All prism faces are flat. Non-optical surfaces are left in their as-ground condition. Optically active faces are all ground and polished to the specified degree of flatness. As prisms are made from solid materials, the optical path within the prism is fairly long compared with other optical components. Prisms used in optical systems with a convergent or divergent beam introduce optical aberrations. When using prisms in imaging or focusing systems, it is important to have collimated or near-collimated beams in this portion of the system.
Dove prisms invert an image by 180 degrees. If the prism is rotated about its axis, the image rotates at twice the rate of the prism. Easy to mount, dove prisms provide a convenient and precise method of rotating a beam. These prisms have a broadband multilayer AR coating on the end faces. The hypotenuse face acts as a TIR surface and is normally uncoated.
Right Angle Prisms and Knife Edge Prisms
These versatile prisms work as internal or external reflectors or as retro-reflectors according to their orientation. Although uncoated prisms work well, their useful full field of view is limited to 10 or 12 degrees in the visible. Broadband Multilayer AR coatings withstand high power laser use, while Protected Aluminium coatings have a layer of MgF2 to protect against scratches and abrasions.
Penta prisms deviate an input beam by 270 degrees, independent of the angle of incidence on the first surface. They are useful as alignment insensitive, precise right angle mirrors. These penta prisms are AR coated on the entrance and exit faces, and coated with protected aluminium and black paint on the internal reflection faces.
Retro-Reflectors and Hollow Retro-Reflectors
Retro-reflectors, or corner cubes, reflect light incident on the surface back along the same path. These precise retro-reflectors provide an exact 180 degree deviation within a 2arcsec tolerance. They are suitable for high precision applications and with lasers over long distances. A broadband AR coating on the face is standard. Optional black paint protected silver may be specified for the legs. Hollow retro-reflectors keep the entire optical path in air. As a result, they work as broadband reflectors. The design also reduces the effects of polarisation and chromatic aberration. These "angle insensitive" mirrors have numerous uses in alignment and metrology.
Precision Wedge Prisms
These wedge prisms are for steering laser beams. By selecting the appropriate wedge prism, you can accurately steer a beam without affecting other beam parameters. These grade A optical glass wedge prisms are offered uncoated or with optional AR coatings.
Equilateral prisms are normally used for the dispersion of light into its different colours. Light incident at an oblique angle to the first face is dispersed according to its wavelength and emerges as a spectrum from the opposite face.