Laser marking is a widely used method of permanent marking throughout many sectors, largely due to its accuracy and efficiency. Able to mark ultra-precise detailed inscriptions such as Data Matrix codes at a faster rate than other marking methods, laser engraving has become an essential part of product ID and traceability processes. When investing in laser marking equipment, it’s important to gauge which style of machine is most beneficial to you. We’ve put together this guide to the three major kinds of laser marking machines to give you an insight into the benefits and drawbacks of each.
Carbon Dioxide (CO2) Laser Marking
Carbon dioxide lasers consist of a gas filled discharge tube with a reflector at one end, with a partially reflecting mirror acting as an output coupler at the other. Electricity passes through this gas-filled tube, which produces light. This light is then reflected through the partially reflecting mirror to produce the laser.
How it Works
The mixture of gases within the discharge tube contains carbon dioxide, nitrogen, hydrogen and helium. When an electric current passes through the nitrogen molecules, the gas mixture becomes ‘excited’ (gaining energy). Nitrogen particles can hold this state and maintain their energy for long periods of time, without losing energy in the forms of light. This starts a chain reaction throughout the gas mixture, with the vibrations of the nitrogen particles exciting the CO2 particles. When this happens, the gas mixture has a higher number of energy-filled particles than non-energy-filled, which is referred to as population inversion.
Then, the nitrogen atoms come into contact with the cold helium atoms, which causes the nitrogen to emit light in the form of photons. These photons are then reflected by the mirrors within the chamber, which causes the intensity of the light to build as it travels back and forth through the tube. When the light becomes bright enough to pass through the partially-reflective mirror, the light is emitted as a laser beam.
The wavelength of a CO2 laser tends to be around 10,600 nanometres, making it a long wavelength that sits in the mid-infrared range. This means that the laser beam is invisible to the human eye, therefore it is often coupled with a neon laser pointer for navigation purposes.
Applications of CO2 Lasers
CO2 lasers are well suited for marking on materials such as plastic, ceramic, rubber and paper, but due to their high infrared wavelengths, they are not an ideal choice for marking on metal. This is because when infrared radiation hits the surface of a metal object, the electrons contained in the atoms of the metal match the speed of the radiation’s wavelength, causing the laser to reflect and not leave a mark.
YAG Laser Marking
YAG lasers, also called flash lamp or lamp-pumped lasers, operate at a lower wavelength than CO2 lasers. These lasers use a bulb lamp as a pumping mechanism and Yttrium Aluminium Garnet (YAG), which is a synthetic crystal, as the gain medium for the laser.
How it Works
A YAG laser consists of three main elements, the energy source, the active medium and the optical resonator. The energy source is a light source (the bulb lamp), which supplies energy to the YAG crystal (the active medium). The YAG crystal is doped with neodymium, which acts as the excitable particles for the YAG laser. When the light energy is applied to the YAG crystal, the neodymium ions become excited into a high energy state, which creates a state of population inversion, producing light. Similar to the CO2 laser, this light is bounced between two mirrors to increase the intensity until it is bright enough to pass the partially silvered mirror.
The laser generated by a YAG system typically sits in the near infrared region of the light spectrum, at around 1064 nanometres. This means that a YAG laser beam is also invisible to the human eye.
Applications of YAG Lasers
YAG lasers tend to be more popular for marking on metal, due to their lower wavelength. YAG lasers are not perfectly equipped for efficiency. The lamp bulbs of the laser diodes that are used often generate a lot of heat, which requires a liquid coolant to maintain. This means that heat and light energy is wasted via the bulbs, which also tend to have short lifespans when used consistently. For this reason, our final kind of laser has become the most popular type of laser marking technology in recent years.
Fibre Laser Marking
Solid state fibre lasers have become the industry standard for laser marking equipment, due to their overall quality and reliability. The term ‘solid state’ refers to the sealed laser source, which is protected against contaminants such as dust particles or the conditions of the environment in which it is used. This compact design also helps the fibre laser’s efficiency, stopping any light leakage and ensuring laser density.
How it Works
A fibre laser, as the name suggests, is created using a fibre optic cable, similar to one used for data transfer. Banks of laser diodes emit light, which is channeled through the fibre. The light is then amplified and channelled, being focused into a lens and emitted as a laser beam. This is far simpler than other forms of lasers, negating the need for optical mirrors, instead creating light intensity through the fibre optic cable. The fibre laser is also air cooled, requiring no additional coolants. This adds to the compact setup, and allows it to be integrated into existing production lines and processes without issue.
Similar to a YAG laser, a fibre laser produces light with a wavelength within the near-infrared range, at around 1064 nanometres. This also makes it an ideal method of marking on metal surfaces.
Applications of Fibre Lasers
Due to being far more efficient and less expensive to run than YAG lasers, a fibre laser is an industry standard piece of equipment in many manufacturing facilities. In fact, the creation of the laser beam is 200% more efficient than a CO2 laser. This, alongside having no expensive mirrors or removable focusing lens, make fibre lasers the most practical choice in applying permanent marks to metal components for modern manufacturers.