Measuring position and dimension of the focus

The LaserQualityMonitor (LQM) is a perfect measurement system for the charaterization and qualification of the beam propagation of lasers in the range of UV to NIR.

Furthermore, errors in the optical assembly of resonators and beam guiding systems are easily analyzed.

Typical areas of application are:

  • Laser development
  • Quality assurance in production of laser sources
  • Service and maintenance

Determine beam propagations, analyse faults

With the LaserQualityMonitor PRIMES offers an integrated solution for the quick and straightforward analysis of the beam properties of a beam source. The beam propagation of lasers from the UV to NIR range are characterised and certified with this measuring system. Furthermore, errors in the optical structure of resonators of beam imaging systems can easily be analysed.

This PRIMES innovation directly measures the power density distribution of a focal geometry that was created by integrated focusing optics. That makes this system unique in the market.

Advantage of this measurement method: Disturbances from diffraction structures, misalignment, asymmetries and other effects become directly visible in the measured power density distributions.

Compact, simple, individually expandable

The LQM characterises the parameters of a beam source automatically and quickly in conformity with ISO standard 11146. This is a compact and easy-to-align measuring system which is positioned directly in front of the laser to be measured and is aimed at the laser beam. The LQM essentially consists of a basic system in which all optical components and measurement functions are completely integrated. The base device can be supplemented by front-end modules with beam splitters, absorbers and alignment units and its power potential increased into the multi-kilowatt range. Fibre holders, collimators, neutral density glass filter inserts and additional measurement optics are available if needed. Furthermore, integrated measuring stations can be supplied as custom solutions.


Measurement methods – the principle

The characterisation of a collimated laser beam with Rayleigh lengths that are typically ten metres requires a significant measurement effort due to the very long measurement ranges of three to six Rayleigh lengths. This form of measurement is normally impossible for reasons of space. For this reason ISO 11146 recommends, in the alternative, the measurement of a caustic generated by focusing in order to determine the diffraction index M².

The LQM generates this device-internal caustic by focusing the irradiated collimated laser beam. The focussed beam is displayed enlarged on the CCD chip via several integrated attenuators and a lens. From the two-dimensional power density distribution measured in this way, the LaserDiagnoseSoftware determines the radius, position and orientation of the beam. Through the procedures of this measurement system, and repetition of the measurement at various positions in the device, all parameters necessary for the description of the artificial caustic are determined. The electronic exposure time control of the CCD chip expands the dynamic range of the system. This means that in general it is not necessary to alter the filters during a measurement.

Due to the laser beam being thus focused and characterised, the measurement can be shortened from several metres to a few millimetres. The M² value can be easily determined in this fashion, since it is ensured that the optics used for focusing do not generate imaging errors which influence the beam to be measured. The values of the beam parameters of the focused laser beam are calculated back to the values of the collimated beam in accordance with ISO 11146.

Measured beam parametersBeam waist diameter / beam dimensions

  • Waist position / focal position with reference to the beam entry into the LQM

  • Beam radius

  • Far field divergence

  • Rayleigh length

  • Divergence

  • Beam propagation factor k

  • Diffraction index M²