How to choose the optimal laser characteristics for your material processing application?
A Quick Reference and Examples
An understanding of the relation between the material properties and the laser characteristics is essential to choose the optimal laser system. The laser-matter interaction is established by the material absorption and its thermodynamic properties. This absorption is highly dependant on the wavelength of the laser used.
To obtain an efficient laser process you need to choose a wavelength that is strongly absorbed by the material.
Pulsed lasers provide a better heating rate and a reduced heat-affected zone.
The laser process efficiency can be defined by the balance between the quality of the mark, the marking time and the cost of the laser system. All these elements play a role in the choice of the best laser processing solution.
Metals
Metals are heat resistant materials, engraving metals requires laser irradiation that creates a high density of energy. Basically, the average laser power leads to the melting of the metal and the peak power causes its evaporation.
Although metals reflect a high portion of the irradiated light, they can still be processed with high power continuous wave (CW) lasers or high peak power pulsed lasers like those used by Laserax. We chose to use a fiber laser emitting a wavelength around 1 μm. Lasers with a longer wavelength, like CO2 lasers (at 10.6 μm) have an even higher reflectivity approaching 99%. Nevertheless, they are still the most used laser for cutting metal plates. The fact is that the reflectivity of the metal decrease when its temperature increase, thus enabling the laser cutting, welding and marking process.
Plastics
Every plastic has different material properties when choosing a laser the light absorption spectrum is our main concern. The laser irradiation can generate direct chemical modifications, melting and evaporation of the material. Plastics are rarely seen in their pure state because several additives are used. Whether they are used to change its color, to improve ultraviolet (UV) resistance, to improve its moldability, to better its flame resistance or what have you all additives impacts laser marking parameters.
CO2 lasers are effective tools for engraving or removal plastics.
CW and pulsed fiber lasers are used to weld and mark plastics.
UV lasers give high-resolution patterning and material removal efficiency in microelectronics applications.
Organic materials
The marking of organic materials like wood is based on material carbonization which produces darkening of the surface and marks with high contrast. The mid-infrared wavelength of CO2 lasers has good absorption and makes it a very good choice to work on organic materials. Other mid-infrared wavelengths like 2.94 μm are also very interesting for processing organic materials. This wavelength can be obtained with specialty fiber laser sources based on fluoride glass fibers.
Glass
Glass is a brittle material and heating it with a laser generally creates thermomechanical effects carrying out microcracks. The characters marked in transparent glass are visible thanks to the light scattered by these micro-fractures in the heat affected zones. CO2 lasers marking system can be used to permanently mark glass.
In terms of cutting, glass is a very difficult material to cut with a laser. However, it is feasible to cut thin glass like gorilla glass phone screen with ultra-short laser pulses.
Ceramics
General properties of ceramics are a high melting temperature and high hardness. These materials are another class of materials which are rarely seen in their pure state, impurities are usually added. Most ceramics can be laser marked. they are, like glasses, difficult to cut because they tend to explode.