Transcript Laser safety

Laser safety
Paul van Kampen
02/02/11
Almost all you need to know
about laser safety
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Beware of electrical safety
Don’t expose your eyes or skin
Minimise the number of shiny surfaces
Wear goggles
Beware of water leaks
Use warning signs
Use interlocks
Types of laser
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Continuous wave (cw) or pulsed
Power
Wavelength
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Visible/invisible
Effect on skin, cornea, retina
Laser classification
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What is it based on?
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Maximum Permissible Exposure (MPE)
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10% of dose that has 50% chance of doing damage
Depends on wavelength, body part, cw or pulsed
Visible-IR range, cornea, cw: 1 mW/cm2
Example: class 1 or class I laser limit
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Fully dilated pupil: diameter 7 mm, area 0.39 cm2
Maximum permissible power: 0.39 mW
Laser classification (old)
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Class I: safe (UNFOCUSSED!)
Class II: safe - your aversion to bright light
will protect you
Class IIIA: cw: 1-5 mW, safe unless you look
at it, or its reflection, directly
Class IIIB: cw 5-500 mW, pulsed <10 J/cm2,
sometimes diffuse reflection hazard
Class IV: cw >500 mW, pulsed >10 J/cm2,
diffuse reflection, fire, skin hazard
More data become available
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More data become available
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Laser classification (new)
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Class 1(M): safe (UNFOCUSSED!) <0.4 mW
Class 2(M): safe - your aversion to bright light
will protect you. <1 mW
Class 3R: cw: 1-5 mW, safe unless you look
at it, or its reflection, directly. Low risk
Class 3B: cw 5-500 mW, (<300 mW visible),
pulsed <10 J/cm2, diffuse reflection OK
Class 4: cw >500 mW, pulsed >10 J/cm2,
diffuse reflection, fire, skin hazard, interlock
required
UV lasers
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Excimer lasers: gas premix typically contains 0.1
percent of fluorine/chlorine
ArF, KrCl, KrF: UV-C radiation
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XeCl: UV-B radiation
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Eye: snowblindness
Skin: sunburn, skin cancer
Eye: snowblindness
Skin: skin aging, increased pigmentation
XeF, Nd:YAG tripled: UV-A radiation
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Eye: cataracts
Skin: skin burn, pigment darkening
Germicidal lamps
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15 W UV-C lamp 254 nm, cylindrical, 30 cm tall
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40% efficient in UV-C so 6 W of UV-C light
Model: every ring 1 cm high centred on lamp
transmits a total of 200 mW outward
Irradiance of 30/r mW/cm2 at r cm from lamp
Skin/eye MPE = 3 mJ/cm2, cumulative so
MPE = 3/t mW/cm2 for exposure of t seconds
For every second of exposure, you must be about
10 cm from the lamp
Place lamp in enclosed reflective chamber
WEAR GOGGLES & DON’T EXPOSE SKIN
Germicidal lamps (2)
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What about cooling
tube made of Pyrex?
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Transmits ~80% in UVC range
(Some sources give
cut-off as 300 nm)
Almost no protection
Perhaps not
surprising – the lamp
kills bacteria in 5
seconds!
Visible/IR lasers
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CW/pulsed:
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protect your eyes
blue-green worse than red-infrared
don’t shoot at your skin
Dye lasers: dyes are carcinogens
CO2 lasers: fire hazard
Good lab design
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Often a competition between hazards:
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Water
Electrical
Trip
Laser radiation
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Scatter
Direct exposure
Good management is mostly common sense
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e.g., don’t forget to remove your watch!
A laser lab (1)
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Data:
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Vacuum chamber
Pulsed IR class IV laser
Target 10 cm behind glass
Target 1.5 m above floor
Lens: F.L. 20 cm
Lens holder: aluminium
Can you do better?
A laser lab (2)
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Beam height:
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Unsafe for people >5 ft
If you can’t adjust target,
move beam out of the way
Door:
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Don’t shoot laser in that
direction!
Make sure the system is
interlocked – door open,
laser off
A laser lab (3)
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Lens:
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Beware of scatter
Each surface reflects 4% as
a mirror (back into laser!)
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You may hit lens holder
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AR coating
Turn lens around
Spray paint black
Window:
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4% reflection focused on
lens
A laser lab (4)
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Adaptability
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Tripping:
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Can’t easily adjust beam
Water/electrical leads all
over the floor
Invisibility
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Can you mount a collinear
visible alignment laser?
A laser lab (5)
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Possible solution:
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Collinear weak visible laser
Shorter FL lens
Turn lens or beam dump
Piped beam
Mirrors allow manipulation
Laser against wall
Beware of pushing against
piping
Curtain/screen near door
curtain/
screen