LASER DESIGN
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Figure 4-2 i401 beam ellipticity
Heat removal
Heat generated by excited CO
2
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 i401 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, and then rotates the
polarization through 45 degrees as an aid in applications where a circular polarizer is used. 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/beam rotator assembly which rotates the beam 45 degrees before exiting through the
output aperture.
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.
Converting the laser polarization from linear to circularly polarized light gives uniform cut quality in both
axes. Circularly polarized light can be generated without significant power loss by using a circular
polarizer (also known as a cut quality enhancer or CQE) or a simple phase retarding mirror.
For the simplest and most cost-effective solution, a reflective phase retarder, laser polarization must be
rotated by 45°. Because most lasers have horizontally or vertically polarized outputs with the cutting or
welding substrate placed horizontally, this rotation of the polarization is usually done by mounting the
