# A High-Sensitivity Cesium Atomic Magnetometer Based on A Cesium Spectral Lamp
## 2 Design and Construction of Cesium Atomic Magnetometer
### Electronic Unit  
The electronic unit components provide various functions for the sensor including temperature control, lamp RF excitation, and signal processing. They also transmit the Larmor frequency data to the frequency counting unit. The schematic diagram of the electronic unit is illustrated in Figure 2 and the details are described as follows. Figure 1: The sensor assembly of the cesium magnetometer. (**a**) Schematic of the sensor assembly; RF excitation (RF), lens (L), filter (F), circular polarizer (CP), feedback coil (FC), photodetector (PD). (**b**) Close-up of the working Cs lamp. (**c**) Larmor precession. (**d**) Emission spectrum of the Cs lamp after the filter, where the inset shows an enlarged plot of the main emitting line around the Cs D1 line (894.33 nm, in the air). The full-width-half-maximum (FWHM) linewidth is \(\sim\)0.35 nm (\(\sim\)130 GHz) by a Lorentzian fit. The D2 line (852 nm) has been significantly filtered. (**e**) Energy levels of Cs illustrating optical pumping, Zeeman splittings, and transverse magnetic field interactions. (1) RF Excitation Circuit  
The cesium spectrum lamp is excited by a \(\sim\)170 MHz RF signal from a discrete RF excitation circuit module. The current commercial atomic magnetometers, especially those based on alkali metal vapor cells, have a limited working temperature range of approximately \(-20\)\({}^{\circ}\)C to \(60\)\({}^{\circ}\)C. However, when the ambient temperature falls below \(-20\)\({}^{\circ}\)C, the sensor exhibits slow startup or even fails to function properly. The fundamental reason for this issue is the inability of the light source to operate at low temperatures. To address the temperature adaptability problem, a temperature feedback mechanism is introduced to improve the stability of maintaining the output RF power, particularly under different temperature conditions. In the circuit design, a thermistor is incorporated, as shown in Figure 3, in parallel with the voltage-divider resistors that control the frequency of the voltage-controlled oscillator and the power of the power amplifier. By controlling the voltage across the thermistor, which is in parallel with the control resistors, the output frequency and output power can be dynamically adjusted to compensate for the temperature variations. This ensures the stability of the RF excitation circuit output under different temperature conditions. Through a coaxial connection, the exciting coil of the lamp is connected to the RF excitation module, and an LC parallel resonance is used to inject energy into the lamp cell. (2) Temperature Control Circuit  
The temperature control circuit consists of two modules, one for controlling the temperature of the cesium spectral lamp and the other for the cesium vapor cell. The design scheme for both modules is the same. To avoid interference with magnetic field measurements, an AC heating method is employed. An AC heating signal with a frequency of 10 kHz is generated by a signal generator and driven by an audio power amplifier to heat the four twisted wires inside the sensor. The temperature detection circuit is responsible for monitoring the heating temperature, and the temperature control circuit implements  
Figure 3: Temperature feedback mechanism of cesium lamp. Figure 2: Schematic diagram of the electronic unit. the PI control. It adjusts the output power of the audio power amplifier by changing the amplitude of the signal generator, thereby controlling the temperatures of the lamp and the cell separately to the setting points. It is important to note that no thermistor is utilized to measure the cell's temperature directly, while the heating temperature is controlled using the electric bridge principle and the property that the resistance value of the heating wire changes with temperature. (3) Signal Processing Circuit  
To meet the requirements of motion platforms with a fast response speed, the self-oscillating magnetometer scheme is adopted in this work.