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Triangulation

Author: the photonics expert (RP)

Definition: a method for distance measurements

Categories: article belongs to category optical metrology optical metrology, article belongs to category methods methods

DOI: 10.61835/xhs   Cite the article: BibTex plain textHTML   Link to this page   LinkedIn

Triangulation is a method for distance measurements, often using a laser. It exploits the ability of a laser beam to propagate in a well-collimated form (i.e. with small beam divergence) over large distances. In a typical case, the laser beam illuminates a point the distance of which from the laser device is going to be measured; the laser is essentially used as a pointer. Diffuse or specular reflections from that point are monitored with a position-sensitive detector which is mounted in some distance from the laser beam, such that the laser source, the object and the detector form a triangle. Distance information is obtained from the recorded beam position on the detector.

A high detection speed enabled by some detectors (e.g. lateral effect photodiodes) makes it possible to monitor the position of a moving or vibrating part e.g. of some machinery. The accuracy obtained may typically be one-thousandth of the measured distance.

For diffuse reflections, the distance may be limited by the requirement to receive a sufficient amount of reflected optical power; with specular reflections, much larger distances can be measured, but some kind of angular alignment is required.

The principle of triangulation can also be realized with a laser beam the direction of which is rapidly scanned in two dimensions. In that way, one can acquire three-dimensional (3D) images of a scene.

Requirements on the Laser Source

Ideally, a laser source for triangulation has a high beam quality to illuminate a small spot over a large distance. A certain optical power level is also required, particular for targets with diffuse reflection. An eye-safe laser wavelength (e.g. in the 1.5-μm region) may be beneficial with respect to laser safety, although a visible laser pilot beam helps to ensure that the correct point is targeted. Red laser diodes with a power of a few milliwatts are frequently used in combination with some beam shaper. A helium–neon laser with diffraction-limited beam quality can also be used, but is more bulky and expensive.

More to Learn

Encyclopedia articles:

Bibliography

[1]R. G. Dorsch et al., “Laser triangulation: fundamental uncertainty in distance measurement”, Appl. Opt. 33 (7), 1306 (1994); https://doi.org/10.1364/AO.33.001306

(Suggest additional literature!)

Suppliers

The RP Photonics Buyer's Guide contains 20 suppliers for laser rangefinders. Among them:

LEDlas

laser rangefinders

Our cutting-edge range finder utilizes advanced dToF technology to deliver exceptional long-range performance, reaching distances of 2–20 kilometers. Designed with safety in mind, our product is completely eye-safe, making it ideal for a variety of applications.

TOPTICA Photonics

laser rangefinders

Laser rangefinders can be used to monitor or measure distances or object lengths. They can also provide positional locations over long distances, e.g. several kilometers, without physically touching the observed object. The laser range finders are regularly used in geodesy, sports, hunting or military. Usually, the distances are measured with accuracies of up to a millimeter, whereas the measured object can even be in motion. In addition, measurements on natural surfaces with low reflectivity are also possible.

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