Low-coherence Interferometry

Tolerance-compliant manufacturing processes using adaptive process control through coaxially integrated sensor technology

© Fraunhofer IPT
External measuring head for high-resolution dimensional topography measurement based on short-coherence interferometry

Laser processing systems are increasingly establishing themselves as important tools for production in the industrial manufacturing of micro and macro components. Particularly in the manufacturing of microstructures, the laser can fully exploit its technical advantages such as its high precision and reliability, the variety of materials that can be processed, the extremely low thermal load on the components and the good automation capability

However, with low component tolerances and short cycle times, especially in high-precision applications in the field of ultra-short pulse lasers, laser processing often reaches its limits. Particularly in the manufacturing of precision components, even small changes in process parameters can result in the components produced no longer being within the specified tolerances. Thorough monitoring and precise control of the process is therefore indispensable.

For monitoring laser processes, the Fraunhofer IPT has developed a sensor system based on low-coherence interferometry that can be easily integrated into existing laser processing units. The light beam of the measurment system uses the same beam path that is used for the actual laser beam guidance. In this way, the modular inline measuring system can measure the component before, during and after processing. The measuring module offers high-resolution and submicrometric-accurate dimensional characterization of the surface geometries and is also capable of producing tomographic images of semi-transparent materials. In addition, low-coherence interferometry allows material and surface independent monitoring and adaption of the laser process.

Our services

  • Development of measurement systems and demand-oriented signal processing as well as feedback algorithms
  • Integration of the measuring systems into existing machines
  • Implementation of adaptive process control
  • Validation and characterization of the measurement process


topography testing

Low-coherent interferometry offers very high resolution for geometric distance measurements and achieves very high accuracies in the characterization of component features.

process control

Geometric data in the form of 3D point clouds can be returned directly to the laser system for adaptive process control using suitable feedback and control algorithms.



ESSIAL is concerned with the development of an inline sensor system for upscaling a laser micro structuring process for soft magnetic steels. By means of laser process control, surface structures can be produced in a targeted manner so that losses of electrical machines are reduced.


PoLaRoll is about the development of a polygon scanner-based roll-to-roll process for continuous and digital production of coated steel substrates. The IPT is developing an inline polygon scanner-based sensor system for feedback control of laser micro structuring.


Inline-process monitoring

(Kunze et al., 2017): Inline surface topography measurements of ultrashort laser pulsed manufactured micro structures based on low coherence interferometry, Fraunhofer IPT 2017.

Laser micromachining applications

(Kunze et al., 2017): Signal processing for in-line process monitoring for coaxially integrated metrology in laser micromachining applications, Fraunhofer IPT, 2017.


Laser Transmission Welding

(Schmitt et al., 2016): OCT for Process Monitoring of Laser Transmission Welding, Fraunhofer IPT, 2016.