Alkali-metal vapor cells are key elements of atomic sensors. The temperature uniformity in the vapor cell is important for the sensitivity of the atomic sensors especially highly-sensitive SERF atomic magnetometers. This study proposes a novel double-layer cylindrical oven to improve the heating performance and the temperature uniformity of the vapor cell. We use the finite element method to build the thermal simulation models of the conventional square oven and the novel double-layer cylindrical oven. The performances of two ovens are compared. Then we build the experimental system to carry out the measurement experiment of heating temperature of the conventional and novel ovens and the in-situ measurement experiment of temperature distribution of the vapor cell using different ovens. We also measure the change of output signal amplitude of the SERF atomic magnetometer with frequency, i.e. the frequency response R(f) using the conventional and novel ovens respectively to evaluate the performance of the SERF atomic magnetometer using different ovens. The experimental results demonstrate that the proposed oven structure can improve the temperature uniformity of the alkali-metal vapor cell by 63.63% and the amplitude of R(f) using the novel oven increases by 24.7% on average. The novel double-layer cylindrical oven improves the temperature uniformity in the alkali-metal vapor cell and increases amplitude of the output signal of the SERF atomic magnetometer. The study is of great significance for improving the sensitivity of the atomic sensors especially SERF atomic magnetometers.
Alkali-metal vapor cells are key elements of atomic sensors. The temperature uniformity in the vapor cell is important for the sensitivity of the atomic sensors especially highly-sensitive SERF atomic magnetometers. This study proposes a novel double-layer cylindrical oven to improve the heating performance and the temperature uniformity of the vapor cell. We use the finite element method to build the thermal simulation models of the conventional square oven and the novel double-layer cylindrical oven. The performances of two ovens are compared. Then we build the experimental system to carry out the measurement experiment of heating temperature of the conventional and novel ovens and the in-situ measurement experiment of temperature distribution of the vapor cell using different ovens. We also measure the change of output signal amplitude of the SERF atomic magnetometer with frequency, i.e. the frequency response R(f) using the conventional and novel ovens respectively to evaluate the performance of the SERF atomic magnetometer using different ovens. The experimental results demonstrate that the proposed oven structure can improve the temperature uniformity of the alkali-metal vapor cell by 63.63% and the amplitude of R(f) using the novel oven increases by 24.7% on average. The novel double-layer cylindrical oven improves the temperature uniformity in the alkali-metal vapor cell and increases amplitude of the output signal of the SERF atomic magnetometer. The study is of great significance for improving the sensitivity of the atomic sensors especially SERF atomic magnetometers.
Alkali metal atomic cells are crucial components of atomic instruments, such as atomic magnetometers, atomic gyroscopes, and atomic clocks. A highly uniform and stable heating structure can ensure the stability of the alkali metal atom density. The vapor cell of an atomic magnetometer that uses laser heating has no magnetic field interference and ease of miniaturization, making it superior to hot air heating and AC electric heating. However, the current laser heating structure suffers from low heating efficiency and uneven temperature distribution inside the vapor cell. In this paper, we designed a non-magnetic heating structure based on the laser heating principle. We studied the temperature distribution of the heating structure using the finite element method (FEM) and analyzed the conversion and transfer of laser energy. We found that the heat conduction between the vapor cell and the heating chips (colored filters) is poor, resulting in uneven temperature distribution and low heating efficiency in the vapor cell. Therefore, the addition of graphite film to the four surfaces of the vapor cell was an important improvement. This addition helped to balance the temperature distribution and improve the conduction efficiency of the heating structure. It was measured that the power of the heating laser remained unchanged. After the addition of the graphite film, the temperature difference coefficient (CVT) used to evaluate the internal temperature uniformity of the vapor cell was reduced from 0.1308 to 0.0426. This research paper is crucial for improving the heating efficiency of the non-magnetic heating structure and the temperature uniformity of the vapor cell.
The number density of alkali atoms in vaper cell is an important parameter for atomic magnetometer. The vapor cell is usually heated to a high temperature for the number density exceed to 1018m−3to achieve the spin-exchange-relaxation-free (SERF) process. The optical rotation of multichannel atomic magnetometers is affected by the number density distribution. We present an effective method for monitoring and analyzing the spatial distribution homogeneity of the atomic number density in the alkali metal cell within the SERF magnetometer. The numerical results from researching the model of electric heating films and ovens show that the temperature gradient increases with an increase in the cell temperature. This causes an nonuniform number density distribution based on the saturated vapor pressure curve. We present a laser absorption spectroscopy method by using the high-resolution beam profiling camera to record the power of the beam before and after the cell. An optimized optical system of the atomic magnetometer has been established by measuring the the number density variation in the spatial distribution in mm scale. The number density variation coefficient, which is introduced to evaluate the distribution homogeneity, increases from 0.0257 to 0.0333 when the temperature of the oven wall rises from 140°C to 190 °C, showing the same trend as the simulation results. The optical rotation distribution is calculated according to the magnetometer output signal formula. This study is of great interest for optimizing the oven structure and improving the stability of atomic spin polarization and sensitivity of the multichannel magnetometer.
The SERF atomic magnetometer typically operates in a high-temperature and zero-magnetic-field regime. Among common heating methods, laser heating is a promising method since it is magnetically clean and stable. In this work, we for the first time introduce an orthogonal laser heating configuration to improve the temperature uniformity of the atomic cell, thereby enhancing the sensitivity of the atomic magnetometer. What’s more, a theoretical model is provided to illustrate the relationship between temperature variation and sensitivity. The temperature distributions of different laser heating configurations are evaluated by the finite element method. Experimental measurements were conducted with a single-beam atomic magnetometer. The spatial distribution of the conversion coefficient within the atomic cell was constructed through a simulation method. And the results show that, compared with the coaxial heating configuration, the orthogonal heating configuration improves the magnetic field sensitivity by 11.3%. Experimental results show that the magnetic field sensitivity under coaxial heating configuration is 56 f T / H z , while that under orthogonal heating configuration is 48 f T / H z , representing a 14.3% improvement. Both the simulation and experiments demonstrate that the orthogonal heating configuration significantly enhances the temperature uniformity within the atomic cell, thereby improving the magnetic field sensitivity of the atomic magnetometer.
Heating the alkali metal vapor cell to obtain high atomic density is a prerequisite for realizing the high-precision measurement for spin-exchange relaxation-free (SERF) co-magnetometer. However, the thermo-magnetic and thermo-optical coupling noise caused by the temperature diffusion from the alkali vapor cell is one of the main factors restricting the co-magnetometer performance at present. Here the influence of heating on the SERF co-magnetometer was comprehensively studied, and the thermal error model of the system was established. A novel heat insulation structure for the co-magnetometer was designed, and the effectiveness was verified through monitoring of characteristic temperature points. Compared to the conventional oven support, the average maximum temperature difference within 12 h of the optical path and magnetic shielding systems (OPMSS) decreased by 52%, the bias instability of the co-magnetometer decreased by 24%, and the noise of the co-magnetometer at 1 Hz decreased by 33%. The experimental results demonstrate that this method reduces the temperature fluctuation of the OPMSS, effectively suppresses the thermal coupling noise, and thus improves the performance of the SERF co-magnetometer. Moreover, this method is also applicable to other quantum sensors based on alkali metal vapor cell.
Wafer-level integration of micro heater on an alkali vapor cell for chip-scale SERF magnetometers is presented. In order to obtain a suitable resistivity, polysilicon and aluminum are mixed as the target material. Magnetron sputtering is adopted to fabricate the heater on the surface of the alkali vapor cell. Various voltages are applied to the heater, of which the temperatures are measured by thermal sensitive sensors. Spin exchange relaxation free (SERF) atomic magnetometer with the heater integrated on the alkali vapor cell is characterized. Results show that the micro heater is successfully integrated on the alkali vapor cell. With the integrated heater, the rubidium vapor cell is heated up to 120°C by a 445kHz AC current. The sensitivity of the SERF magnetometer is 6.3pT/Hz1/2. Results also indicate that it provides an effective and low-cost solution for the miniaturization of atomic magnetometers.
With the continuous improvement of weak magnetic detection technology, there has been a growing trend towards more compact and integrated magnetometer. The SERF magnetometer and the Mz magnetometer have many common features in operation. Therefore, we design a new kind of miniaturized atomic sensors to integrate the SERF magnetometer and the Mz magnetometer based on micro-fabricated alkali vapor cell. The sensor structure consists of alkali vapor cell, three-axis magnetic field coils, heating module and optical module. This small size sensor has the potential to achieve a portable multi-function device.