Synrad p250, User Manual, Page: 34 / 106

LASER DESIGN PAGE | 34
The structure of the resonator and internal beam conditioning optics combine to produce a near
Gaussian mode quality (M
2
factor) of <1.2. (p250 only) Beam waist diameter is typically 6.7 mm at the
output aperture and full-angle divergence due to diffraction is approximately 2.5 milliradians (a 2.5 mrad
divergence means that beam diameter increases 2.5 mm over every one-meter distance traveled-p250
only). Beam ellipticity measures approximately <1.2 as it exits the resonator, it becomes closer to 1.0 in
the far field (or at the point of focus) as shown in the figure below.
Figure 4-2 p250 beam ellipticity.
Heat removal
Heat generated by excited CO2 molecules is transferred to the bore walls by diffusion. Collected heat is
transferred to the water in the cooling tubes by conduction of the electrodes and aluminum envelope.
The coolant path is directed through corrosion-resistant copper alloy tubing to regulate laser
temperature for maximum stability.
Beam conditioning
The p250 laser incorporates a novel beam conditioning system that first converts the beam to a circular
profile, cleans up the beam to remove side lobes and improve beam quality. To do this, the laser beam
exits the resonator and is turned back on itself through a front folding block that directs the beam into a
cylindrical lens located about 0.63 m (25 in) away from the resonator output. The cylindrical lens
converts the beam into a round beam which is then focused by a spherical focusing mirror through a
water-cooled aperture (to remove any side lobes) and then onto another spherical mirror that collimates
the beam. This beam then passes the shutter mechanism and through the rear folding mirror.
Polarization
Polarization is important in achieving the best cut quality from a laser and this is usually achieved with
linear polarization aligned with the cut direction; however, in most applications where two axes of cut
are required, linearly polarized light can lead to differences in cut quality depending on the orientation of
the polarization with respect to the cutting direction.