“What laser wavelength is best?” This inevitable question occurs when considering laser markers for processing applications. Every wavelength has strengths and weaknesses; understanding their fundamental characteristics is key to becoming a laser processing expert.
Infrared (or IR) lasers are the most common and versatile systems used for laser processing. As the name implies, IR lasers use light outside of the visible spectrum (i.e. longer than 780 nm). These systems can range anywhere from low-power processing machines to high-power laser engraving machines.
Lasers with 1064 nm wavelength include:
• YAG lasers
• YVO4 lasers
• Fiber lasers
• A wide range of applications from resins to metals
• Cannot process transparent objects like glass as the laser passes through such objects
• Creates contrast on resins easily
CO2 lasers markers have 10 times the wavelength of YAG, YVO4 and Fiber systems. This is the longest wavelength commonly found among industrial lasers. CO2 lasers generate the laser medium through stimulation of CO2 gas.
CO2 laser engravers are the only markers with a 10600 nm wavelength.
• Not absorbed well by metals
• Melting and burning occur due to the long wavelength and heat transfer
• Processing transparent objects such as glass and PET is possible
• Contrast printing and discoloration are generally not possible
Second Harmonic Generation (SHG) lasers use half the typical 1064 nm wavelength. 532 nm falls into the visible spectrum and is green in color. This wavelength is produced by transmitting a 1064 nm wavelength through a nonlinear crystal that reduces the wavelength. A YVO4 medium is normally used because the characteristics of the beam are well suited for intricate processing.
Lasers with a 532 nm wavelength range include:
• YVO4 SHG lasers
• YAG SHG lasers
• High absorption rates in materials that do not react well with typical IR wavelengths and those that reflect IR light (such as gold and copper)
• Intricate processing is possible because of a smaller beam spot than IR lasers
• Processing transparent objects is typically not possible
• High peak power without large amounts of heat transfer makes SHG lasers ideal for micro machining and intricate designs
Third Harmonic Generation (THG) lasers use one-third of the typical 1064 nm wavelength. These systems fall into the ultraviolet (UV) range of light, and are commonly referred to as UV laser markers.
A YVO4 or YAG laser is used to produce the fundamental wavelength and then is transferred through a nonlinear crystal to reduce the wavelength to 532nm and then a second nonlinear crystal to reduce the wavelength to 355 nm.
Lasers with a 355 nm wavelength include:
• YVO4 THG lasers
• YAG THG lasers
• UV light has extremely high absorption rates in most materials and does not apply excessive amounts of heat.
• A very small beam spot makes very fine processing possible.
• Able to achieve high contrast on a wide variety of materials
IR light causes a thermal reaction in most materials, whereas shorter wavelengths tend to cause photochemical reactions. Shorter wavelengths can produce a small beam radius, allowing for more intricate processing and applying less heat to the material.
For processing large or very thick targets a specialized machine is generally needed. These points should be taken into consideration when purchasing a laser for processing.