Learned from the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, the researchers proposed a new method for periodically pulsing the sodium continuous wave guide laser at the Larmor frequency between left and right circularly polarized states to achieve the magnetic resonance pumping of sodium atoms. Under the condition of resonant pumping, the high-altitude sodium atoms originally operating as "independent" rabbits are synchronized with each other, so that the sodium guide laser partially overcomes the influence of the geomagnetic field and effectively improves the optical pumping effect. Relevant research results have been published in "Science Report."
In the geomagnetic field, the sodium atoms that absorb the circularly polarized light make the Larmor precession around the magnetic field, greatly impairing the optical pumping effect. This is especially true when the included angle between the geomagnetic field and the laser beam is large, while in astronomical observations the angle is generally between 60 ° and 90 °.
In order to overcome the influence of the geomagnetic field, some researchers proposed a method of using the pulsed laser with a repetitive frequency of Larmor to carry out the resonance pumping so that the laser always interacts with the atom at a fixed time of the precession period. However, such a sodium guide star laser technology is difficult, has not been reported. The methods proposed by Shanghai Institute of Optics and Fine Mechanics are easy and effective. The difference between the two methods is that the precessional sodium atom is compared to the swing, the pulse method is equivalent to the cyclical one to the swing, and the polarization switching method is equivalent to Push and pull the swing periodically.
The numerical simulation results of the research group show that the echo flux increases with the angle between laser and geomagnetic field greater than 60 ° and the echo flux increases by 50% with the angle of 90 °. The method only needs to add a polarization conversion device in the optical path to achieve brightness enhancement, which can be directly used to upgrade the existing continuous-wave sodium guide laser system.
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