Features

• Fabricated from N-BK7
• Reflects an Inverted and Reversed Image 180°
• Choose from Three Prism Sizes
• Ø10 mm, L = 9 mm
• Ø25.4 mm, L = 22 mm
• Ø50 mm, L = 42 mm
• Four Coating Choices for Each Size
  • Uncoated
  • 350-700 nm (-A Coating)
  • 650-1050 nm (-B Coating)
  • 1050-1620 nm (-C Coating)

Thorlabs' retroreflectors, which are available both unmounted and mounted, are trihedral prisms manufactured from a solid piece of N-BK7 glass. Commonly referred to as corner cubes, these prisms are available unmounted or mounted in engraved SM-threaded lens tubes. Choose from three sizes (Ø10 mm, Ø25.4 mm, or Ø50 mm), each of which is available uncoated or with one of three antireflection coatings [350-700 nm (-A Coating), 650-1050 nm (-B Coating), or 1050-1620 nm (-C Coating)]. Coating curve information is shown in the Graphs tab.

Via three total internal reflections (TIR), an image or beam is reflected back towards its original direction. The beam or image will be reflected through 180° even if the angle of incidence is not zero. The insensitivity of the alignment of the prism makes it an ideal retroreflecting optic. For these retroreflecting prisms, the incident and reflected beams will be parallel to within 3 arcmin. However, unless the incident and reflected beams strike the exact center of the optic, they will not overlap but rather be shifted with respect to each other. For example, if the incident beam strikes the optic 3 mm to the right of center, the retroreflected beam will emerge 3 mm to the left of center. See the Polarization Output tab for more information.

Please refer to the Selection Guide tab above for assistance in selecting the appropriate prism for your application.

Click Here for Raw Data
Click to Enlarge

The transmission curve for N-BK7, a RoHS-compliant form of BK7, is shown to the right. The data was obtained for a 10 mm thick, uncoated sample and includes surface reflections. Each N-BK7 retroreflector prism can be ordered uncoated or with one of the following standard broadband AR coatings: 350-700 nm (Designated with -A), 650-1050 nm (Designated as -B), or 1050-1620 nm (Designated as -C).

These high-performance, multilayer AR coatings minimize surface reflections when used in the specified wavelength ranges. They are designed for angles of incidence between 0° and 30° (0.5 NA). The plot shown below indicates the performance of the standard coatings in this family as a function of wavelength for a single surface. Please note that broadband coatings have a typical absorption of 0.25% that is not shown in the reflectivity plots.

For optics intended to be used at larger angles, consider using a custom coating optimized for an angle of incidence of 45°; these coatings are effective from 25° to 52°.

Click to Enlarge

Thorlabs Lab Fact: Retroreflectors Alter Polarization State

We present laboratory measurements of the polarization state of a beam retroreflected through Thorlabs' PS971-A Retroreflector. In a polarization-dependent experiment, it's important to understand how the polarization of the input beam is altered during retroreflection. While input beams normal to the base strike each face of the retroreflector at a roughly 55° angle of incidence [1], the s and p polarization components experience different phase delays and are split differently, depending on the order of surfaces they reflect from. The base of the retroreflector (see image to the bottom right in the Overview tab) is imagined to be divided into sextants; a beam incident on any one sextant will be retroreflected through the sextant sharing the same vertical angle (see figure to the right). We find that the change in polarization is dependent upon initial polarization of the beam and input sextant.

For our experiment we used the HRS014 stabilized HeNe laser. The beam was retroreflected by a PS970-A Ø1" N-BK7 prism retroreflector (sold below) and propagated through a polarizer, after which its power was recorded. We measured beam power with the polarizer oriented horizontally, vertically, or at ±45°. Next, we inserted a quarter-wave plate into the beam path before the polarizer with the fast axis of the λ/4 wave plate aligned horizontally. The power of the beam was recorded with the polarizer set at ±45°. From this set of six measurements, the Stokes parameters were calculated, which yielded the parameters for the electric field polarization ellipse.

The two figures below summarize the measured results for the retroreflected polarization. The lower left figure shows the output beam by sextant for vertical input polarization; the lower right figure shows the output beam by sextant for horizontal input polarization. In both enlarged figures, A and B denote the major and minor axes respectively for the polarization ellipse. Θ is the angle between the major axis and the horizontal. Arrow heads mark the handedness of the polarization. Both Θ and handedness are reported as seen by an observer looking into the retroreflector. These measured results demonstrate that the polarization state of the retroreflected beam is dependent not only on the initial polarization of the incident beam, but also the sextant of the retroreflector that the beam in incident upon. For details on the experimental setup employed and the results summarized here, please click here.

Click for Additional Details

Click for Additional Details

Resources for the Interested Reader

The effects of retroreflectors on polarization state have been investigated via various methods: eigenpolarization states [2 - 4], internal incidence angles using transformations between internal reflections [5], and analytic geometry [1]. We present experimental results of polarization state changing through retroreflection and compare it to the theory developed in Ref. [1] though examination of the proper Jones and Rotation matrixes.

[1] J. Liu and R. M. A. Azzam, "Polarization properties of corner-cube retroreflectors: theory and experiment," Applied Optics 36, 1553-1559 (1997).
[2] E. R. Peck, "Polarization properties of corner reflectors and cavities," J. Opt. Soc. Am. 52, 253-257 (1962).
[3] P. Rabinowitz, S. F. Jacobs, T. Shultz, and G. Gould, "Cube-corner Fabry-Perot interferometer," J. Opt. Soc. Am. 52, 452-453 (1962).
[4] P.I Lamekin, "Intrinsic polarization states of corner reflectors," Sov. J. Opt. Tech. 54, 658-661 (1987).
[5] M. A. Acharekar, "Derivation of internal incidence angles and coordinate transformations between internal reflections for corner reflectors at normal incidence," Opt. Eng. 23, 669-674 (1984).

Selection Guide for Prisms

Thorlabs 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
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 and 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
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
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
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

Prism	Material	Deviation	Invert	Reverse or Rotate	Illustration	Applications
Beamsplitter Cube and Mounted Beamsplitter Cube	N-BK7 - Grade A 400-700 nm 700-1100 nm 1100-1600 nm	50:50 splitting ratio, 0° and 90° s- and p- pol. within 10% of each other	No	No		Double prism configuration and dielectric coating provide 50:50 beamsplitting nearly independent of polarization. Non-polarizing beamsplitter over the specified wavelength range.
Polarizing Beamsplitter Cube and Mounted Polarizing Beamsplitter Cube	SF2 420-680 nm 620-1000 nm 900-1300 nm 1200-1600 nm	p-pol. - 0° s-pol. - 90°	No	No		Double prism configuration and dielectric coating transmit p-pol. light and reflect s-pol. light. For highest polarization use the transmitted beam.