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SCANpedia - welcome to the SCANLAB GmbH encyclopedia.

Here you'll find explanations and definitions of key technical terms from the fields of optics, scanner technology, laser technology and laser processing.

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Rayleigh length

The distance to the beam waist, until the beam diameter is increased by a factor of √2.

Unit: mm

M2 = Beam quality (laser-dependent)
k = Correction factor, depends on A and D (ideally 1.27; more typically between 1.5 and 2.0)
A = Aperture of the scan system
D = Beam diameter prior to focusing (typically 6 – 70 mm)
λ = Wavelength (typically 193 nm – 10.6 μm)
f = Focal length (typically 30 mm – 2,000 mm)


Repeatability describes the precision of multiple moves to the same point within a short time period (from a few milliseconds up to five minutes).

During repeated moves to a position within a short time period (from a few milliseconds up to five minutes), deviations will occur between the repetitions. For a warmed-up system (warm-up: 30 minutes) with steady ambient temperature and operational conditions, the imprecision's standard deviation (RMS ) lies within the specified range. Here, it is assumed that dither averages out.

Systems with digital encoders have clearly superior repeatability .


The Root Mean Square is identical to the standard deviation sigma if it fluctuates around 0. Here it is used synonymous with sigma.

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