Precise measurements of Faraday rotation using ac magnetic fields
Experimental setup. After passing the polarizer P, the laser beam is focused on the sample by a lens L. It is then made parallel again with a second lens and then traverses the analyzer A. Finally, it is directed through an interference filter IF at the photodiode (PD). The lock-in drives the magnetic coil through the amplifier and detects the signal from the PD at the same frequency.
Lock-in signal R versus the lock-in phase for different frequencies generated by the lock-in during the measurement of Faraday rotation in 1-mm-thick BK7 glass plate. Although the patterns should be random, the correlation between and is visible in the data.
(a) Skewed Faraday rotation distribution from 1-mm-thick BK7 glass (1000 data points per frequency) when signal leaks from the voltage amplifier to the photodiode. (b) Faraday rotation from the same material, after placing the photodiode on an independent power supply. Because of the significant signal-to-noise improvement, 50 points per frequency were sufficient. The mean is indicated by full squares, the boxes enclose 25-75% of the points, the median is indicated by a line in the middle of the boxes, 99% of the points are between cross signs and the dashes designate the maximum and minimum.
(a) Lock-in signal as a function of the average light intensity for different magnetic fields generated at in thick BK7 glass. (b) Lock-in signal as a function of the magnetic field at different average light intensities in thick BK7 glass.
(a) Faraday rotation per Oe, as a function of average light intensity in thick BK7 glass. (b) Faraday rotation per average light intensity, as a function of the magnetic field in thick BK7 glass.
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