Faraday magneto-optical rotation instrument based on the axial uniform magnetic field generating device with magnetic columns and experimental design
[Objective]The Faraday magneto-optical rotation instrument,commonly used to study the magneto-optical rotation effect,has a crucial component:the axial magnetic field generation device.Traditional methods for generating this magnetic field include electromagnets and energized solenoids,which,while easily adjustable by changing the electric current,are bulky and prone to large noise fluctuations.Therefore,improvements to the Faraday magneto-optical rotation instrument are necessary.In addition,traditional Faraday magneto-optical rotation experiments with the"extinction method"tend to have large errors owing to their insensitivity to light intensity changes at the extinction position.Therefore,exploring other methods to improve measurement precision is necessary.[Methods]In our Faraday magneto-optical rotation instrument,we improved the uniformity of the magnetic field by symmetrically placing magnetic columns around the test samples.These columns consist of many small cylindrical NdFeB permanent magnets magnetized along their thickness.The magnetic field's strength can be conveniently adjusted by changing the number of magnetic columns.Compared with popular electromagnet devices,our designed magnetic field generator offers a stable magnetic field distribution and flexible magnitude adjustments.For precise measurement of Faraday magneto-optical rotation angle,we proposed and demonstrated a"phase method"instead of the traditional"extinction method."This method measures the rotation angle as a laser passes through TGG crystals once or twice.We also used a laser with different wavelengths,namely 405,450,520,and 635 nm,to measure the Verdet constant of TGG crystals.[Results]Experimental data indicated that the uniformity of the magnetic field was in the region of 5 cm along the axis.Higher axial magnetic field strengths corresponded to better uniformity,with an experimental unevenness measured at about 2.5％when the magnetic field exceeded 500 Gs.The"phase method"significantly improved the measurement accuracy of Faraday's rotation angle compared to the traditional"extinction method."In addtion,the rotation angle of a laser passing through a TGG crystal on a round trip was twice that of the laser passing through it once.It was successfully verified that when a linearly polarized laser enters the magneto-optical medium parallel to the axial magnetic field direction,the rotation direction of its polarization plane is determined solely by the magnetic field direction,not the laser's propagation direction.[Conclusions]The improved magnetic field generator flexibly controls the axial magnetic field within the range of 0-1000 Gs,maintaining good magnetic field uniformity.This device also meets the requirements for other magneto-optical rotation experiments,such as Faraday anomalous dispersion atomic optical filters.Moreover,the proposed"phase method"for measuring the rotation angle and the extinction position is accurately determined by mathematical software fitting data,significantly improving accuracy and reducing errors to less than＜0.5°.
Faraday magneto-optical effectuniform magnetic fieldVerdet constant
万方数据
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