LAUSR

Magneto-optical double-resonance magnetometers are attractive candidates for sensitive measurements of magnetic fields but suffer from a fundamental problem known as the ``dead zone'': certain magnetic field directions where the magnetometer loses its sensitivity. We present a dead-zone-free double-resonance magnetometer with a single linearly polarized laser, which keeps uniform signal amplitude and isotropic sensitivity among varying magnetic field directions. The isotropic magnetometer can be switched between two modes, i.e., ${M}_{z}$ mode insensitive to phase shifts and ${M}_{x}$ mode with a higher upper bound of bandwidth. The dead-zone-free magnetometer exhibits a magnetic field noise floor of $0.9\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ and $1.2\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ in ${M}_{z}$ and ${M}_{x}$ modes, respectively. The proposed double-resonance magnetometer, benefiting from its compact single-beam structure, isotropic sensitivity, and capability of dual modes, would be useful for high-sensitivity magnetic field measurements in mobile applications.