Speakers
Description
For SERF atomic magnetometer, photo-elastic modulator (PEM) is a commonly-used optical polarimetry technique to detect the weak angle signal due to its high sensitivity. Magnetic field to be measured can be obtained by demodulating the first-harmonic response signal from the photoelectric detector (PD) based on the modulation frequency of PEM. The optical rotation angle contains essential information including atom number density and transverse polarization, thereby accurate measurement of the optical rotation angle is very important. However, in previous studies, the optical rotation angle cannot be derived directly and quantitatively through the demodulated first harmonic signal. Therefore, we propose an in-situ measurement method of the optical rotation angle based on the dc and second harmonic components with PEM detection in SERF atomic magnetometer. We analyze the condition when a modulated linearly-polarized light can be derived by PEM. Further, we establish the expressions of the demodulated response signals by second-order approximation and verify our method by experiments. Our method does not introduce additional device and could be generally used in analysis of polarization and atom number density distribution. Moreover, our method is completely unaffected by the variation of the probe beam intensity and convenient for optical rotation angle measurement under PEM modulation in general optical systems, including but not limited to SERF magnetometer.
$U=k{{I}_{\text{probe}}}\left[ {{\varphi }^{2}}+\frac{1}{2}{{\alpha }_{\text{m}}}^{2} \right.+2\varphi {{\alpha }_{\text{m}}}\sin \left( 2\pi ft \right)\left. -\frac{1}{2}{{\alpha }_{\text{m}}}^{2}\cos \left( 4\pi ft \right) \right]$
${{\varphi }^{2}}=\frac{{{U}_{\text{dc}}}-{{U}_{2\text{nd}}}}{2{{U}_{2\text{nd}}}}{{\alpha }_{\text{m}}}^{2}$
The optical polarimetry measurement based on PEM in the SERF atomic magnetometer.
