Rujie Li

Light intensity stabilization based on the second harmonic of the photoelastic modulator detection in the atomic magnetometer.

The fluctuations of the probe light intensity seriously affect the performance of the sensitive atomic magnetometer. Here we propose a novel method for the intensity stabilization based on the second harmonic component of the photoelastic modulator (PEM) detection in the atomic magnetometer. The method not only could be used to eliminate the intensity fluctuations of the laser source, but also remove the fluctuations from the optical components caused by the environment. A relative fluctuation of the light intensity of 0.035% was achieved and the corresponding fluctuation of the output signal of the atomic magnetometer has decreased about two orders of magnitude from 4.06% to 0.041%. As the scheme proposed here only contains optical devices and does not require additional feedback controlled equipments, it is especially suitable for the integration of the atomic magnetometer.

Polarization Measurement of Cs Using the Pump Laser Beam

In the optically pumped systems, the spin polarization of the atoms is generally derived by employing additional modulations, in which way an extra perturbation will be introduced and thus affect the normal operation of the sensors. By investigating the absorption principle of the circularly polarized pump laser, here, we demonstrate the feasibility of extracting the electron-spin polarization from the transmitted intensity of the pump beam. This scheme can detect real-time polarization without disturbing the normal operation of the sensor, and the experimental result agrees well with the theory. This research is of value to the research and development of optically pumped systems, especially the magnetometer, and the comagnetometer operated in the spin-exchange relaxation free regime.

Study of the operation temperature in the spin-exchange relaxation free magnetometer

We study the influence of the cell temperature on the sensitivity of the spin-exchange relaxation free (SERF) magnetometer and analyze the possibility of operating at a low temperature. Utilizing a 25 × 25 × 25 mm(3) Cs vapor cell with a heating temperature of 85 °C, which is almost half of the value of potassium, we obtain a linewidth of 1.37 Hz and achieve a magnetic field sensitivity of 55 fT/Hz(1/2) in a single channel. Theoretical analysis shows that fundamental sensitivity limits of this device with an active volume of 1 cm(3) could approach 1 fT/Hz(1/2). Taking advantage of the higher saturated vapor pressure, SERF magnetometer based on Cs opens up the possibility for low cost and portable sensors and is particularly appropriate for lower temperature applications.

The effect of hydrogen charging on Ln-based amorphous materials

In present work, the effects of hydrogen charging on Ln-based (Ln=La,Ce) bulk-metallic glasses (BMG) are studied. The (La0.5Ce0.5)65Al10Co25 were charged with hydrogen by an electrochemical method in an alkali solution. The hydrogen concentration in the sample after a 36 h charge can reach as high as 1286 w-ppm. With the presence of hydrogen atoms, the hardness of specimen increased by 80% compared to the as-cast samples. The structural evolution of the amorphous matrix due to the hydrogen-uptake process was investigated by the high-energy x-ray scattering technique. The sample surface was crystallized after hydrogen charging. X-ray diffraction measurements revealed broad crystalline peaks superimposed on an amorphous-scattering pattern. The crystalline phase grew from the surface to at least one hundred microns deep into the amorphous matrix. The atomic arrangements of both amorphous and crystalline phases were characterized by the atomic pair-distribution function.

Far off-resonance laser frequency stabilization using multipass cells in Faraday rotation spectroscopy

We propose a far off-resonance laser frequency stabilization method by using multipass cells in Rb Faraday rotation spectroscopy. Based on the detuning equation, if multipass cells with several meters optical path length are used in the conventional Faraday spectroscopy, the detuning of the lock point can be extended much further from the alkali metal resonance. A plate beam splitter was used to generate two different Faraday signals at the same time. The transmitted optical path length was L=50  mm and the reflected optical path length was 2L=100  mm. When the optical path length doubled, the detuning of the lock points moved further away from the atomic resonance. The temperature dependence of the detuning of the lock point was also analyzed. A temperature-insensitive lock point was found near resonance when the cell temperature was between 110°C and 130°C. We achieved an rms fluctuation of 0.9 MHz/23 h at a detuning of 0.5 GHz. A frequency drift of 16 MHz/h at a detuning of -5.6  GHz and 4 MHz/h at a detuning of -5.2  GHz were also obtained for the transmitted and reflected light Faraday signal.

A parametrically modulated dual-axis atomic spin gyroscope

We describe a dual-axis atomic spin gyroscope based on an alkali metal-noble gas comagnetometer. Alkali metal vapor is optically pumped, and then the noble gas is hyperpolarized along the z axis. When sensing a transverse rotation, the polarized noble gas will be induced to precess and produce an effective magnetic field in the x – y plane for alkali metals to precess under. Operating in the spin-exchange relaxation-free regime, alkali atoms are modulated by the z axis magnetic field and serve as an integrated in-situ dual-axis magnetometer to detect the gyroscopic precession in the x and y axes simultaneously, using a single probe beam. By using the parametric modulation technique, the low frequency drift is effectively suppressed and a bias instability of less than 0.05 deg/h has been achieved in our dual-axis atomic spin gyroscope.

A dual-axis, high-sensitivity atomic magnetometer*

Atomic magnetometer (AM) operated in a spin-exchange relaxation-free (SERF) regime features superior sensitivity and non-cryogenic operation, and thus is competitive with the best superconducting quantum interference devices. Previously, SERF AM with fT/Hz1/2 level sensitivity commonly acted as a single-axis sensor. Here we demonstrate a dual-axis SERF AM capable of simultaneously and independently detecting x- and y-field components with a sensitivity of 20 fT/Hz1/2. As there is no necessity to worry about the cross-talk effects arising from field modulations, the dual-axis scheme proposed here is of particular interest to AM array and hence the biomagnetic applications.

Measurement and cancellation of light shift in optically pumped magnetometers

Light shift arising from the circularly polarized pump beam in atomic magnetometers can induce an undesired magnetic response, and thus affect their accuracy. Here, the light shift and the corresponding cross-talk effect in the magnetometer have been investigated, and a scheme with an additional off-resonant pump beam with an appropriate polarization and intensity has been proposed to effectively reject the light shift. And the experimental results reproduce the expected behavior. This scheme provides a powerful tool to reject the light shift in optical pumping systems, in particular, the hybrid optically pumped systems.