PRIMES
BeamMonitor BM+ with LDS 2.98
83
Revision 01/2018 EN
23.2.4
Radius determination with the method of the 86 % power inclusion
The first step is the determination of the volume of the power density distribution. It is proportional to the
total power. The addition of all power density values and their multiplication with the pixel dimensions result
in the volume and therefore the total power. A reliable zero level subtraction is the fundamental basis.
Based on this total power, the focus lies on the range which includes the 86 % of the total beam power. This
beam power must lie within the beam radius.
The integration typically starts with the values of the maximum power density. Then the integration range is
enlarged until 86 % of the total power lie within the radius. As far as the integration is concerned, the number
of pixels is counted. By means of this the 86 % range which means the beam diameter can be determined.
For circular beams similar to the fundamental mode beams the procedure works well.
Fig. 23.4: Graphical presentation of the calculation of the 86% radius
a) shows the power density distribution
b) shows the pixels which include 86 % of the power together. As a clarification the pixels with a low power
are set to zero.
c) shows a section at the “86 % power density inclusion”. The level lies at 14 % of the maximum power
d) shows the section through the distribution at 86 %.
