Characteristics and Advantages of Faraday Isolators

High Isolation

The properties of the Faraday isolator are determined by the quality of the optical elements and the uniformity of the magnetic field. The entrance and exit polarizers
ex­hibit a very high extinction ratio, so that the isolation is mainly limited by inhomogenieties in the crystal material. Specially selected crystal materials with a high Verdet constant and permanent magnets with a high remanence enable us to use a shorter crystal and obtain an isolation > 30dB.

The radiation blocked by the entrance and exit polarizers is not absorbed internally, but is deflected by 90° with respect to the beam direction. This ensures a stable thermal operation even at higher laser power levels. The blocked radiation can be used for other applications.

All optical surfaces are slightly tilted relative to the beam axis.

Low Insertion Loss

The high transmission, typically > 90%, is achieved by using absorption free materials and antireflection coa­tings on all entrance and exit faces with low residual reflectivity.

Large Aperture, Compact Design

The optical elements have been aligned to eliminate beam shading and allow for easy adjustment. Focussing is not necessary.

The compact design is achieved by using rare earth magnets with the highest remanent magnetism and TGG crystal material with a high Verdet constant.

The isolator is usable with divergent beams or when space is limited, a minimal optical path length in the isolator results in the lowest possible influence on the image.

Mounting Flexibility

Three sides of the entrance and exit polarizers are usable and readily accessible for easy cleaning. The degree of isolation can be adjusted in a wide range.

The isolators are mounted directly via threads in the casing or via additional base plates or angle brackets.

Applications

The ongoing development and refinement of laser tech­no­logy has created a need for optical components that shield the laser resonator from back reflections. Faraday isolators provide an efficient method of sup­pressing instabi­lities and intensity fluctuations in laser devices.

Typical applications are:

• protecting the resonator in solid state and gas lasers from back reflections
• preventation of parasitic oscillation in multistage solid state amplifiers
• protecting diode lasers against back scatter and extraneous light