Photothermal radiometry

Photothermal radiometry is a non-contact, non-destructive inspection method that is very well suited for the characterization of thin layers, hardening depths, grinding burn detection, and other challenging applications. This heat flow method is used particularly when extremely high measurement accuracy is required. The measurement using photothermics is much faster than a materialographic analysis using cuts, polishing and microscopy, and, after appropriate calibration, enables a real-time analysis of hardening depths. The process is used both in production and in research and development.

ForaTherm – no more cutting

  • Allows for non-destructive characterization of surface engineered components (after calibration)
  • Realtime inspection
  • From random sampling to 100% inline inspection

Principle of photothermal radiometry

The photothermal method is based on periodic surface heating using laser light. The modulated heat flows from the surface into the interior of the component, whereby the heat flow is influenced by the material properties and the sample geometry. An infrared detector continuously records the radiation intensity-proportional signal from the surface, which is analyzed by a lock-in amplifier for amplitude and phase. The phase can be linked to certain material parameters such as hardness or layer thickness by means of calibration measurements. This requires both photothermal measurements and a subsequent destructive test of representative reference samples. For imaging measurements, the components must be scanned.

Typical ForaTherm applications

simulated grinding burn on reference body
Grinding burn on gear wheel
Measurement of layer thickness of a FeNi layer on silicon
case hardening depth in 16MnCr5


  • Measurement of case hardening depth (chd)
  • Measurement of layer thickness
  • Detection of grinding burn
  • Measurement of porosity in thin layers
  • Detection of missing adhesion of thin layers
  • Detection of covered corrosion

Foratherm Software

The software for controlling the laser and the kinematics and for data acquisition is customized.

Technical data

Wavelength808 nm
Bandwidth0.01 Hz – 200 kHz
Laser class4
Power supply230 V / 10A
Housing19” / 12 RU
Laser protectionoptional, e.g. L x W x H 1200 mm x 900 mm x 800 mm
Kinematicsoptional, e.g. xyz linear stages and rotation stage

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