Close-Loop Bell–Bloom Magnetometer with Amplitude Modulation

Abstract

A high sensitive optical amplitude modulation magnetometer is investigated and demonstrated experimentally. We build an experimental platform for the atomic magnetometer and configure it as a Bell–Bloom magnetometer with amplitude modulation of 50% duty cycle square waveform. The open-loop input-output model is deduced from the Bloch equation and is verified experimentally. Instead of locking the frequency by using a voltage control oscillator, we realize a closed loop using the coils to generate a feedback field which avoids the stringent requirement of a high resolution frequency meter and markedly expands the dynamic range as well as the bandwidth. We realize an open loop sensitivity of 0.8 pT/Hz1/2 at 20 Hz using a single light beam, which exceeds that of the state-of-the-art Bell–Bloom magnetometers, and the corresponding closed loop sensitivity is 1.2 pT/Hz1/2.

Suppression of mechanical error in micro-rotation-angle measurement of optical pumped atomic magnetometers

“…The extinction ratio can be reduced to 10 -5 by using Glan-Taylor polarizers. To improve detection precision, separate modulations are applied to the probe beam and the pump beam [1,9,11,[19][20][21][22][23]. However, the mechanical error, in an ideal case, is typically no less than 10 -3 rad [13], which is relatively large compared to the angle rotation caused by the weak magnetic field with alkali metal cells and requires calibration.…”

“…For the magnetometers with electron spin, the modulation of the pump beam is adopted to increase the sensitivity as well such as the ones with Bell-Bloom effect or with diamond [11,[19][20][21][22]. For the ones with modulation of the pump beam, the schematic is illustrated in figure 4.…”

An Atomic Magnetometer with Spin-Projection Noise Proportional to $\sqrt{{T}_{2}}$

“…The basic reason for this phenomenon is that when all the other atomic magne-tometers have optimized scale factors proportional to 𝑇 2 , that of SMoM is unrelated to 𝑇 2 in the transverse direction. For the main field, it depends on the used scalar magnetometry, which may be Bell-Bloom [15] or 𝑀 𝑥 magnetometer. [24] Fig.…”

Indirect pumping bell–bloom magnetometer

“…[1] Compared to the double resonance magnetometer, BBM has its advantage of being all optical, which does not produce any radio frequency fields, and has become an important type of atomic magnetometer. [2][3][4][5][6][7] The precession of the atomic spin polarization can be monitored by the paramagnetic Faraday rotation of another linearly polarized probe beam. [8] Such geometry is back-action evading and has the potential of achieving sensitivities beyond the standard quantum limit.…”