Download Working with lasers. - Optical Sciences Group

Working with lasers.
Laser Safety, ANP 6 nov. 2014.
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Can I use these goggles?
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The sun is the brightest source.
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Eye “reference” values:
• Sunlight: 1000 W/m2 (= 1 mW/mm2)
• Pupil range Ø: 3 – 7 mm (7 –38 mm2)
• Optical power received by the eye:
7 – 38 mW
• Eye blink reflex: 0.25 sec.
(only applicable in the visible area)
Laser Safety, ANP 6 nov. 2014.
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The human eye (simplified).
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Types of photoreceptors
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Distribution of rods and cones
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Wavelength (λ) and impact.
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Classification EN 60825-1
• Class 1:
1M:
• Class 2:
2M:
• Class 3R:
3B:
• Class 4:
always safe
always safe without focusing
safe, due to the blink reflex, <1mW
safe, without focusing
low risk of injury, restricted beam
viewing, <5mW
direct exposure = eye hazard, <0.5W
ALL OTHER LASERS
Laser Safety, ANP 6 nov. 2014.
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(il)legal? purchases…
Dutch legislation
Source: Informatieblad 26 / 4 september 2006, Voedsel en Waren Autoriteit:
• Laserpointer: no selling of class 3R, 3B and 4.
• Lasergadget: no selling of class 2, 2M, 3R, 3B and 4.
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Not always a laser…..
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Maximum Permissible Exposure
• Typically set at 10% of the dose creating damage with a
probability of 50%, worst case conditions.
• Basis for selecting laser goggles.
Warning symbol
class 2 and up.
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MPE in W/cm2 .
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MPE in J/cm2.
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MPE in J/cm2.
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Eye protection terminology.
Example of EN 207 specifications
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EN 207 laser working modes.
EN 207 specifies four laser working modes:
Working mode
Letter
Pulse length
Continuous mode
Pulsed mode
Giant pulsed mode
Modelocked
D
I
R
M
> 0.25 s
>1 μs–0.25 s
1 ns–1 μs
< 1 ns
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EN 207 scale numbers.
Range: L1-L10, Ln means that OD > n; n=0: no protection.
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Example 1, Q
• A laser operates at 1064 nm and has a
pulse duration of 10 ns, 103 J/m².
You have goggles that are specified as
DIR 1064 L5
• Do these goggles offer suitable protection
for this particular laser?
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1064nm/10ns/
103 J/m²
Example 1, A
DIR 1064 L5 ??
The pulse duration
indicates that we should
look at the
R specification,
with scale number n=5,
which gives an upper
limit of 5×102 J/m²,
which means that these
goggles do not offer
suitable protection for
this particular laser.
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Example 2, Q
• A laser operates at 780 nm, is continuous
wave with a power density of
P = 500 W/m².
• Does a D 780 L2 rated goggle offer
suitable protection for this particular laser?
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780nm CW,
P=500W/m2
Example 2, A
D 780 L2 ??
• You need a D
protection level of
log(500) − 1 =
1.69, which is
rounded up to 2.
In other words,
the safety
goggles should
be at least
• D 780 L2.
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Case: Fianium SC400-4
What goggles to buy ????
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Case: Fianium SC400-4
•
•
•
•
Pulse width: 6 ps
Total power: > 4 W
Rep. Rate: 40 MHz
Beam diameter at 633 nm: 1.5 mm
Peak power = 17 kW
Peak Energy = 100 nJ
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Case: Fianium SC400-4
• MPE curve not directly applicable (λ dependancy)
• Calculate energy density for open pupil area: 100e-9 / 0.39 =
25e-8 J/cm2 = 25e-4 J/m2 .
In 0.25 s, 10e6 (=N) pulses occur, thermal correction factor N1/4
applies (EN 60825). Cp=(10e6)0.25 = 56.
Attenuation needed = log(E/1.5)+4= 3.0.
• DC calculation: log(P)-1 = log(4/0.39*1e4)-1 = 5.0-1 = 4.0 (!)
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Case: Fianium SC400-4
Transmitted: ~7 mW , still not safe.
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Case: Fianium SC400-4
2. LaserVision T1L01, VLT = 30 %, € 860.-
From 1400 nm to
2400 nm: ~OD4.
Transmitted: 60 mW , OD needed = 2.2
Conclusion: still not safe.
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Case: Fianium SC400-4
3. Thorlabs LG2, VLT = 19 %, € 156.-
Transmitted (vis): 105 mW , OD needed 2.4
Conclusion: still not safe.
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Case: Fianium SC400-4
100 % protection
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Goggles, summary.
•
•
•
•
Consult the laser manufacturer
Consider the Visible Light Transmittance
Consider comfort
Keep the goggles in good shape
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Enclosure, black cloth curtain
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Good practice in beampath design.
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Top 14 of laser related injuries,
Rockwell Laser Industries
• Unanticipated eye exposure during alignment.
• Misaligned optics and upwardly directed beams.
• Available laser eye protection was not used.
•
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Equipment malfunction.
Improper method of handling high voltage.
Intentional exposure of unprotected persons.
Operators unfamiliar with laser equipment.
No protection provided for associated hazards.
Improper restoration of equipment following servicing.
Incorrect eyewear selection and/or eyewear failure.
Accidental eye/skin exposure during normal use.
Inhalation of laser-generated fume or viewing of secondary radiation (UV, blue light).
Laser ignition of fires.
Photochemical eye or skin exposure.
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Laser accidents are:
• - High impact
• - Low probability
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To err is human
• Key to safety: Protocol, multiple lines of
defense.
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Thank you!
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Luminosity function of the eye.
Wavelength [nm]
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Good practice in beampath design.
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Enclosure, black plastic curtain
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