Faraday effect

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