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Encyclopedia of Laser Physics and Technology

Laser Marking

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Definition: a group of methods for labelling materials with lasers

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 it hits. This can occur through a variety of mechanisms:

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 (it can be applied 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 or 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, 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 W 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.

Demands on Lasers for Marking

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

Depending on the concrete 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

Category: methods

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