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Laser Marking

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Definition: a group of methods for labeling materials with lasers

German: Laser-Markieren, Laser-Beschriften

Category: methods

How to cite the article; suggest additional literature

Laser marking is a method for labeling various kinds of objects using a laser. The principle of laser marking is that a laser beam somehow modifies the optical appearance of a surface that it hits. This can occur through a variety of mechanisms:

laser marking station

Figure 1: TruMark laser marking station. The photograph was kindly provided by TRUMPF Laser.

By scanning the laser beam (e.g. with two movable mirrors), it is possible to quickly write letters, symbols, bar codes, and other graphics, using a vector scan or a raster scan. Another method is to use a mask which is imaged on the workpiece (projection marking, mask marking). This method is simple and faster (applicable even with moving workpieces) but less flexible than scanning.

Laser marking has a huge variety of applications:

Compared with other marking technologies such as ink jet printing and mechanical marking, laser marking has a number of advantages, such as very high processing speeds, low operation cost (no use of consumables), constant high quality and durability of the results, avoiding contaminations, the ability to write very small features, and very high flexibility in automation.

Plastic materials, wood, cardboard, paper, leather and acrylic are often marked with relatively low-power CO2 lasers. For metallic surfaces, these lasers are less suitable due to the small absorption at their long wavelengths (around 10 μm); laser wavelengths e.g. in the 1-μm region, as can be obtained e.g. with lamp- or diode-pumped Nd:YAG lasers (typically Q-switched) or with fiber lasers, are more appropriate. Typical laser powers used for marking are of the order of 10 to 100 W. Shorter wavelengths such as 532 nm, such as obtained by frequency doubling of YAG lasers, can be advantageous, but such sources are not always economically competitive. For marking of metals like gold, which has too low absorption in the 1-μm spectral region, short laser wavelengths are essential.

Demands on Lasers for Marking

Lasers for marking applications must meet a number of demands. Some typical ones are:

Depending on the specific circumstances, different types of lasers can be most suitable for a marking application. For example, Q-switched vanadate lasers can be superior when high pulse repetition rates (> 100 kHz) are important. Fiber lasers, which are in that case actually master oscillator power amplifier (MOPA) systems, are very flexible in terms of pulse repetition rates and interruption of pulse trains, but often emit longer pulses with lower pulse energies and peak power. CO2 lasers can be superior in cases where their long wavelength is suitable and a high average power is needed.

See also: lasers, lamp-pumped lasers, fiber lasers, laser applications
and other articles in the category methods

In the RP Photonics Buyer's Guide, 46 suppliers for equipment for laser marking are listed.

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