Metal cutting and other critical laser operations are sensitive to any variation in kerf width or cross-section. The kerf™s quality depends on the polarization orientation relative to the cut direction. This is illustrated in Figure 1.
Current theory suggests that the assumption of a focused beam striking the work piece at normal incidence is only true at the cut™s beginning. Once the kerf forms, the beam encounters metal at some large angle of incidence, Î˜, as shown in Figure 2. Light which is s-polarized with reference to such a surface is reflected much more than light which is p-polarized, leading to the difference in cut quality.
Introducing a quarter-wave (90°) reflective phase retarder into the beam delivery path eliminates kerf variations by converting linear polarization to circular polarization. Circular polarization consists of equal amounts of s-polarization and p-polarization for any beam orientation, therefore all axes encounter the same composition of polarization, and material is removed uniformly regardless of cut direction. This is illustrated in the photos below.
A linearly polarized beam is oriented so that the plane of polarization is 45° to the plane of incidence and strikes the RPR at 45° to the normal, as shown in Figure 3. The reflected beam is circularly polarized.
The substrate choice depends upon the power level at which the laser operates. Alternate substrates, including water-cooled copper, are available. Eighth-wave and sixteenth-wave RPR designs, and designs for peak wavelengths other than 10.6µm are also available. Please contact a II-VI sales representative to obtain a quotation.