R. James Rockwell, Jr.

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A LASER PROTECTIVE BARRIER TESTING METHOD

• R. James Rockwell, Jr.
• ROCKWELL LASER INDUSTRIES

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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?

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

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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).

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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.

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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

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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.

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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?

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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

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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
• NdYAG at 1064 nm
• Argon at 514 nm
• The other factors must await yet further
  testing...

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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.

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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

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TYPICAL LASER BARRIER TESTING
Laser barrier test showing various test spots
at different
radiant exposure levels
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Laser Protective BarrierPenetration Threshold
levels for four different barriers
NdYAG Laser _at_ 1064 nm Argon Laser _at_ 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)
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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.

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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.