An understanding of the laser characteristics and the material properties is essential to making the best choice. At first glance, the most obvious distinction between lasers is the colour, with red, green and blue covering the majority of applications.

The key to successfully marking a material is the absorption rate of the material surface and the power of the laser. The material surface structure has to react to the laser light in order to create a mark or remove material, if the laser bounces off a reflective surface, it won’t mark and in the case of transparent or translucent materials, a laser can pass straight through. Once a suitable laser has been selected, the depth of mark is dependent on the material integrity and the power of the laser. Lasers are used to mark items as varied as inorganics such as steel and safety glass to wood and even fresh fish.

The difference in colour is due to the wavelength of the light emitted, with red lasers, mainly operating in the near infra red (NIR) at 1064nm (nanometres), being the most common due to the large range of materials that can be marked. Red lasers are typically cheaper and offer higher power ranges. However, there are exceptions; ferrous and non-ferrous metals generally have excellent absorption at 1064nm, while some precious metals react well to green light at a wavelength of 532nm, both red and blue tend to pass through, or bounce off glass and so green is a suitable choice there.

It is important to understand how the material to be marked absorbs laser light at the wavelength of the laser chosen. Many plastics, for example, absorb the higher wavelength laser output well and today many plastics are designed with additives included to make them sensitive to specific laser wavelengths. For example, tags used to identify livestock use this technology to provide a permanent, clearly visible identification of each animal.

Similarly, many of the buttons used in modern cars require a coloured back light to illuminate the text or icon. To achieve the detailed resolution and the huge numbers required, manufacturers use lasers to remove a defined layer from the surface of the switch to leave a coloured layer exposed in the required design. Due to the precise nature of the laser application, the switch can be produced accurately and efficiently while the ease of control allows different text or icons to be applied without impacting on production rates.

For more specialist applications green lasers, which operate at 532nm, are used. Where etching is required in glass, for example, a red laser would not be suitable as the structure does not react to this wavelength. Similarly, safety glasses designed to protect against red lasers can only be etched by green lasers.

Blue or ultra violet lasers, which produce wavelengths around the 260-400nm region, are used in more specialised areas. These are less common due to higher complexity and cost and tend to have lower outputs than red and green lasers. The technology used to produce each of these lasers varies considerably and so does the cost. Red lasers use a diode, optics, and some electronics, which makes these fairly easy to make and assemble, so red lasers are generally cheaper.

The green laser, on the other hand requires, in addition to the same components as a red laser, a frequency-doubling crystal and some special optics.  These have to be very carefully aligned in order for the laser to function properly. Because it takes lots of work to make a green laser, and due to a reduced demand for green lasers, their cost typically is higher than for a red laser.

 

The marking of organic materials such as wood, paper and leather can be achieved using a CO2 laser, which produces mid to far infrared light at 10.6um and can be used for labelling food packaging as well as some plastics and glass products.  The advantages of the CO2 laser are its simplicity and low cost with even quite high powers cheaply available.  However, the overall quality of the marks is not as high as that of other lasers previously described as the spot sizes and hence thicknesses of the lines marked are bigger.

Illuminar Technologies’ Predator desk-top laser system is available with a variety of precision red laser generators and heads, and other models are available with red, green or blue lasers, as well as combining vision systems which can mark items in random orientations. All Illuminar machines are supported by local application engineers and are suitable for marking, cutting, welding and texturing applications.