Laser beams often have to be split into two or more partial beams – and sometimes even yield different power levels! The following options are available:
Classic beam splitters are produced for a single wavelength and a specified polarization. A partially reflecting dielectric coating is applied to a coplanar plate. The wavelength and polarization are determined by the customer. For example, a reflection of 50% can be achieved for s-pol light at 1064 nm. The remaining light is then transmitted. If the beam splitter described above is used with p-pol light, then the degree of reflection is completely different (i.e., in this case, approximately 30%).
For predictable results, the customer must make sure that the polarization of the laser is fixed and does not change during operation.
Polarization-independent beam splitters. These beam splitters are used if the same reflection is intended for both polarization states. The coating is applied to the substrate using the ion beam sputtering (IBS) technique. This time-consuming and thus expensive method is the only way to ensure deviations of less than 1% between p- and s-polarized light.
Variable beam splitters are required to achieve identical intensities at several operating stations (e.g., in laser material processing). These beam splitters have an “area of adjustment” of 45% to 55%: Their reflectivity varies along the position of the substrate and can, therefore, be readjusted, allowing the correction of deviations in the beam path.
Different types of beam splitting cubes provide another way of splitting a laser beam into two partial beams. Diffractive optical elements can also be used in high-power lasers. The next issue will go into more depth on this subject.
