In this post we will try to shed some light on the question “What is the best type of laser to use?”
In an earlier post it was stated that “The wavelength or color of the laser light determines what material can be marked with it. 1064 nanometer light is the best choice for marking all metals and many plastics. 1064 nanometer light is produced by YAG, YVO4 and Fiber lasers. Over the last several years, fiber lasers have begun to dominate sales of 1064 nanometer lasers because size, efficiency, long life and durability. 10,600 nanometer light is produced by CO2 lasers and is the best choice for marking wood, many plastics and organic materials. Modern CO2 lasers also enjoy the benefits of size, efficiency, long life and durability.
The material being marked dictates the best type of laser to use. Although some materials work equally well with either type of laser, one type is generally vastly superior over the other type for a particular material. If you are marking metals, for example, there is no question that a 1064 nanometer fiber laser is the correct type of laser to use. If you are marking wood then there is no question that a 10,600 nanometer CO2 laser is the correct choice. There is no such thing as a laser that marks all materials well. IT DOES NOT EXIST.”
The statements above are generally accurate but the real answer can be a bit more complicated. Let me explain.
CO2 lasers are pretty much in a class of their own. Modern CO2 laser markers are of the sealed beam type and enjoy relatively long life with long periods between maintenance intervals. They are available with a broad selection of output powers and can be configured with beam expanders and focusing lenses that are appropriate for the application that they are performing. What they all have in common is that they have an output wavelength of 10,600 nm and are RF excited. If your application is marking wood or cutting cloth, you will no doubt use a CO2 laser.
If you are marking or engraving metal products, things can appear a bit more confusing. Although YAG, Fiber, Vanadate and DPSS laser systems can be made to output other wavelengths of light (532nm, 355nm and 256nm, for example), most metal marking will be performed using the fundamental output wavelength of 1064nm. There are many laser products on the market that produce 1064nm light and all of them claim to be the best thing since sliced bread. Laser sales people have a reputation of using “specsmanship” to sell their products rather than simple facts. Laser specs can be misleading and not even have much to do with the performance of the laser for a particular application. So, what are some of the differences in those products?
YAG lasers have been around for decades. YAGs fall into the category of Solid State Lasers. Solid state lasers use a crystal or laser rod as the medium that produces the laser light. That laser rod must be excited by some energy source which is usually a lamp or bank of laser diodes which direct their light into the laser rod. Throw in a couple of reflective mirrors, a Q switch, mode restricting apertures and a beam expander and, bingo, you have a YAG laser that should be capable of being used in a laser marking system. YAGs have the advantage of being a very mature technology but the disadvantages of being very inefficient and maintenance intensive. There are lots of things that can and do go wrong with them.
Other Solid State Laser types are Vanadate and DPSS. These tend to be a bit more energy efficient than YAGs and are advertised as having longer life and a lower maintenance requirement than YAGs. They do, in fact, still have a laser rod, mirrors, Q switch and other components that can, over time, be problematic and require service. These laser types tend to have shorter pulse widths and that can be an advantage or disadvantage, depending on the marking application. Short pulse width lasers are able to deliver small amounts of energy to a substrate in a very short period of time. They are great at surface ablation on certain sensitive materials that can’t tolerate heat or require very narrow line widths. Most metal marking applications work better with lasers that provide more energy per pulse. Although more energy per pulse generates more heat, it also allows for faster material removal.
Fiber lasers are not “Solid State” lasers in that they do not use a laser rod as the lasing medium. Instead, they use a doped fiber as the lasing medium (hence the name fiber laser….not to be confused with fiber optic coupled pump sources). Mirrors are replaced with reflective bragg gratings. Although fiber lasers have somewhat shorter pulse widths than most YAG lasers, they tend to be considerably longer than the pulse widths of Vanadate and DPSS lasers.
Fiber lasers can also be designed with variable pulse widths in order to achieve shorter pulse widths. When the pulse width in a fiber laser is made short, there must be a corresponding decrease in pulse energy in order to avoid damage. Fiber lasers have the advantages of very long life and no maintenance. Additionally, they are the most energy efficient of all of the laser types mentioned. Energy efficiency not only makes for less electricity consumption, it makes the cooling task much simpler.
The marking application dictates the best laser for it. All of the above mentioned laser types have strengths and weaknesses. None of them will work well for every application.