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A LASER PROTECTIVE BARRIER TESTING METHOD

A LASER PROTECTIVE BARRIER TESTING METHOD. R. James Rockwell, Jr. ROCKWELL LASER INDUSTRIES. LASER BARRIERS AS A CONTROL. As the scope of laser controls more frequently include an area barrier as a means of either temporary or permanent protection, it

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A LASER PROTECTIVE BARRIER TESTING METHOD

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  1. A LASER PROTECTIVE BARRIER TESTING METHOD R. James Rockwell, Jr. ROCKWELL LASER INDUSTRIES

  2. LASER BARRIERS AS A CONTROL As the scope of laser controls more frequently include an area barrier as a means of either temporary or permanent protection, it becomes important to determine if the barrier can provide the protection that is needed. Simply stated...will the barrier withstand the laser beam long enough - without penetration - so that the operator can turn off the laser or take other actions to avoid the beam?

  3. TYPICAL LASER BARRIER USE Laser barrier used in a laboratory facility as a room divider to establish a temporary laser controlled area

  4. ANSI Z136.1 RECOMMENDS: 4.6.4 Laser Protective Barriers and Curtains, (Class 3b or Class 4). • A blocking barrier, or screen, or curtain which can block or filter the laser beam at the entryway should be used inside the controlled area to prevent the laser light from exiting the area at levels above the applicable MPE level.

  5. ANSI Z136.1 RECOMMENDS: 4.6.4 Laser Protective Barriers and Curtains, (Class 3b or Class 4). • Such laser barriers shall be specifically selected to withstand direct and diffusely scattered beams. In this case, the barrier shall exhibit a damage threshold for beam penetration for a specified exposure time commensurate with the total hazard evaluation for the facility and specific application. (See appendix C).

  6. ANSI Z136.1 RECOMMENDS: 4.6.4 Laser Protective Barriers and Curtains, (Class 3b or Class 4). • Important in the selection of the barrier are the factors of flammability and decomposition products of the barrier material. It is essential that the barrier not support combustion or release toxic fumes following a laser exposure.

  7. A METHOD TO RATE LASER BARRIERS One testing protocol would be to establish that no measurable beam penetration occurs: • For a maximum incident irradiance level • For a pre-selected exposure time (10-100 seconds have been suggested) • For a range of beam sizes

  8. A METHOD TO RATE LASER BARRIERS The irradiance level where No Measurable beam Penetration (NMP) occurs would be determined: • From this data, the highest exposure where penetration does not occur would be established as the Penetration Threshold Level (PTL) • The PTL could then provide a rating of whether such a barrier would withstand a specific "real world" laser exposure.

  9. A METHOD TO RATE LASER BARRIERS The PTL may be laser parameter dependent: • Previous studies have shown that laser exposures of some barrier designs yeild a PTL that is dependent on the laser beam size. • This raises the question as to what beam diameter size is the most appropriate in effecting the PTL rating - or - whether a range of diameters may be chosen?

  10. A METHOD TO RATE LASER BARRIERS At this time there is no testing protocol that has been established to rate the laser barriers: • The proposed protocol suggests to establish the PTL's for 100 seconds for a range of irradiance values and beam spot sizes, and... • To determine whether different PTL's are obtained using CW, pulsed and repetitively pulsed, and... • The PTL's at different laser wavelengths

  11. A METHOD TO RATE LASER BARRIERS This report will cover only: • Exposures for two CW lasers for a range of irradiance values and beam spot sizes: • The two laser wavelengths are: Nd:YAG at 1064 nm Argon at 514 nm • The other factors must await yet further testing...

  12. A METHOD TO RATE LASER BARRIERS • Thus, the testing reported here was done so-as-to determine the highest laser beam irradiance for which no measureable penetration occurred for a total exposure of 100 seconds for beam spot size diameter ranging from 4 - 6 mm.

  13. A METHOD TO RATE LASER BARRIERS • It is argued that during an accidental over-exposure condition, the laser would be turned-off or the beam otherwise terminated within the 100 second time factor

  14. TYPICAL LASER BARRIER TESTING Laser barrier test showing various test spots at different radiant exposure levels

  15. Laser Protective BarrierPenetration Threshold levels for four different barriers Nd:YAG Laser @ 1064 nm & Argon Laser @ 514 nm for 100 s. PTL 300 W/cm2 200 W/cm2 100 W/cm2 Irradiance (Wcm2) PTL criteria set at a 5 mm beam diameter 2 W/cm2 Laser Beam Diameter (mm)

  16. A SUMMARY OFTHE BARRIER TESTING The results showed: • The multi-layered laser barriers designs that were tested are usually not penetrated until a critical irradiance level is reached for a given beam size... • Then penetration occurs almost immediately! • Otherwise, the barrier would withstand the exposure for at least 100 seconds - if not significantly longer.

  17. CONCLUSION... The laser barrier testing protocol used appears to provide the desired end point... • A rating method for laser barriers that indicates the maximum exposure level where no measurable beam penetration occurs, ...and • The PTL value seems to provide a very simple rating which directly relates to typical “real world" laser exposure conditions.

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