Abstract
We demonstrate the use of spatial emission patterns to measure magnetic fields. The directional aspect of the Hanle effect gives a direct, visual presentation of the magnetic fields, in which brighter fluorescence indicates larger fields. It can be used to determine the direction as well as the magnitude of the field. It is particularly well suited for characterizing and aligning magneto-optical traps, requiring little or no additional equipment or setup beyond what is ordinarily used in a magneto-optical trap, and being most sensitive to fields of the size typically present in a magneto-optical trap.
Highlights
While most Hanle effect studies focus on depolarization, the interaction of atoms with magnetic fields affects the spatial pattern of the scattered light[8,10,11,12]
Because the effect saturates at about the same field magnitude which defines the edge of the trapping region, the size of the dark spot in the fluorescence gives an estimate of the size of the magneto-optical trap (MOT) trapping volume
One of the most useful advantages is that it gives a direct visualization of the fields, including the location of field zero crossings and an estimate of the size of the MOT trapping volume
Summary
While most Hanle effect studies focus on depolarization, the interaction of atoms with magnetic fields affects the spatial pattern of the scattered light[8,10,11,12]. If a magnetic field is present, the dipole oscillation axis will rotate around the field, changing the polarization of the emitted light Averaged over time, this reduces the scattered light polarization. The oscillating dipole emits with a sine-squared dipole emission pattern, and a detector displaced from the atoms in the driving light polarization direction will measure no scattered light. The strength of the field determines the rotation rate, and the rotation rate, compared to the decay time, determines the average light intensity scattered in the direction of the pump light polarization An example of this can be seen, which shows fluorescence from atoms in a region with 3 field zero points[25]. Note that the directional Hanle effect provides a picture of the field strength, viewable with a camera or directly viewable by eye
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