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Faraday effect
1) Passive polarizing elements
2) Faraday rotation
3) rotators, isolators, compensators
4) Magnetic field measurements
1) Passive polarizing elements
Anisotropic absorption: polarizers
Anisotropic index (crystals) birefringence, waveplates
Optical activity
= difference in index for the two different circular components
Principle of reciprocity applies
n of the order of 10-4
Birefringence: n of the order of 10-2
2) Faraday rotation
Rotation of the plane of polarization proportional to a magnetic field
Resonant effect:
n
+-
J=1
J=0
m=-1
m=+1
Difference between sublevels proportional to magnetic field.
2) Faraday rotation
The dispersion of any line extends very far (Lorentzian)ANY transparent medium has a Faraday effect.
Rotation is
At 790 nm, for TGG:V = 4.5×103oT−1 m−1
BK7 glass: 150
3) rotators, isolators, compensators
saturableabsorberdye jet
GTGG
Magnetic material of length l:
lTGG = Terbium Gallium Garnet
9 mm TGG 30 nT/Hz
Resolution: 10 nT or Faraday rotation of 8x10-9radSlope sensitivity inversely proportional to size
Femtosecond temporal resolutionExtracavity pumpIntracavity probe
Actual measurement
IPI
saturableabsorberdye jet
TGG l
Resolution:
8x10-9rad
Faraday rotation
0.3 Hz, for 9 mm TGG
IMPOSSIBLE TO MEASURE!
B = 10 nT
vs
80 MHz
temporal resolution
G
Intensity and time dependence of magnetic material:
Measure beat note as a function of position
l
Pump Probe experiment: External pump, internal probe