Measurement methods – the principle
The HighPower-MSM-HighBrilliance determines beam parameters of focused laser beams of multi-kilowatt lasers in the range of 20 micrometres up to a millimetre directly in the process zone – even at full power.
For this purpose, 95% of the laser power is transmitted by a beam splitter through the measurement optic, and absorbed. The remaining five per cent are further attenuated in the measurement optic and destroyed by internal water-cooled absorbers. A part beam with a few milliwatts of power is imaged on the CCD sensor in an enlargement.
The measurement optic was designed for beam powers up to ten kilowatt single-mode. The HighPower-MSM-HighBrilliance is also equipped with a safety circuit that can be connected with the laser and interrupts the laser emission in the event of overheating or device failure. In this way the measuring device is protected from damage.
The HighPower-MSM-HighBrilliance individually measures power density distributions in the focal area of up to 50 measurement planes. The focal caustic is composed of these power distributions. From each individual distribution beam, geometries such as beam position, beam radius and half-axis lengths and also the tilt of the half-axes to the device axis according to the procedure described in standard ISO 11146 (2nd moments and 86 % power inclusion) are determined.
The beam propagation parameters such as focal position, focal radius, Rayleigh length, divergence, diffraction index M² and beam parameter product are broken down from the beam geometry data. The ellipticity of the focus and the astigmatic difference are determined from the measurement data for the half-axes of the beam in accordance with ISO 11146.
Additionally the beam direction error can be determined from the fibre. Along with the caustics measurements described, the HighPower-MSM-HighBrilliance also allows examinations of the temporal behaviour of the power density distribution of a particular plane to be carried out.
At a temporal resolution of around 2 seconds, the behaviour of the laser in the workpiece plane can be observed, for example.