129
Revision 00 EN - 01/2021
HP-MSM-HB
35,0(6
Z-position
This value provides the position of the focus points in the z-position. As the compensation curve takes the
measurement points into consideration, the calculated z-position is not necessarily located at the position,
which has measured the smallest radius.
Focus radius
The focus radius is the smallest beam radius in the caustic. Generally, this value is similar to the smallest
value measured, but not necessarily.
Due to different reasons it may occur that the adaptation to the measurement values was not carried out.
This is the case if the compensation curve does not lie close to the measurement values. In this case the
parameters of the adapted compensation curve are to be discarded.
Rayleigh length
The Rayleigh length is a derived parameter and describes the distance in z-direction with regard to which the
beam radius has increased by the factor √2 (=1.41) and concerning which the beam area has increased by
the factor 2. The Rayleigh length increases with the focal length of the focusing optics and the beam quality.
The doubled Rayleigh length is an approximate point of reference, up to which material thickness (metal) a
procession is possible with the optic employed.
In order to make sure that the adapted values have a high significance, the measurement is to be carried out
in a z-range of at least ±2 Rayleigh lengths. As demanded in the ISO 11146 5 to 6 Rayleigh lengths would
be ideal. However, this demand is often confronted with the problem of quickly sinking power densities of the
laser beam which is to be measured. In case of a distance of 2 Rayleigh lengths from the focus the power
density has sunk to just a quarter.
In this case the caustic measurement consists of a compromise between the desired measurement range in
z-direction and the power density (signal-to-noise ratio) necessary for a perfect measurement.
Cyclic caustic measurements
When performing cyclic caustic measurements, it is useful to store settings for various display parameters in
a data file. This data is available anytime and can be reloaded for a new measurement. For a quick check of
the beam or when it is necessary to measure only part of the caustic.
Cyclic measurements are normally performed over a period of 2 to 3 minutes; by Ethernet communication
much quicker. For measurements after laser or system servicing, you should use more planes to achieve
greater accuracy in the results.
To start a measurement, saved caustic data is loaded from the settings file. This is done through the menu
item
File > Load Settings
. The data is loaded after entering the desired file name.
