Magneto-optical sensors

Magneto-Optical Visualization of Magnetic Fields

The highly sensitive magneto-optical (MO) sensors form the basis for visualizing magnetic fields in production and research.

Product Description

The magneto-optical sensors are available in sizes up to 60 x 45 mm2. Applications for the sensors include forensics and the quality control of magnetic materials.

Design & Function

The principle underlying magneto-optics is the Faraday effect. It describes the rotation of the plane of polarization of linearly polarized light passing through a transparent medium subjected to a magnetic stray field parallel to the direction of propagation of the light wave. If the light now passes through a magneto-optical medium to which a magnetic field is applied parallel to the direction of propagation of the light, it splits into two oppositely rotating, circularly polarized waves.

A phase shift now occurs for the two partial waves because they have different refractive indices and propagation velocities. Their frequency stays the same. This shift causes the polarization plane to rotate. When the circularly polarized partial waves emerge, absorption causes the creation of a common elliptically polarized wave. The different angles of rotation as a function of the magnetic field strength result in differences in contrast on the sensor, which can be evaluated optically. This achieves direct real-time visualization of static magnetic fields over the entire sensor area. The micrometer-thin MO layer provides the highest possible lateral resolution, depending on the optical system used.

The MO sensors are already standardly equipped with a mirror and an anti-scratch layer, making direct use in reflection mode possible.

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Magneto-optical sensors

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Product Highlights

  • Integrated mirror and scratch protection layer
  • Suitable for use in polarizing microscopes
  • Available in different sizes


  • Direct visualization of magnetic structures on the µm scale
  • Different sensitivities available
  • Lateral resolution down to the low µm range possible

Technical Specifications

Sensor geometries

  • Thickness: 0.5 mm
  • Chip size:
    • 8 x 8 mm²
    • 15.5 x 20.5 mm²
    • 45 x 60 mm²

Sensor characteristics

  • Resistance to temperature changes: up to +50°C
  • Working temperature range: up to +35°C
  • Optical resolution: up to 1 μm
  • Faraday rotation angle: (λ=590 nm) 1° to 10°

Sensor Type & Measuring range (kA/m)

  • A: 0.05 to 2.0
  • B: 0.4 to 55.0
  • C: 0.7 to 130
  • D: 0.03 to 5.0 (special for bias)

Application Areas

Sensor type A

Quality inspection & geometric assessment of:

  • Magnetic inks (banknotes, documents)
  • Domains in electrical steel
  • Security features for forensics purposes
  • Residual magnetism on production parts
  • Audio tapes
Sensor type B/C

Surface inspection and quantitative

  • Of permanent magnets
  • Of magnetic encoders
  • Of polymer bonded magnets
  • Of magnetic particles in composites
  • For superconductor examinations
Sensor type D

Examination and visualization of:

  • Soft magnetics
  • Magnetic inks in banknotes
  • Magnetic inks in documents



Magneto-optical visualization technology and systems

(936.0 KiB)

Magneto-optical Sensors

(351.5 KiB)

Application examples

Testing Floppy/Hard Disks

Visualizing Information Stored Magnetically on Data Media in Real Time

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Visualizing Domain Structures

Non-destructive Testing of Magnetic and Non-magnetic Materials

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Testing Magnetic Stripe Cards

Visualizing Barcode Structures in Real Time

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Controlling the Quality of Magnetic Solid Measures

Controlling Geometry and Field Intensity in Real Time

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Controlling the Quality of Permanent Magnets

Magnetic Field Visualization for Analyzing Homogeneity and Defects

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Verifying Document Authenticity

Rapidly Visualizing Magnetic Inks on Documents and MIRC-Encoded Checks

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Inspecting Weld Seams

Verifying Quality in Real Time and Without Damaging the Seam

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Analyzing Serial Numbers

Reading Out or Reconstructing Manipulated or Degraded Serial Numbers Non-destructively

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Testing Audio/Video Tapes

Forensically Examining Information Stored Magnetically on Data Tapes

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Verifying Banknotes

Analyzing Magnetic Security Features on Banknotes in Real Time

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Crack Testing on Ferromagnetic Components

Non-destructive Testing of Material Surfaces for Cracks

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