The atomic number densities of 87 Rb vapor and surrounding gas 3 He in a sealed cubic cell were measured by sweeping the absorption line and fitting the experimental data with a Lorentzian profile. The absorption was carried out around the D1 transition at different temperatures. We compare our results for the number density for 87 Rb with the previous methods and calculate the fractional error to be less than 5% as well as the error for 3 He between this work and the density obtained from the filling procedure to be no more than 4.2% at 370K. In addition, we discuss the factors that contribute to the error, among which the cell temperature plays the most important role.
The atomic number densities of 87 Rb vapor and surrounding gas 3 He in a sealed cubic cell were measured by sweeping the absorption line and fitting the experimental data with a Lorentzian profile. The absorption was carried out around the D1 transition at different temperatures. We compare our results for the number density for 87 Rb with the previous methods and calculate the fractional error to be less than 5% as well as the error for 3 He between this work and the density obtained from the filling procedure to be no more than 4.2% at 370K. In addition, we discuss the factors that contribute to the error, among which the cell temperature plays the most important role.
Atomic density is a basic and important parameter in quantum optics, nonlinear optics, and precision measurement. In the past few decades, several methods have been used to measure atomic density, such as thermionic effect, optical absorption, and resonance fluorescence. The main error of these experiments stemmed from depopulation of the energy level, self-absorption, and the broad bandwidth of the laser. Here we demonstrate the atomic density of 87 Rb vapor in paraffin coated cell between 297 K and 334 K mainly using fluorescence measurement. Optical pumping, anti-relaxation coating, and absorption compensation approaches are used to decrease measurement error. These measurement methods are suitable for vapor temperature at dozens of degrees. The fitting function for the experimental data of 87 Rb atomic density is given.
The improved method for the determination of the atom number densities in pure and mixed alkali vapours has been proposed. In order to obtain the correct results one has to go beyond the simple Lorentzian shape of the quasistatic absorption profile. The method has been tested by the white-light absorption measurements in the pure K, Rb and Cs vapours. The statistical accuracy of the obtained data for the atom number density is +or-3%. The method has been applied for determining the atom number densities in the vapour over the Rb-Cs mixture. The obtained values have been used in the evaluation of the effective C 6 constants for Rb*-Cs interaction: C 6 eff =(4.9+or-0.3)* 10 -30 cm 6 s-1 for the D2 line. The theory predicts C 6 eff =4.95*10 -30 cm 6 s -1 for the D1 line and C 6 eff =2.37*10 -30 cm 6 s(-1) for the D2 line.
A new method and its principle are presented for measuring the each component gas pressures in Rubidium (Rb) by the analysis of absorption spectral profile. The experiment system is set up to obtain Rb absorption spectra. And then each component gas pressures in atom vapor cell is estimated. First, the relationships between transmittance of probe light, atom density and absorption cross section are introduced, and the factors which influence the absorption spectral profile and methods to measure gas pressures are given. Second, the frequency-dependence curves of transmittance and the absorption spectra are obtained through tuning the laser frequency through the Rb D1 transition. Finally, the gas pressures of Rb, N2 and He are achieved, through fitting absorption spectral profile referring to half-width and minimum transmittance value of absorption spectra. The experiment results show that gas pressures in Rb atom vapor cell can be accurately measured by absorption spectrometric methods, which will be helpful for the following study of atom vapor cell. The gas pressures of N2 and He measured by the experiments are well matched with design values. The Rb gas pressure is 30%~50% less than the saturated vapor pressure and the suppression may be due to the adsorption of the cell surfaces coated with octadecyltrichlorosilane (OTS) film.
We have made systematic studies of rubidium (Rb) number density and polarization with the purpose of comparing a variety of techniques used to make these measurements. We have used five different temperatures, 40°C to 100°C in 15° increments, to compare number density measurements made using optical absorption with those made using Faraday rotation. A diode laser operating in the region near the Rb D1 transition was used in the case of the former, while for the latter two different lasers were used, one each operating in the vicinity of the Rb D1 and D2 transitions. These number density results are compared with those obtained from vapor temperature formulae (e.g., Killian, CRC, etc.). We have also made a systematic study of Rb optical pumping using an amplified tunable diode laser which has been incrementally broadened in order to determine the effect of linewidth broadening on Rb polarization. We vary the frequency of the circularly-polarized pump laser across the D1 transition absorption profile for each of four linewidths (0.01, 0.5, 2, and 8 GHz) and measure the Rb polarization using Faraday rotation. The Rb number density for these measurements is on the order of 1012 cm−3, with 1 Torr of N2 as the buffer gas. These results are then compared with polarization measurements taken using a re-pump laser operating near the Rb D2 transition, and with theoretical calculations of the rubidium polarization.
The temperature of the alkali metal cell, which affects the density of the alkali-metal vapor and the gas pressure, is usually difficult to measure directly. However, the temperature of the alkali-metal cell and the density of the alkali-metal vapor are important parameters that affect the performance of the atomic sensor. In this paper, a device that can directly measure the internal temperature of an alkali metal cell in real time is designed for the first time to explore the relationship between alkali-metal vapor density and temperature. Alkali-metal vapor density is measured using the absorption spectrum. The pressure broadening model, combined with the transition of four hyperfine levels, was used to fit the absorption line of 87Rb D1 under the action of 700 Torr N2, and a good fitting effect was obtained. The experimental results show that the density of 87Rb is less than the value calculated by the empirical formula. Based on the experimental results, we give the calculation formula of 87Rb density with an uncertainty of only 4% and obtain the temperature dependence index of the line width and linear displacement of 87Rb in N2 by analyzing the absorption spectrum.
Micro-electro-mechanical systems (MEMS)-based (chip-scale) alkali vapor cells are key components in emerging quantum technologies, where device performance critically depends on the atomic number density. Thus, it is important to have an accurate estimate of the atomic number density in MEMS-based alkali vapor cells to optimize light-matter interactions and design efficient quantum sensing systems. Here, a quantitatively validated method is presented for determining the rubidium (Rb) atomic number density in warm vapor using Single-Pass Absorption Spectroscopy (SPAS). The absolute transmission spectra are measured and modeled using the 780.24~nm and 420.29~nm transitions in Rb-filled MEMS vapor. The theoretical model employs a density-matrix formalism within the Lindblad framework and incorporates directly measurable experimental parameters, such as laser beam power, diameter, and cell temperature. The model explicitly accounts for optical pumping, Doppler broadening, and transit-time broadening effects and exhibits quantitative agreement (>99%) with experimental spectra over a broad range of temperatures (293-353~K), laser probe powers of approximately 10~μW-100~μW at the 780.24~nm transition and 8~μW-80~μW at the 420.29~nm transition, and cell lengths (2--100~mm). This method demonstrates a practical and reliable approach for determining the density of alkali vapor cells for quantum sensing, metrology, and quantum communication applications.