What is a plate or "mirror-type" beamsplitter?

A beamsplitter is an optical component that divides light (i.e., a beam) into two separate portions (beams). When the component is inserted into an optical path at a specific angle (typically 45°), a portion of the beam will be diverted (reflected) in a different direction (typically 90° from the input beam). A beamsplitter will reflect a portion of the incident energy, absorb a relatively small portion, and transmit the remaining energy. It is essentially an optical window (clear glass or film) that has a metallic or dielectric coating on one side with specific reflecting and transmitting characteristics. A plate beamsplitter is the most common type and has a thin glass substrate. They are also known as "mirror-type" beamsplitters due to the reflective nature of the coatings used. We offer plate beamsplitters with the most common reflection percentages (30%, 50%, and 70%), as well as a variety of others. The reflective coating is optimized at 45°. An anti-reflection coating is available on the back surface of many of the beamsplitters and it is also optimized at 45°. The spectral curves shown with the product are for the average of the S- and P-states of polarization. It should be noted that these types of beamsplitters are very sensitive to polarized light.