Round Wedge Prisms
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Thorlabs' Wedge Prisms are ideal for laser beam steering applications. Also known as Risley prisms, these optics deflect a beam normal to the prism's perpendicular surface through an angular deviation ranging from 2° to 10°. Please refer to the Specs tab for the angular deviation of each wedge prism. For your convenience, Thorlabs' wedge prisms can be purchased uncoated or coated with one of three standard broadband AR coatings. Wedge prisms can be used individually or in combination with another wedge prism for beam steering. For more details, and to see a sample application, click on the Application Idea tab above. 
Click to Enlarge
The drawing above depicts a single wedge prism and an incident beam of light. The incident light is refracted at the specified deviation angle. As the wedge is rotated, the deviated beam traces out a circle defined by an angle equal to two times the specified deviation angle. 
Click to Enlarge
The drawing above depicts two wedge prisms and an incident beam of light. Since each individual prism can trace out a circle of two times the deviation angle, the total deviation by two prisms will be four times the deviation angle. By controlling the angle of each prism independently, the beam can be positioned at any point within the circle. |
Specifications- Material: N-BK7, Grade A
- Dimensional Tolerance: ±0.15 mm
- Diameter: 25.4 mm +0.0/-0.3 mm
- Angular Tolerance: ±30 arcsec
- Surface Quality: 40-20 Scratch-Dig
- Surface Flatness: λ/10 at 633 nm
- Design Wavelength: 633 nm
- Thin Edge of Wedge: 3.00 mm
- Broadband Antireflection (AR) Coatings: 350 - 700 nm, 650 - 1050 nm, and 1050 - 1620 nm
| Item # | Angular
Deviation | Thickness (T)
(mm) | Wedge
Angle | Powera
(Diopter) |
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| PS810 | 2o | 4.72 | 3o 53' | 3.5 | | PS811 | 4o | 6.43 | 7o 41' | 7.0 | | PS812 | 6o | 8.11 | 11o 22' | 10.5 | | PS814 | 10o | 11.33 | 18o 9' | 17.4 |
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Application Ideas
Introduction and Setup
Wedged prisms are designed to be used, either individually or in a pair, for beam steering applications. This is done by individually controlling the rotation of each prism using our PRM1Z8motorized rotation stages. The list of components for the configuration pictured to the right is in the following tables; clicking on the item number will bring up a pop-up window with more information about that component. | Item # | Quantity | Description |
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| PS814-A | 2 | Wedge Prism with 10° Wedge Angle | | PRM1Z8 | 2 | Motorized Rotation Mount | | TDC001 | 2 | T-Cube Controller | | TPS001 | 2 | T-Cube Power Supply | | LDM635 | 1 | 635 nm Laser Diode Module | | KM200V | 1 | Kinematic V-Groove Mount | | TR3 | 3 | Ø1/2" Post, 3" Long | | PH3 | 3 | Ø1/2" Post Holder, 3" Long | | BA2 | 1 | Post Holder Base | | BA1 | 1 | Post Holder Base |
Tracing a Circle with One Prism
For this application, one of the two rotation mount-prism assemblies was removed from the setup. The remaining rotation mount was activated, so that the deviated beam will rotate as well to remain aligned with the wedge. The result of a full rotation of the prism is shown to the right in a long-exposure photograph. This circle is defined by the cone equal to two times the deviation angle (since the deviation angle of the prism used was 10°, the total angle was 20°).
Tracing a Circle with Two Prisms
For this application, The rotation mounts are set so that the wedges of both prisms are aligned. Since each prism will deviate the beam by the deviation angle, The total beam deviation for two prisms with the wedges aligned will be 2 times the deviation angle of one prism. If both prisms are rotated at the same rate and in the same direction, the beam will trace out a circle which is twice the size of the circle traced out by a single prism. The circle is defined by the cone equal to four times the deviation angle of a single prism (since the deviation angle of the prisms used was 10°, the total angle was 40°). The long-exposure photograph to the right was taken with the prism assembly at the same distance from the screen as the one-prism circle above. Notice that the circle in the two-prism case is about twice the diameter of the one formed with one prism.
Tracing a Spiral
If the rotation of the two prisms is controlled individually, the prisms can be set so that the wedges are opposite to one another. Thus, the beam deviations from each individual prism will cancel, and the beam will appear on the screen undeviated. In much the same way, by appropriately setting the wedge angle of each prism, the beam may be deviated to any position within the circle defined by the cone equal to four times the deviation angle of a single prism. As an example, the long-exposure photograph to the right shows two wedged prisms being used to trace out a spiral. This was realized by first setting the beam to be undeviated, and then having the prisms rotate in the same direction, with one prism set to rotate 0.5 °/s faster than the other.
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Selection Guide for PrismsThorlabs offers a wide variety of prisms, which can be used to reflect, invert, rotate, disperse, steer, and collimate light. Prisms are available in N-BK7, UV Fused Silica, F2, N-SF11, α-BBO, N-KZFS8, Ge, and CaF2. For prisms and substrates not listed below, please contact tech support. Beam Steering Prisms| Prism | Material | Deviation | Invert | Reverse or Rotate | Illustration | Applications |
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| Right Angle Prisms | N-BK7, UV Fused Silica, Germanium, or Calcium Fluoride | 90° | 90° | No |  | 90° reflector, independent of entrance beam angle. Used in optical systems such as telescopes and periscopes. | | 180° | 180° | No |  | 180° reflector, independent of entrance beam angle. Acts as a non-reversing mirror and can be used in binocular configurations. | Retroreflectors
and
Mounted Retroreflectors | N-BK7 | 180° | 180° | No |  | 180° reflector, independent of entrance beam angle. Beam alignment and beam delivery. Substitute for mirror in applications where orientation is difficult to control. | Penta Prisms
and
Mounted Penta Prisms | N-BK7 | 90° | No | No |  | 90° reflector, without inversion or reversal of the beam profile. Can be used for alignment and optical tooling. | | Roof Prisms | N-BK7 | 90° | 90° | 180o Rotation |  | 90° reflector, inverted and rotated (deflected left to right and top to bottom). Can be used for alignment and optical tooling. | Dove Prisms
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Mounted Dove Prisms | N-BK7 | No | 180° | 2x Prism Rotation |  | Dove prisms may invert, reverse, or rotate an image based on which face the light is incident on. Prism in a beam rotator orientation. | | 180° | 180° | No |  | Prism acts as a non-reversing mirror. Same properties as a retro-reflector or right angle (180° orientation) prism in an optical setup. | | Wedge Prisms | N-BK7 | Models Available from 2° to 10° | No | No |  | Beam steering applications. By rotating one wedged prism, light can be steered to trace the circle defined by 2 times the specified deviation angle. | | No | No |  | Variable beam steering applications. When both wedges are rotated, the beam can be moved anywhere within the circle defined by 4 times the specified deviation angle. | | Coupling Prisms | Rutile (TiO2) or GGG | Variable* | No | No |  | High index of refraction substrate used to couple light into films. Rutile used for nfilm > 1.8 GGG used for nfilm < 1.8 |
* Depends on angle of incidence and index of refraction
Dispersive Prisms
| Prism | Material | Deviation | Invert | Reverse or Rotate | Illustration | Applications |
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| Equilateral Prisms | F2, N-SF11, Germanium, or Calcium Flouride | Variable* | No | No |  | Dispersion prisms are a substitute for diffraction gratings. Use to separate white light into visible spectrum. | | Pellin Broca Prisms | N-BK7, UV Fused Silica, or CaF2 | 90° | 90° | No |  | Ideal for wavelength separation of a beam of light, output at 90°. Used to separate harmonics of a laser or compensate for group velocity dispersion. | | Dispersion Compensating Prism Pairs | Fused Silica, CaF2, SF10, or N-SF14 | Variable Vertical Offset | No | No |  | Compensate for pulse broadening effects in ultrafast laser systems. Can be used as an optical filter, for wavelength tuning, or dispersion compensation. |
* Depends on angle of incidence and index of refraction Beam Manipulating Prisms| Prism | Material | Deviation | Invert | Reverse or Rotate | Illustration | Applications |
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| Anamorphic Prism Pairs | N-KZFS8 or N-SF11 | Variable Vertical Offset | No | No |  | Variable magnification along one axis. Collimating elliptical beams (e.g., laser diodes) Converts an elliptical beam into a circular beam by magnifying or contracting the input beam in one axis. |
Polarization Altering Prisms| Prism | Material | Deviation | Invert | Reverse or Rotate | Illustration | Applications |
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| Glan-Taylor, Glan-Laser, and α-BBO Glan-Laser Polarizers | Glan-Taylor:
Calcite Glan-Laser:
α-BBO or Calcite | p-pol. - 0° s-pol. - 112°* | No | No |  | Double prism configuration and birefringent calcite produce extremely pure linearly polarized light. Total Internal Reflection of s-pol. at the gap between the prism while p-pol. is transmitted. | | Rutile Polarizers | Rutile (TiO2) | s-pol. - 0° p-pol. absorbed by housing | No | No |  | Double prism configuration and birefringent rutile (TiO2) produce extremely pure linearly polarized light. Total Internal Reflection of p-pol. at the gap between the prisms while s-pol. is transmitted. | | Double Glan-Taylor Polarizers | Calcite | p-pol. - 0° s-pol. absorbed by housing | No | No |  | Triple prism configuration and birefringent calcite produce maximum polarized field over a large half angle. Total Internal Reflection of s-pol. at the gap between the prism while p-pol. is transmitted. | | Glan Thompson Polarizers | Calcite | p-pol. - 0° s-pol. absorbed by housing | No | No |  | Double prism configuration and birefringent calcite produce a polarizer with the widest field of view while maintaining a high extinction ratio. Total Internal Reflection of s-pol. at the gap between the prism while p-pol. is transmitted. | Wollaston Prisms
Wollaston Polarizers | Calcite | Symmetric
p-pol. and
s-pol. deviation angle | No | No |  | Double prism configuration and birefringent calcite produce the widest deviation angle of beam displacing polarizers. s-pol. and p-pol. deviate symmetrically from the prism. Wollaston prisms are used in spectrometers and polarization analyzers. | | Beam Displacing Prisms | Calcite | 2.7 or 4.0 mm Beam Displacement | No | No |  | Single prism configuration and birefringent calcite separate an input beam into two orthogonally polarized output beams. s-pol. and p-pol. are displaced by 2.7 or 4.0 mm. Beam displacing prisms can be used as polarizing beamsplitters where 90o separation is not possible. | | Fresnel Rhomb Retarders | N-BK7 | Linear to circularly polarization Vertical Offset | No | No |  | λ/4 Fresnel Rhomb Retarder turns a linear input into circularly polarized output. Uniform λ/4 retardance over a wider wavelength range compared to birefringent wave plates. | | Rotates linearly polarized light 90° | No | No |  | λ/2 Fresnel Rhomb Retarder rotates linearly polarized light 90°. Uniform λ/2 retardance over a wider wavelength range compared to birefringent wave plates. |
* s-polarized light is not pure and contains some p-polarized reflections. Beamsplitter Prisms
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Wedge Prisms
