To measure the polarization of high power laser
- Measuring tool for characterization of the degree and angle of polarization
Application
Polarization dependent effects during material processing with CO2- lasers are well known. An example for this is shown in figure 1: the dependence of welding depth as function of the welding velocity. Two curves are shown for p- and s- polarization (plane of polarization parallel (p) and perpendicular (s) to the plane of incidence). As can be seen, especially for high welding velocities (> 3 m/min) there is a considerable difference between the welding depths for s- and p- polarization.
Also in laser cutting processing results and processing velocity depend on the degree and the angle of polarization.
These phenomena lead to processing results which are strongly dependent on the processing direction.
So it has become common to use phase retarders, to avoid any dependence of system's performance on processing direction during cutting and welding. These phase retarders transfrom linear polarized radiation into circular polarized radiation.
Theoretically every dependence of processing direction due to polarization should be eliminated. But in practical application it is very difficult to check the real polarization degree of the beam.
Technical description
Polarization is measured by the rotating four special coated mirrors. Depending on the orientation of the polarization the mirrors absorb 99 % of one polarization direction and reflects 99 % of the perpendicular direction. With this assembly a high contrast for analyzing the polarization is obtained.The laser beam is attenuated by two beam splitters. The angle between the two beam splitters is selected in such a way to avoid a change of the polarization state of the transmitted beam. The transmitted power is only 25 ppm of the incoming beam.The laser power which is reflected by the mirrors is focused by a lens on the detector. During the rotation of the mirrors the measured power and the angle of the mirrors are recorded.
Technical data
- Dimensions (Height, Length, Width): 420 mm x 150 mm x 150 mm
- Apertur : 55 mm
- Power range : up to 2 kW
- Maximum Power Density : 2 kW/cm2
- Degree of Polarization :
±1 % absolut for the range of 0 % - 20 %
±2 % absolute for the range of 20 % - 40 %
±4 % absolute for the range of 40 % - 100%
- Direction of Polarization :
±2° for linear polarized beam
- Power supply : DC 24 V and 0,5 A
- Electrical connectors : 2 x PRIMES-RS485-bus (9-pin D-sub-min)
