A compact, high-sensitivity magnetometer, including: an optical interface to accept a linearly polarized first light; a pump light source to produce a circularly polarized pump light; a vapor cell having a sealed vessel containing an alkali-metal gas, a first input port to receive the first light, a second input port to accept the pump light from a direction perpendicular to the first light, and an output port to produce a second light; an electromagnetic source to apply a modulated electromagnetic field to the vapor cell at a direction perpendicular to the first light and the pump light, without using a modulator external to the vapor cell; a second linear polarizer, polarized perpendicular to the first light, the second polarizer to receive the second light and to produce a third light; and a photodetector to receive the third light, to produce an intensity measurement of the third light.