Unmounted Retroreflector Prisms (Uncoated)

Features

• Wavelength Range: 350 - 2000 nm
• Fabricated from N-BK7
• Reflects an Inverted and Reversed Image 180°
• Choose from Three Prism Sizes
• Ø10.0 mm
• Ø25.4 mm
• Ø50.0 mm

These unmounted retroreflectors are trihedral prisms manufactured from a solid piece of N-BK7 glass and left uncoated. Commonly referred to as corner cubes, the prisms sold here are available in three different sizes (Ø10.0 mm, Ø25.4 mm, or Ø50.0 mm). To mount these retroreflectors, we suggest either our V-mounts or our fixed optical mounts, which use a nylon-tipped setscrew to secure the retroreflector, as shown in the photo on the bottom right. Each of these retroreflectors is also offered mounted in an SM-threaded lens tube for easy integration into an optical system. For other coating and mounting options, please see the retroreflector selection guide above.

Retroreflectors reflect an image or beam back toward its original direction via three total internal reflections (TIR). The beam or image will be inverted and 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 arcsec. 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. The prisms can be used to retroreflect beams as large as the maximum beam diameter listed on the Specs tab.

Additionally, the retroreflected beam will experience a change in its polarization state when propagated through a solid retroreflector. See the Lab Facts tab for more information.

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

The video above shows the beampath through a retroreflector.

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Ø1" Retroreflector Mounted onto an FMP1 Fixed Optic Mount

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Thorlabs Lab Fact: Retroreflectors Alter Polarization State

We present laboratory measurements of the polarization state of a beam retroreflected through a Thorlabs 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 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 former generation HRS015 stabilized HeNe laser (replaced by the HRS015B). The beam was retroreflected by a Ø1" N-BK7 prism retroreflector 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.

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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.

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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).