# A High-Sensitivity Cesium Atomic Magnetometer Based on A Cesium Spectral Lamp
## 1 Introduction  
Atomic magnetometers, which are based on the principles of Larmor precession of spin-polarized atomic vapor and optically detected magnetic resonance, are quantum precision measurement sensors for measuring weak magnetic fields [1]. In addition to various vibrant application fields such as magnetocaphelography [2] and frontier fundamental physics [3, 4], they are also regarded as the most sensitive scalar magnetometers for geomagnetic measurements [5, 6]. They have some advantages such as high sensitivity for low-frequency fields, high absolute accuracy, high stability, and resistance to platform orientation effects. Currently, they serve as the primary sensors in scalar magnetic exploration systems for applications such as underwater target detection [7, 8], unexploded ordinance [9], and airborne geological exploration [10]. In 1962, the first atomic magnetometer was developed by [PERSON] based on alkali metal elements using the optically detected magnetic resonance method [11]. Since then, atomic magnetometers exploiting numerous schemes have been the subject of extensive research and applications. In 2014, Geometrics Inc. launched a cesium optically pumped magnetometer (G-824A) with a sensitivity of 0.6 \(\mathrm{pT}/\sqrt{\mathrm{Hz}}\) and an operation temperature range of \(-30\)\({}^{\circ}\)C to \(50\)\({}^{\circ}\)C [12]. In 2017, QuspinInc. released a chip-scale atomic magnetometer (QTFM), based on a non-magnetic vertical-cavity surface-emitting laser (VCSEL) and micro-electromechanical system (MEMS) atomic vapor cell. It achieved a sensitivity of approximately 1 pT/\(\sqrt{\mathrm{Hz}}\) and a power consumption below 3 W [13]. In 2020, a cesium atomic magnetometer with a sensitivity of 0.6 pT/\(\sqrt{\mathrm{Hz}}\) was also reported by [PERSON] et al. [14]. The G-824A and QTFM represent two technological directions in the current development of atomic magnetometers for geomagnetic applications. The former aims for higher sensitivity to improve the detection capability of the sensor and its exploration system, while the latter focuses on low power-consumption and miniaturization to meet the application requirements of unmanned platform magnetic detection systems. Both directions have extensive application prospects in different scenarios. More recently, two types of atomic magnetometers exploiting new schemes have been demonstrated under the geomagnetic environment [15; 16]. Conducting research on high-sensitivity atomic magnetometer technology and improving its engineering applicability are of significant importance in enhancing the detection capability of magnetic survey systems, especially in challenging environments [17; 18]. In response to the temperature and sensitivity requirements for outdoor applications of geomagnetic surveys, a high-sensitivity self-oscillating cesium atomic magnetometer based on a cesium spectral lamp with a wide operating temperature range (\(-50\)\({}^{\circ}\)C to 70\({}^{\circ}\)C) is proposed and demonstrated in this paper. By introducing a temperature feedback mechanism, fluctuations in the excitation frequency and output power of the cesium lamp caused by temperature variations are substantially reduced, thereby resolving the issue of slow startup or the inability to operate at low temperatures. In respect of assessing the fundamental quantum limit sensitivity of the cesium magnetometer, the intrinsic relaxation rates in the Earth's magnetic field are evaluated. Moreover, the optimized cell temperature and feedback magnetic field amplitude are selected to improve the magnetometer' sensitivity. The design, simulation, and integration of the atomic magnetometer are conducted in this study, and the performance of the prototype is tested. The testing results indicate that the magnetometric sensitivity approaches 140 fT/\(\sqrt{\mathrm{Hz}}\) at 1 Hz, a factor of \(\sim\)1.5 above the photon-shot noise limit, confirming the technological advancement and applicability of this sensor for magnetic anomaly detection applications.