In-situ measurement of magnetic field gradient in a magnetic shield by a spin-exchange relaxation-free magnetometer*
Fang Jian-Chenga), Wang Taoa)†, Zhang Hongb), Li Yanga), Cai Hong-Weia)
       
The second harmonic signal of the lock-in amplifier with different locations of the probe beam along the z direction. The different offsets of the curves are due to the unequal scale factor caused by different polarization rates. Moreover, when the pump beam’s power is larger than 60 mW, the alkali atoms are almost fully polarized, and the curves almost overlap.