In this article, we found an appropriate operating frequency of pump light for stabilizing the light frequency based on the atomic absorption of the vapor cell in the minimized atomic magnetometer. The traditional way to apply this stabilizing method is to stabilize the laser frequency at the absorption peak because its derivative is always zero and not affected by the cell temperature if the pressure shift is suppressed. However, it is observed experimentally that the response amplitude has a drop of up to 40% from the maximum at the absorption peak. It is due to the hyperfine optical pumping, and we explored the applicable condition to obtain the maximum response amplitude by solving the Liouville equation and proved it experimentally as well. Furthermore, we found that under the appropriate pressure, the frequency to obtain maximum response is close to the zero points of the second-order derivative which are not affected by cell temperature as well. Therefore, it is purposed to stabilize the pump laser frequency at these points. It is demonstrated experimentally that the frequency stabilization is the same, while the response amplitude is increased by more than 40% compared to stabilizing at the absorption peak. These results are instructive in improving the performance of minimized atomic magnetometers.
In this article, we found an appropriate operating frequency of pump light for stabilizing the light frequency based on the atomic absorption of the vapor cell in the minimized atomic magnetometer. The traditional way to apply this stabilizing method is to stabilize the laser frequency at the absorption peak because its derivative is always zero and not affected by the cell temperature if the pressure shift is suppressed. However, it is observed experimentally that the response amplitude has a drop of up to 40% from the maximum at the absorption peak. It is due to the hyperfine optical pumping, and we explored the applicable condition to obtain the maximum response amplitude by solving the Liouville equation and proved it experimentally as well. Furthermore, we found that under the appropriate pressure, the frequency to obtain maximum response is close to the zero points of the second-order derivative which are not affected by cell temperature as well. Therefore, it is purposed to stabilize the pump laser frequency at these points. It is demonstrated experimentally that the frequency stabilization is the same, while the response amplitude is increased by more than 40% compared to stabilizing at the absorption peak. These results are instructive in improving the performance of minimized atomic magnetometers.
The light shift represents a major source of measurement error and system noise in optically pumped atomic magnetometers (OPAMs). Tuning the laser frequency to a specific value is a common and effective approach to suppressing light shift in many optical-pumping systems. However, when this method is applied to OPAMs, a significant issue arises: at the zero-light-shift frequency, the magnetometer’s sensitivity decreases markedly. Consequently, it is not possible to optimize simultaneously both the measurement accuracy affected by the light shift and the overall sensitivity of the magnetometer. To address this contradiction, the underlying mechanism was analyzed using the theory of light absorption and the principles governing light–atom interactions, leading to the proposal of a dual-frequency optical-pumping scheme. Experimental results demonstrate that this approach can suppress the light shift by more than 95% while maintaining the optimal sensitivity of the OPAM. The proposed dual-frequency scheme can also be extended to other circularly polarized optical-pumping systems, thereby facilitating both the enhancement of OPAM performance and its practical deployment in real-world applications.
Precise laser stabilization is a fundamental aspect of modern metrology, directly influencing the accuracy of fundamental measurements in fields such as high-precision metrology, atomic sensor applications, and quantum technologies. Saturation absorption spectroscopy (SAS) is one of the most effective techniques for achieving high spectral stability, as it enables laser frequencies to be locked to atomic resonances. This technique exploits the nonlinear interaction between a weaker probe beam and a stronger pump beam within a rubidium (Rb) atomic vapor cell. By eliminating Doppler broadening, SAS allows well-defined hyperfine transitions to be resolved, providing a reliable optical frequency reference. This study aims to optimize laser frequency stabilization using the SAS technique by investigating the effects of laser light polarization, atomic vapor cell temperature, and pump-probe power adjustments. Polarization-dependent selection rules influence transition probabilities, thereby affecting spectral contrast and frequency stability. Additionally, atomic density variations, which depend on the vapor cell temperature, influence signal strength and linewidth, necessitating precise temperature control for optimal performance. Furthermore, the pump power must be sufficient to induce saturation without excessive power broadening, while the probe power must remain low enough to prevent spectral line distortion. By optimizing polarization, temperature, and power parameters, the stabilization of the Rb atomic laser can be enhanced, leading to improved reproducibility and consistency in high-precision measurements. SAS-based laser stabilization is particularly crucial for atomic sensor applications and quantum technologies, where highly stable, narrow-linewidth lasers are essential for precision measurements. Applications such as atomic magnetometers, gyroscopes, and inertial navigation systems depend on precisely stabilized lasers for optimal performance. By enhancing the reliability of laser frequency stabilization, this work contributes to the advancement of next-generation atomic sensors with improved sensitivity and stability.
The light shift is an important error source for atomic magnetometers. It would vanish if the frequency of the circularly polarized light is tuned to the optical resonance center. For high-density alkali-metal atomic magnetometers, the vapor cell has a large optical depth near the resonance, resulting in the difficulty in obtaining the exact resonance center by measuring the optical absorption line. In order to solve this problem, we propose a method to tune the pump light to a frequency where the shift is minimum based on the magnetic field zeroing technique. In addition, we also compare our results with the fitting center of the optical absorption line based on the measurement data far detuned from the resonance. The experimental results show that our method achieves a better suppression result of the light shift.
In order to measure a weak alternating magnetic field, an optically-pumped Rb magnetometer based on pump-probe structure is investigated and demonstrated. The pumping light and probing light propagate along the z axis and x axis, respectively. A constant polarization magnetic field along the pumping light is applied, which not only stabilizes the polarization of Rb atoms but also tunes resonance frequency of Rb atoms. When a weak alternating magnetic field is applied perpendicularly to the constant magnetic field, the magnetic moment will tip off the z axis and rotate around the z axis. And then the polarization plane of probing light is modulated correspondingly. The x component of the magnetic moment can be obtained with a balanced detector. As a result, a signal proportional to weak alternating magnetic field can be obtained.In order to obtain the magnetic response of the magnetometer, we analyze the signal amplitude as a function of polarization magnetic field strength B0 and transverse relaxation time 2 with numerical simulation. The amplitude-frequency response of the magnetometer is determined mainly by two parameters, namely cutoff frequency c=1/2 and resonance frequency 0= B0, where is the gyromagnetic ratio of Rb atom. At low frequency, that is a0 and a 0c2, the magnetometer has a flat response, here a is the frequency of the weak alternating magnetic field. If 0c, the signal amplitude will be large for large 0 or small c. For a given c, the peak response appears at 0=c. In the vicinity of resonance frequency, if c0, a peak will appear and if c 0, no peak occurs. At high frequency, the amplitude will decrease with the increase of a.We verify the above analyses in experiment. A vapor cell with a short transverse relaxation time is used to obtain large frequency response bandwidth. Through optimizing the powers and frequencies of pumping laser and probing laser, high polarization and detection sensitivity of atomic spin can be obtained. Moreover, through choosing an appropriate polarization magnetic field, the magnetometer can be maximally sensitive to the magnetic field to be measured. The experimental results show that the magnetometer has a sensitivity of about m 0.2; pT/HzHz and bandwidth of about 3.5 kHz. It can be used to detect low field magnetic resonance and high frequency abnormal physical phenomena.
The utilization of atomic or molecular spectroscopy for frequency locking of single-frequency laser to improve laser frequency stability plays an important role in the experimental investigation of optically pumped atomic magnetometers, atomic clocks, laser cooling and trapping of atoms, etc. We have experimentally demonstrated a technique for frequency stabilization of a single-frequency laser employing the bright state spectroscopy (BSS) with a rubidium atomic vapor cell. By utilizing the counter-propagating dual-frequency 795 nm laser beams with mutually orthogonal linear polarization and a frequency difference of 6.834 GHz, which is equal to the hyperfine splitting of rubidium-87 ground state 5S1/2, an absorption-enhanced signal with narrow linewidth at the center of Doppler-broadened transmission spectroscopy is observed when continuous scanning the laser frequency over rubidium-87 D1 transition. This is the so-called BSS. Amplitude of the absorption-enhanced signal in the BSS is much larger compared with the conventional saturation absorption spectroscopy (SAS). The relationship between linewidth and amplitude of the BSS signal and laser beam intensity has been investigated. This high-contrast absorption-enhanced BSS signal has been employed for the laser frequency stabilization. The experimental results show that the frequency stability is 4.4×10−11 with an integration time of 40 s, near one order of magnitude better than that for using the SAS.
We propose a far off-resonance laser frequency stabilization method that can accurately adjust the frequency lock points based on the Faraday rotation spectroscopy. The atomic magnetometer based on the spin-exchange relaxation-free (SERF) theory needs to stabilize the frequency of the probe laser on the detuning of several gigahertz (GHz) away from the resonance of the alkali metal atom, to reduce the absorption of the probe light by the alkali metal vapor cell. We propose a laser frequency stabilization method that can accurately adjust the frequency lock points using an acousto-optic modulator based on Faraday rotation spectroscopy. We reveal the principles of the method and simulate the new Faraday rotation spectra. Besides, we study the effect of the amount of frequency shift of the acousto - optic modulator and the temperature of the alkali metal vapor cell on the frequency lock points of the spectra, and give the formula for calculating the frequency point. Our proposed laser frequency stabilization method can stabilize the laser frequency on the detuning of several gigahertz (GHz) away from the resonance of the alkali metal atom and can adjust the frequency lock points quickly and accurately. This method can be used in atomic magnetometer, degenerate Raman sideband cooling (DRSC) and two photon excitation of Rydberg states.