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Qualification of optics

In production with lasers, for productivity reasons beam powers used are increasingly being increased up to the range of 6 to 8 or 10 kW and above. This leads to an increasing load on the optics used in the processing heads, in other words, power-dependent focus shift. The absorption properties and dirt contamination level of the optics are increasingly becoming an issue, along with quality assurance of the optics, for the manufacturers of the optics, processing heads and laser systems.

Measurement methods

The OpticsQualityMonitor enables the testing of the absorption properties of the optics by suppliers and fabricators, or users in quality assurance. This not only guarantees that the optics have been manufactured within the specifications, but also that they are equal to the requirements during their use. This allows manufacturing or handling errors in the manufacturing chain to be identified, and it guarantees that the optics can deliver their best performance in their use.

The OQM compares the absorption of a translucent optical element, for example from a processing head (lens or flat optics) with the absorption of reference optics (same type: material, refractive index, diameter, radii of curvature and anti-reflective coating). In this process, the heating occurring on the optics surface due to the laser power absorbed in the optics is measured.


The temperature measurement is performed without contact, i.e. there is no change at all in the optics through the measurement or the mounting of the optics during the measurement. This makes the OQM particularly suited to incoming or outgoing goods checks of optics used in high power ranges.

The measurement of the temperature increase in the optical surface enables comparative statements to be made in relation to the absorption of optics within a series production, between different series productions or between goods supplied by different suppliers. The absolute absorption value is not determined, however.

The OpticsQualityMonitor is supplied in a Class 1 laser housing with an integrated laser and cooler. The device is intended for operation in a cleanroom.

Technical data

Measurement system

  • 500 W single mode laser (1070 nm)
  • Pyrometer with 10 ms time constant and 10 mK resolution (12 to 16 µm)
  • Spot size of 2 mm on the measurement sample (both heat spot and measured spot)

Optics data

  • Diameter of sample up to 60 mm
  • Thickness of sample up to 25 mm
  • Radius of curvature great than 12 mm
  • Anti-reflective coating required

Capacity and accuracy

  • Testing capacity: around 4 optics per hour
  • Reproducibility: ± 0.1 K
  • No calibration of absolute absorbtion