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Temperature dependent relaxation time of 87Rb atoms, namely the longitudinal relaxation lifetime T1 and the transverse relaxation lifetime T2 are studied respectively by using the Franzen method and by measuring the optical rotation of a weak, linearly polarized probe light. Although the Franzen measurement in this work is taken with a weak probe light, the absorption of probe light can still destroy the spin polarization of 87Rb atoms to a certain degree. However, a longer relaxation time of T2 can be well achieved by measuring the optical rotation of linearly polarized light under 6 GHz detuning along the direction of red light. Results show that both T1 and T2 obey an exponential decay with temperature, and the temperature dependent decaying rate of relaxation is respectively 27.8 for T1 and 25.0 for T2, indicating that temperature playing a similar role in the reaction to T1 and T2.

In this paper, the changes in chromaticity of LED lamps given by online test during accelerated aging under thermal stress were studied. Firstly, two online accelerated aging tests of a same type of lamps were conducted, with one test at the temperature of 60 ℃ and another at the temperature of 80 ℃. With the experimental data, the activation energy was obtained through the Arrhenius model, and then the accelerated aging time at the temperature of 80 ℃ equivalent to 6000 h aging at temperature of 25 ℃ was calculated. Secondly, the correlated color temperature (CCT) and color shift during accelerated aging test at the temperature of 80 ℃ were measured by both online test and offline test. It was shown that the increment amounts of CCT and color shift given by the online test were both about 20% higher than that given by the offline test. The t test and t’ test were used to verify the difference in chromaticity, which shows that the difference is of statistical significance. Therefore, the change of CCT and color shift given by the online test during accelerated aging can be used to judge the failure of lamps with some revision of the current criterions.

The lumen degradation of LED lamps undergoing an accelerated aging test is investigated. The entire LED lamp is divided into three subsystems, namely, driver, lampshade, and LED light source. The parameters of output power [Watts (W)], transmittance (%), and lumen flux (lm) are adopted in the analysis of the degradation of the driver, lampshade, and LED light source, respectively. Two groups of LED lamps are aged under the ambient temperatures of 25°C and 85°C, respectively, with the aging time of 2000 h. The lumen degradation of the lamps is from 3.8% to 4.9% for the group under a temperature of 25°C and from 10.6% to 12.7% for the group under a temperature of 85°C. The LED light source is the most aggressive part of the three subsystems, which accounts for 70.5% of the lumen degradation of the LED lamp on average. The lampshade is the second degradation source, which causes 21.5% of the total amount on average. The driver is the third degradation source, which causes 6.5% under 25°C and 2.8% under 85°C of the total amount on average.

The magnetic field is one of the most fundamental and ubiquitous physical observables, often conveying rich information about its generation source. Atomic magnetometers have been proven to be high-potential techniques for weak magnetic field measurement in various applications. However, due to the lack of excellent frequency-locking ability against abrupt magnetic field changes, atomic magnetometers are limited to use in application scenarios, which require both wide-range and self-locking characteristics. In this paper, theoretical and experimental research for a wide-range and self-locking rubidium atomic magnetometer based on free spin precession is presented. The rubidium atomic magnetometer can track a magnetic field jump of 10,000 nT in the measurement range from 500 nT to 100,500 nT. We also investigate the bandwidth and dead zone of the atomic magnetometer. An atomic magnetometer with excellent self-locking ability in a wide range can be developed into new highly sensitive magnetic measuring devices, enabling geomagnetic measurement in real environments and monitoring the magnetic phase transitions or coercive fields of soft magnetic materials in very magnetic-shielding environments.

We report a rubidium atomic magnetometer based on pump-probe nonlinear magneto-optical rotation. The rubidium vapor cell is placed in a five-layer magnetic shield with inner coils that can generate uniform magnetic fields along the direction of pump beam, and the cell is also placed in the center of a Helmholtz coil that can generate an oscillating magnetic field perpendicular to the direction of pump beam. The atoms are optically pumped by circularly polarized pump beam along a constant magnetic field in a period of time, then the pump beam is turned off and a /2 pulse of oscillating magnetic field for 87Rb atoms is applied. After the above process, the individual atomic magnetic moments become phase coherent, resulting in a transverse magnetization vector precessing at the Larmor frequency in the magnetic field. The linearly polarized probing beam is perpendicular to the direction of magnetic field, and can be seen as a superposition of the left and right circularly polarized light. Because of the different absorptions and dispersions of the left and right circularly polarized light by rubidium atoms, the polarization direction of probing beam rotates when probing beam passes through rubidium vapor cell. The rotation of the polarization is subsequently converted into an electric signal through a polarizing beam splitter. Finally, the decay signal related to the transverse magnetization vector is measured. The Larmor frequency proportional to magnetic field is obtained by the Fourier transform of the decay signal. The value of magnetic field is calculated from the formula:B=(2/) f, where and f are the gyromagnetic ratio and Larmor frequency, respectively. In order to measure the magnetic field in a wide range, the tracking lock mode is proposed and tested. The atomic magnetometer can track the magnetic field jump of 1000 nT or 10000 nT, indicating that the atomic magnetometer has strong locking ability and can be easily locked after start-up. The main performances in different magnetic fields are tested. The results show that the measurement range of the atomic magnetometer is from 100 nT to 100000 nT, the extreme sensitivity is 0.2 pT/Hz1/2, and the magnetic field resolution is 0.1 pT. The transverse relaxation times of the transverse magnetization vector in different magnetic fields are obtained, and the relaxation time decreases with the increase of the magnetic field. When the measurement range is from 5000 nT to 100000 nT, the magnetic field sampling rate of the atomic magnetometer can be adjusted in a range from 1 Hz to 1000 Hz. The atomic magnetometer in high sampling rate can measure weak alternating magnetic field at low frequency. This paper provides an important reference for developing the atomic magnetometer with large measurement range, high sensitivity and high sampling rate.