Towards room-temperature laser magnetometry with NV centres in open fibre cavities

Summary form only given. Magnetic sensing with lasing from negatively charged nitorgen-vacancy (NV) centres in diamond is predicted to reach fT/SRHz regime even at room temperature [1]. Stimulated emission from NV centres has already been explored as a stepping stone towards such a laser magnetometer [2, 3, 4]. Here we report the observation of amplification on the cavity transmission of an open fibre cavity formed between a fibre-mirror and a macroscopic mirror, loaded with a high NV density diamond sample. On adding green laser light to optically pump the NV centres, we observe amplification on the transmitted seed wavelength close to 720 nm up to a factor around 3.