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19.8.2019

Laser safety

Question that many of our customers wonder is that how hazardous laser light is. Laser light is very energetic and can still be hazardous even if observed from tens of meters away. This is valid concern if we observe raw laser beam emitted straight from the laser isolator that has low divergence. In laser marking, the beam goes first through scanner mirrors before focusing through lens. Scanner makes focused laser beam move very fast on marked surface and reflect energetic laser light to large angular space. Lens causes same kind of effects to laser light. When light focuses to very small spot on the working area it converges up until it reaches the laser focus. If focus reflects from surface, the beam diverges while it moves away from the focus.

Divergence makes laser beam diameter grow faster and at the same time lose its hazardous intensity in shorter distance. This means that lenses with shorter focal length also have shorter hazardous distance when reflected from marked surface. However, lenses with short focal lengths also have smaller working area. Laser light intensity decreases even more due to diffuse reflection from the marked surface. Diffuse reflection means reflection following Lambert’s cosine law. This makes reflected laser light on the marked surface act like Lambertian emitter. Lambertian surface looks as bright observed from all angles. In laser marking, the marked materials reflect diffusely in almost every case.

Even though all these aspects reduce laser hazards significantly it is always better to be prepared for the worst-case scenario. There might be some error situation where scanner mirrors get stuck and laser beam stays on same spot of the working area laser still emitting full power. Normally in this situation focused spot modifies the surface geometry making it more diffusive and less hazardous in the distance. Powerful laser light also heats up the surface increasing the absorptivity to the material and decreasing the reflectivity correspondingly. Even in this situation there might be some durable and reflective mirror on the working area that does not diffuse or absorb the laser energy and laser experiences mirror-like specular reflection from the surface. For these reasons it is good practice to handle the case as if the laser reflects from mirror-like surface.

Safe nominal ocular hazard distances (NOHD) for laser devices can be calculated but it is always better to build protective housing between operators and laser radiation. This way uncertainty among users concerning adequate laser protection can be reduced significantly.

Cajo lasers and safety

Cajo offers a wide range of Class 1 complete marking solutions with convenient protective enclosure and radiation cover. With integrable laser units (Cajo Tailor series) we will help the customer to design or to find an applicable partner to design the protective cover or enclosure to meet the specific needs for the application.

There are several ways to ensure safe working area around the laser unit. You can build a protective enclosure meeting the industry standards. Laser light can be blocked with an acrylic protective filter on the observation window, so that you are able to control the marking process with direct view to the product. You can also include protective goggles into your order from Cajo: ask more from your sales representative! Protective goggles are intended to protect eyes from scattered light and should not be used against exposure to direct or reflected light.

Writer Antti Kauppila is working as Laser and Optics Specialist at Cajo Technologies

KEY WORDS: Laser Marking, Laser, Safety, Standards, Radiation

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