensed by the NV centers. Furthermore, the contrast and the projected sensitivity limit are shown to improve when operating close to the lasing threshold. We measure a sensitivity of 7.5 nT/^√Hz between 10-50 Hz with a contrast of 18.4% and a projected photon shot noise limited (PSNL) sensitivity of 26.6 pT/^√Hz close to threshold. We also observe a saturable absorption-like effect near threshold, which further enhances the signal contrast and projected PSNL near threshold. A rate equation model for the VECSEL threshold magnetometer is described and is fit to mimic the observed threshold dynamics.