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Distance Measurements with Lasers

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Ask RP Photonics for advice concerning devices for distance measurements, such as interferometers.

German: Distanzmessung mit Lasern, Laser-Entfernungsmessung

Lasers can be used in various ways to measure distances or displacements without physical contact. In fact they allow for the most sensitive and precise length measurements, for extremely fast recordings (sometimes with a bandwidth of many megahertz), and for the largest measurement ranges, even though these qualities are usually not combined by a single technique. Depending on the specific demands, very different technical approaches can be appropriate. They find a wide range of applications, for example in architecture, inspection of fabrication halls, criminal scene investigation (CSI), and in the military.

Techniques for Distance Measurements

Some of the most important techniques used for laser distance meters are as follows:

Laser Radar

A laser radar is a device which uses one of the distance measurement techniques as described above, and scans the direction of the distance measurement in two dimensions. This allows the acquisition of an image, or more precisely a depth profile of some object, as required e.g. in robotics. For acquiring such depth profiles at a higher rate, there are sensor chips similar to CCDs (charge-coupled devices) with internal electronics to detect phase shifts, so that the distance for each pixel can be measured simultaneously. This allows for rapid three-dimensional imaging with very compact devices.

Compared with ultrasonic or radio and microwave frequency devices (radar), the main advantage of laser distance measurement techniques is that laser light has a much smaller wavelength, allowing one to send out a much more concentrated probe beam and thus to achieve a higher transverse spatial resolution. Another advantage that an optical bandpass filter makes it possible to very effectively remove noise influences at other optical frequencies.

Various Issues

As essentially all other measurement techniques using lasers, laser distance measurements can be affected by laser noise. Other noise-related issues can arise from detection noise, stray light, and speckle effects.

The targets can have very different reflection and scattering properties. Problems can arise for very low reflection or for specular reflections.

Note that range finding with lasers can raise serious laser safety issues, particularly when intense pulses from Q-switched lasers are used. The related hazards can be strongly reduced by applying eye-safe lasers.


[1]H. Kikuta et al., “Distance measurement by the wavelength shift of laser diode light”, Appl. Opt. 25 (17), 2976 (1986)
[2]G. Beheim and K. Fritsch, “Range finding using frequency-modulated laser diode”, Appl. Opt. 25 (9), 1439 (1986)
[3]T. Bosch et al., “The physical principles of wavelength-shift interferometric laser rangefinders”, J. Opt. 23, 117 (1992)
[4]C.-M. Wu et al., “Heterodyne interferometer with subatomic periodic nonlinearity”, Appl. Opt. 38 (19), 4089 (1999)
[5]M.-C. Amann et al., “Laser ranging: a critical review of usual techniques for distance measurement”, Opt. Eng. 40 (1), 10 (2001)
[6]S. Poujouly and B. Journet, “Laser range-finding by phase-shift measurement: moving toward smart systems”, K. G. Harding, J. W. V. Miller, and B. G. Batchlor, eds., Machine Vision and Three-Dimensional Imaging Systems for Inspection and Metrology, Proc. SPIE 4189, 152, SPIE (2001)
[7]T. R. Schibli et al., “Displacement metrology with sub-pm resolution in air based on a fs-comb wavelength synthesizer”, Opt. Express 14 (13), 5984 (2006)
[8]K. Joo et al., “Distance measurements by combined method based on a femtosecond pulse laser”, Opt. Express 16 (24), 19799 (2008)
[9]I. Coddington et al., “Rapid and precise absolute distance measurements at long range”, Nature Photon. 3, 351 (2009)
[10]G. Berkovic and E. Shafir, “Optical methods for distance and displacement measurements”, Adv. in Opt. and Photon. 4 (4), 441 (2012)

See also: triangulation, time-of-flight measurements, interferometers, phase shift method for distance measurements, laser safety, laser applications

Category: metrology

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