L2-D

Beam Splitters
A beam splitter is a device that’s used to divide an optical beam into two or more components according to given criteria. Beam splitters can be grouped into the following four classifications. These classes include those beam splitters that divide the beam size according to beam intensity, wavelength, polarization, or physical size.
The most common beam splitter is a partially reflective mirror. This mirror allows a predetermined percentage of the light to be transmitted while reflecting the remaining portion. The actual percentage of the beam reflected and transmitted depends on the coatings applied during the manufacturing process. Coatings commonly available include inconel and achromatic dielectric. Beam splitters with these coatings can be made to give a transmitted to reflected beam ratio of 30% – 70%, 40% – 60% and 50% – 50%. Variable-density beam splitters wherein reflectivity of the coating is varied across the surface of the beam splitter are also available. The variable density beam splitter allows you to change the beam ratio by using different locations on the beam splitter.
Partially reflective beam splitters have serious limitations. They provide a high loss factor, multiple reflections and distortions. To understand these limitations see Figure 13. Multiple reflections cause both the reflected and transmitted output beams to look similar to the cross-sectional views shown in Figure 14 Areas where the beams overlap produce interference patterns when the incident light is monochromatic, coherent laser light. If the light is not monochromatic, coherent light, ghost images can be produced.