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Ageing resistance of laser protection filters

Project number: F 2442 Institution: Federal Institute for Occupational Safety and Health (BAuA) / Bayerisches Laserzentrum GmbH Status: Completed Project

Description:

The intended protection of laser protection filters and laser protection goggles is an important component in the application of personal protective measures for the safe operation of high power lasers. In the course of time, the protective effect can be reduced or even reduced to ineffectiveness by use or by material-related processes within the filter materials.

The reduction of the protective function of an aged or used protective goggles with scratches, opacities, fading, etc., has not been quantified so far. Even for laser protection specialists, no criteria are available for easily assessing the protection of an aged protective goggle.

Neither the laser protection filters that were artificially aged in laboratory by means of UV radiation nor those filters actually aged in practice by using them showed a critical decrease in their protection efficiency. In the case of artificially aged PMMA filters, however, the optical parameters scattered light and light transmission reached the limits defined in standard EN 168.

It can be concluded that laser resistance is no limiting criterion with regard to the aging of PMMA and PC laser protection filters for the examined laser wavelengths 1,064 nm and 10,600 nm. Even after 200 hours of UV irradiation, which would correspond to several years of direct sunlight exposure, for example, due to false storage conditions, only a slight decrease in the laser resistance emerges, but the measured filter resistance times still are far above the applied standard. A similarly positive outcome was found for the “naturally” aged filters used in practice. Comparing the examined old filters with identical new ones regarding laser resistance, no critical change in the protection efficiency was present. Therefore, people wearing laser safety glasses should rather pay attention to the goggle’s apparent overall condition including possible damage than to its mere age.

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