Plate beamsplitters are designed to be used at a 45° angle of incidence. Since they have a finite thickness (as much as 3 mm) the beam is slightly displaced as it passes through the plate.
The dielectric coatings on plate beamsplitters are extremely polarization sensitive, and, with the exception of the laser-line beamsplitters, should be used with random or circularly polarized light.
The second surface of the plate beamsplitter is antireflection coated to minimize ghost beams. If ghost beams must be completely eliminated, consider using a cube or pellicle beamsplitter.
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