Specifications

Diamond™ GEM, G, & K, Integrator’s Guide
30
BEAM PROPAGATION
Optics Basics
It is not the intent here to have an exhaustive discussion of optics
theory and beam propagation. That information is readily available
in optics and laser text books. The following basic optics informa-
tion will be helpful when designing a beam delivery system.
Beam Diameter
The typical Coherent CO
2
laser beam is very close to an ideal Gaus-
sian beam profile where the peak intensity of the beam is at the
center. In Figure 13, the intensity profile cutting through a laser
beam is shown for the ideal case. For these beams, the beam diam-
eter is defined as the width of the beam where the intensity is 13.5%
of the peak intensity. Based on the mathematical description of the
beam profile, this is a good first approximation of beam diameter.
The practical information here is selecting the clear aperture of
optics that the laser beam must go through. In order to allow at least
99% of the laser beam though an aperture it should be at least 1.5
times the beam diameter at that point. In actual practice, the clear
aperture should be selected to be several millimeters larger so it is
easy to align the beam through the optic. The laser beam information
provided in the data sheets is based on measurements using specific
instruments designed to measure beam diameters.
Figure 13. Beam Profile
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Transverse Beam Axis
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Relative Intensity
Gaussian Beam Profile
13.5% of
peak intensity
Beam Diameter