Magneto-Optical Crystals: TGG

TGG (Terbium Gallium Garnet Crystal) is an excellent magneto-optical crystal used in various Faraday devices (Polarizer and Isolator) in the range of 400nm-1100nm, excluding 475-500nm.


  • TGG has twice the Verdet constant of a terbium-doped glass.
  • The thermal conductivity of crystalline TGG is an order of magnitude greater than a typical glass.
  • Optical losses are lower for TGG than Tb-doped glasses.
  • The combination of the above factors make TGG better suited to high average power applications. The principal limiting factor is thermally induced beam distortion. Beam distortion is less for TGG than Tb-doped glasses under the same power loading level.


Formula Tb3Ga5O12
Crystal Structure [111]
Verdet Constant (632 nm) -134 RadT-1m-1
Verdet Constant (1064 nm) -40 RadT-1m-1
Thermal Conductivity 7.4 W cm-1 K-1
Refractive Index 1.95
Nonlinear Index, n2 8
Figure of Merit, V/a 27
Figure of Merit, V/n2 5


Orientation [111] within ±15 arc min
Wave Front Distortion < 1/8 wave
Extinction Ratio > 30dB
Diameter +0.00mm/-0.05mm
Length +0.2mm/-0.2mm
Chamfer 0.1mm @ 45°
Flatness < 1/10 wave at 633nm
Parallelism <10 arc secs
Perpendicularity < 5 arc min
Surface Quality 10/5 Scratch/Dig
AR coating R<0.2%  AR @1064nm
Barrel Finish (10-6 inches) 55 ± 5




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