This feature is attractive to designers, because once a prism has been constructed, it will retain orientational parameters that do not deviate and require no further adjustment in the final assembly, except for positioning the prism unit itself.
Prisms can also serve an identical function, except that the reflecting internal surfaces of prisms behave as rigidly mounted mirrors with each face having a permanent orientation with respect to all others. Mirrors are commonly utilized to fold the light beam through an optical system. These prisms are employed to produce polarized light for optical instruments such as microscopes and polarimeters. In contrast, polarizing prisms are birefringent crystals that divide incident non-polarized light into separate components polarized orthogonally to each other. The former are useful for redirecting light beams by total internal reflection while the latter can be employed to bend and separate light into its component colors. Prisms can be roughly divided into three general categories: reflecting prisms, polarizing prisms, and refracting or dispersion prisms. Thus, the binocular observation tube utilizes both prism and beamsplitter technology to direct beams of light having equal intensity into the eyepieces. In order to divert light collected by the objective into both eyepieces, it is first divided by a beamsplitter and then channeled through reflecting prisms into parallel cylindrical optical light pipes. Illustrated in Figure 1 is a diagram of a typical binocular microscope observation tube configuration. Both of these important optical tools are critical for laser applications that require tight control of beam direction to precise tolerances with a minimum of light loss due to scatter or unwanted reflections. In addition to being able to divide a beam of light into two components, a beamsplitter can also be utilized to combine two light beams or separate images into one.īeamsplitters and prisms are not only found in a wide variety of common optical instruments, such as cameras, binoculars, microscopes, telescopes, periscopes, range finders, and surveying equipment, but also in many sophisticated scientific instruments including interferometers, spectrophotometers, and fluorimeters. The remainder passes through the cube undeviated. When incorporated into an optical system, a portion of the light passing through the cube is deflected at a 90-degree angle upon encountering the mirrored interface between the wedge prisms. The most common beamsplitter design enlists two right-angle prisms that are coated on the hypotenuse to produce a semi-reflective surface, and then cemented together to form a cube. Beamsplitters can be as simple as a square or rectangular sheet of glass coated with reflective material or they can be integrated as surface coatings into complex multi-element optical assemblies. As the name implies, beamsplitters are utilized to redirect a portion of a light beam while allowing the remainder to continue on a straight path.
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