| Circular polarization is a used to ensure even metal
cutting in different axes. Unfortunately most high power
lasers have a linearly polarized output. To convert
linear polarisation to circular polarisation a ¼ wave
phase retarding mirror is needed. Often these are known
as polarisers, ECQ mirrors, or 90 degree retarders.
Laser Beam Products stock a range of standard
reflective phase retarder mirrors both from copper and
silicon, as well as offering custom designs.
Spec for Phase Retarders:
| Reflectivity 10.6µm, 45° AOI |
98% |
min |
| Phase Shift 10.6um, 45° AOI |
90° |
+/- 3° |
| Copper or Silicon Substrate |
Both |
|
Accurate control of the phase shift value of the
coating is needed to ensure high quality circular
polarization for consistent laser cutting.
It is essential that mirrors before and after the
polarizing mirror do not affect the polarization of the
beam (i.e they have zero phase shift).
Gold coated mirrors are recommended for this purpose
having one of the lowest phase shifts known (< +/-1
degree), and as a simple metal layer coating are very
reliable. Using Gold mirrors can be used for "fault"
finding where polarization problems are suspected |
|
Tips for using Phase Retarders
The mirror needs to be accurately positioned at 45°
angle of incidence to the beam, so beam is turned
through 90°.
The mirror needs to be accurately positioned at 45° to
the plane of polarization.
As the most expensive mirror, location should be away
from the cutting area, often inside the laser cabinet.
The mirror diameter should be 2.5 or 3 times the beam
diameter.
|
