基于原子吸收光谱的碱金属气室内多种混合气体压强测量方法

碱金属气室是基于原子无自旋交换碰撞弛豫的超高灵敏惯性和磁场测量装置的核心敏感器件。碱金属气室内气体的含量会对原子的弛豫以及系统其他参数的选取产生很大的影响，因此精密测量气室内混合气体各自的压强具有重要的意义。当气室内存在气体时谱线会出现压力展宽和频移，且压力展宽远大于自然展宽和多普勒展宽，因此仅考虑压力展宽。利用压力展宽、频移的大小与气体压强存在的函数关系，提出一种基于原子吸收光谱的碱金属气室内多种混合气体压强测量方法。通过扫描碱金属原子的吸收光谱，得到光学深度曲线，并用洛伦兹函数对其拟合，测得多种混合气体引起的单种碱金属原子的混叠压力展宽和频移，再根据已知的单种、单位压强气体引起的单种碱金属原子的压力展宽和频移，联立计算得到多种气体各自的压强。当存在n种碱金属时，最多可以测量4n种混合气体的压强。仿真结果表明，该方法适用于入射激光未被原子完全吸收的情况；激光功率和频率的波动在1%～10%的数量级时，测量精度影响低于0.4%的数量级，而温度波动在1%～10%的数量级时，测量精度影响高达30%的数量级。

Pressure Measurement of Each Gas in Alkali-Metal Vapor Cell with a Mixed Gas Based on Saturated Absorption Spectrum

Alkali-metal vapor cell is one of the most important core component. As a sensitive device, it is often applied in the measuring device of the ultra-high sensitive inertial and magnetic field, which is based on the atomic spin exchange relaxation free regime. The content of the gas in the alkali-metal vapor cell will have an enormous influence on the relaxation of the atoms and the selection of other system parameters. Therefore, the precise measurement of each gas pressure is of great significance. Pressure broadening and frequency shift will occur when there is gas in the alkali-metal vapor cell. We merely took pressure broadening into account, because pressure broadening was much larger than the natural broadening and Doppler broadening. Since both pressure broadening and frequency shift had a function relationship with the gas pressure, we proposed a method and experimental equipment to measure gas pressure based on saturated absorption spectrum. Firstly, we obtained the optical depth curve by scanning the absorption spectrum of alkali metal atoms, and fitted the curve by Lorenz function. We were able to obtain the superimposed pressure broadening and frequency shift of single alkali metal atom, which was caused by mixed gases in the cell. Then, we solved the simultaneous equations to get the pressure of each gas, based on the known pressure broadening and frequency shift of single alkali metal atom, which were caused by a single type and specific pressure gas. The maximum number of gas pressure we can measure was 4n in the mixed gas, when there was n kinds of alkali metal atoms. Simulation results showed that the method was applicable when the incident laser was not completely absorbed. The effect on measurement accuracy caused by laser power and frequency fluctuations is insignificant. Temperature fluctuation is very significant. We should take measures to achieve the accurate control of temperature.