Encyclopedia … combined with a great Buyer's Guide!

VLib
Virtual
Library
Sponsorship opportunity: support this popular resource, which serves the whole photonics community, and get recognition!

Retroreflectors

Definition: optical devices which reflect light in a direction which is parallel to the incident beam

German: Retroreflektoren

Category: general optics

How to cite the article; suggest additional literature

Author:

Retroreflectors are optical devices which reflect light in a direction which is parallel to the incident beam – and this for some range of beam directions. This is profoundly different from reflections at ordinary mirrors, where a light beam is reflected back in itself only for normal incidence on the mirror surface; any tilt of the mirror will modify the direction of the reflected beam. For some retroreflectors, there is a parallel offset of the reflected beam, but the direction is always quite precisely opposite to that of the incoming beam, limited only by the accuracy of the device.

Different kinds of retroreflectors are available:

The reflectance of a retroreflector is usually substantially lower than that of a highly reflecting laser mirror. Nevertheless, the directionality of the reflection can create a substantially increased brightness of an illuminated object.

Depending on the type of retroreflector, there can be substantial changes of polarization direction, and image rotation can occur.

There are “spoiled” retroreflectors, intentionally made such that the direction of the reflected beam is somewhat modified.

There are also a kind of retroreflectors where the retroreflection principle works only in a plane; tilts of the reflector in one direction still lead to deviating directions of the reflected beam. This is the case, for example, for prisms with two instead of three reflections.

Applications of Retroreflectors

Retroreflectors are used where it is essential to maintain the direction of the reflected beam without precisely keeping the right orientation of the reflecting device. Some examples:

  • A few retroreflectors have been placed on the Moon, e.g. during the Apollo missions, and can be used for time-of-flight measurements of the distance between Earth and Moon (lunar laser ranging; see also the article on laser rangefinders). The retroreflector property is essential for increasing the amount of reflected light received in a large distance.
  • Similarly, various satellites are equipped with retroreflectors for facilitating laser tracking of the position.
  • Retroreflectors are used on some road signs and vehicles, e.g. bicycles, for better visibility under illumination with headlights of cars, for example. Here, exact retroreflection would not be helpful, because a road sign or a bicycle should be seen by the car's driver rather than the headlights, but some degree of directionality of an imperfect retroreflector improves the visibility.
  • There are barcode labels based on retroreflective materials, which can be scanned from large distances.
  • Interferometers and optical delay lines often utilize a retroreflector for avoiding overly critical alignment, which would be problematic particularly for moving parts.

Suppliers

The RP Photonics Buyer's Guide contains 15 suppliers for retroreflectors.

See also: corner cube prisms, laser rangefinders, reflectance
and other articles in the category general optics

How do you rate this article?

Click here to send us your feedback!

Your general impression: don't know poor satisfactory good excellent
Technical quality: don't know poor satisfactory good excellent
Usefulness: don't know poor satisfactory good excellent
Readability: don't know poor satisfactory good excellent
Comments:

Found any errors? Suggestions for improvements? Do you know a better web page on this topic?

Spam protection: (enter the value of 5 + 8 in this field!)

If you want a response, you may leave your e-mail address in the comments field, or directly send an e-mail.

If you enter any personal data, this implies that you agree with storing it; we will use it only for the purpose of improving our website and possibly giving you a response; see also our declaration of data privacy.

If you like our website, you may also want to get our newsletters!

If you like this article, share it with your friends and colleagues, e.g. via social media:

arrow