Laser threshold magnetometry using green light absorption by diamond nitrogen vacancies in an external cavity laser

Nitrogen vacancy (NV) centers in diamond have attracted considerable recent interest for use in quantum sensing, promising increased sensitivity for applications ranging from geophysics to biomedicine. Conventional sensing schemes involve monitoring the change in red fluorescence from the NV center under green laser and microwave illumination. Due to the strong fluorescence background from emission in the NV triplet state and low relative contrast of any change in output, sensitivity is severely restricted by a high optical shot noise level. Here, we propose a means to avoid this issue, by using the change in green pump absorption through the diamond as part of a semiconductor external cavity laser run close to lasing threshold. We show theoretical sensitivity to magnetic field on the pT/sqrt(Hz) level is possible using a diamond with an optimal density of NV centers. We discuss the physical requirements and limitations of the method, particularly the role of amplified spontaneous emission near threshold and explore realistic implementations using current technology.