PRIMES
BeamMonitor BM+ with LDS 2.98
45
Revision 01/2018 EN
11.2.5
Caustic display (2D-display)
The results of the caustic measurement can be displayed by means of the menu item
Presentation>>Caustic
.
On the left Fig. 11.14 shows the measured beam parameter either on the basis of the 86%-radii or the mo-
ment evaluation according to ISO 11146. In the middle of the picture the graphic shows the caustic profile.
The beam radii are depicted on the beam spread direction. On the right the false color presentation of one
measurement plane each – among other things selectable with the mouse - is shown together with numeri-
cal results of this single plane.
Fig. 11.14: Dialogue window
Presentation>>Caustic
The red line depicts a compensating curve according to the calculated fits which can be displayed via the
check box
Fit
in the 2D presentation
Compensating curve
In order to evaluate the caustic, a hyperbolic compensating curve (ISO 11146) is adapted to the measur-
ing values. This compensating curve describes the propagation of an ideal laser beam mathematically. The
development of the compensating curve is theoretically determined by means of the following parameters:
•
standardized beam propagation factor M² or respectively beam propagation ratio
•
z-position
•
focus radius
•
rayleigh length
Standardized beam propagation factor M² (or respectively the beam propagation ratio K= )
The standardized beam propagation ratio describes how well the respective laser beam can be focused in
relation to the single mode. The single mode is the best beam which is theoretically possible and has a beam
propagation factor of 1. All other beams have higher values. For welding lasers (CO
²
) the values range from
2 to 5. With regard to cutting lasers (CO
²
) values from 1.1 to 2.5 are common. In case of beam sources with
a higher laser power the beam propagation factors are generally smaller than those of sources with lower
laser powers.
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 beam
radius, which has measured the smallest position.
The device coordinates are given. Information with regard to the absolute position in space can be found in
chapter 23.2.4 on page 83. Possibly also on basis of a TCP calibration (option).
