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HEALTH & SAFETY
1-12 L025317 Issue 5 July 2014
Beam Stop Guard
A beam stop guard is required for applications where guarding material is
fitted within 100mm of the laser lens focal plane. The beam stop is to
prevent burn through of the guard should the laser be repeatedly operated
without the substrate in position. The beam stop must be capable of
absorbing the full output power of the laser for a period of eight hours and
be large enough to cover the complete laser marking field area.
Materials
All guard materials must be opaque to 9 to 11 micron wavelength laser light
produced by the CO
2
laser. Guards may be metallic, however if a see-
through guard is required Makrolon® 099 from Bayer AG may be used.
A metallic guard with low reflectivity must be used. The housing must be
orientated in a way that no laser light is reflected back to the laser as the
reflected light may damage the laser.
The thickness of the guard material depends on the mechanical strength
required for stable housings, and the amount of ‘burn through’ anticipated.
For the purpose of
adequate mechanical rigidity and laser safety, a
thickness of at least six millimetres for 10W 30W laser systems and a
thickness of at least eight millimetres for 60W laser systems is
recommended. To ensure laser safety a greater thickness of the guard
material may be required.
Housings made from Makrolon® 099 must be installed within a minimum
distance of the laser lens of:
• 4 times the focus distance for 10W and 30W systems.
• 5 times the focus distance for 60W systems.
These distances are important to eliminate mirror reflection from any
surrounding parts.
In a fault condition, these materials withstand the laser beam for a limited
time before the beam burns through. The laser must therefore be monitored
to avoid a risk of fire.
A ceramic or metal plate may be used as a beam stop. A greater thickness
is required to achieve an “eight hour burn through” requirement.
Guidance regarding laser guards can be found in EN60825-Part 4.
Substrate
Laser Beam Path
Access Guard
Laser Head
Lens
Beam Stop