Description of Fused Quartz Optical Prisms
1. Right-Angle Prism
A right-angle prism is commonly used to redirect the light path or deflect the image formed by an optical system by 90°. Depending on the orientation of the prism, the resulting image may appear laterally correct but vertically inverted. Right-angle prisms are also applied in image combination and beam displacement.
When light enters through one of the right-angle faces, it
undergoes total internal reflection at the hypotenuse surface
(interface with air) and exits through the other right-angle face,
resulting in a 90° deviation.
When light enters through the hypotenuse surface, it experiences
total internal reflection at both right-angle faces (interfaces
with air) and exits back through the hypotenuse after being
deviated by 180°.
2. Wedge Prism
When used individually, a wedge prism can deflect a normally incident light beam on its vertical surface by a certain angle. The deflection angle depends on the wedge angle—different wedge angles result in different beam deviations. When the beam remains stationary and the wedge prism is rotated, it can produce a circular scanning output of the beam.
A pair of wedge prisms can steer the beam to any position within a full-angle 4θd circle, where θd is the deviation angle of a single prism. This beam steering is achieved by independently rotating the two wedge prisms. It is commonly used in imaging applications to scan the beam to various positions, enabling precise beam control.
3. Pentaprism
A pentaprism reflects incoming light twice within the prism, changing its direction by exactly 90°. The image remains upright and retains its original handedness (no inversion or mirroring). Compared to a single-reflection right-angle prism, a pentaprism can precisely deflect the incoming beam by 90°, regardless of the prism's mounting orientation. This makes it more stable than a system composed of two mirrors, as it eliminates sensitivity to the angle of incoming light.
As a result, pentaprisms are commonly used in various optical observation and calibration instruments, such as theodolites, collimators, and rangefinders. In DSLR cameras, the viewfinder's reflex system also uses a pentaprism to redirect the optical path at a fixed angle.
4. Dove Prism
The Dove prism has unique optical properties. When light enters from the slanted face, the output beam maintains its original direction but forms an inverted image. If the prism is rotated by an angle θ, the resulting image rotates by 2θ. When light enters from the bottom surface of the prism, the beam is reflected back in the opposite direction, also producing an inverted image.
The Dove prism performs best when used with collimated (parallel) light. If the incoming beam is convergent, astigmatism may be introduced, which degrades image quality. Additionally, because total internal reflection occurs within the Dove prism, a phase difference arises between the s- and p-polarized components, which can affect the polarization state of the transmitted beam.
5. Hollow Roof Mirror Prism
The hollow roof mirror prism reflects light that enters from the slanted surfaces of the prism. Unlike flat mirrors, the reflected beam remains parallel to the incident beam but is laterally displaced, avoiding issues caused by beam interference.
The two angled surfaces of the right-angle prisms are fixed at a precise angle, making the setup much more convenient and accurate compared to manually aligning two separate mirrors to achieve parallel beam reversal.
