Transcript COURSEPAGE-DUMP_BMD407-LASERS-AND-FIBEROPTICS

Laser Safety
Judy Donnelly
Three Rivers Community College
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CHARACTERISTICS of LASER LIGHT
 Monochromatic- “single color”
 Coherent- waves are “in phase”
 Highly Directional- resulting in very concentrated light
energy (high “irradiance”)
Judy Donnelly
Three Rivers Community College
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COMPARE LIGHT FROM A LASER AND A FLASHLIGHT
 Monochromatic
 laser is single color; flashlight has rainbow spectrum
 Coherent
 Laser Speckle- due to wave interference
 Highly Directional
 Flashlight beam spreads much more than laser’s
 Define Irradiance = Power/area; laser is lower power
but much smaller area
Judy Donnelly
Three Rivers Community College
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What is Irradiance?
Irradiance depends on both laser power and on the area being
irradiated. It is a concept of central importance in laser safety. The
symbol for irradiance is “E”, and the units are usually mW/cm2.
E=
P
A
Judy Donnelly
Three Rivers Community College
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EXAMPLE: CALCULATION of IRRADIANCE
A 5 mWatt laser makes a 2 mm by 3 mm spot on a wall.
Find the irradiance.
Power = 5 mWatt
Area = 0.2 cm x 0.3 cm = 0.06 cm2
Irradiance = Power/Area = 5 mWatt / 0.06 cm2
= 83 mWatt / cm2
Judy Donnelly
Three Rivers Community College
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Laser Safety Standards
Several organizations oversee standards for laser safety:
ANSI American National Standards Institute
Reference for laser users
CDRH Center for Devices and Radiological Health
Product safety standards for laser manufacturers
OSHA Occupational Safety and Health Administration
Enforces regulations in the workplace
IEC International Electrotechnical Commission
International standards organization, with 60 member countries
Judy Donnelly
Three Rivers Community College
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Laser Eye Hazards
The eye is the part of the body most vulnerable to laser hazards. Changes
to the eye can occur at much lower laser power levels than changes to the
skin. And, eye injuries are generally far more serious (life altering) than
injuries to the skin.
lens
cornea
retina
fovea
optic nerve
pupil
iris
Judy Donnelly
Three Rivers Community College
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Absorption of Light by the Eye
Lens
Cornea
Retina
Mid and Far
IR(1400 nm-1
mm)
Mid UV
(180 nm-315 nm)
Laser Wavelength Region
IR-C = 1 mm to 1400 nm
IR-B = 3000 nm to 1400 nm
Near UV
(315 nm-400 nm)
IR-A = 1400 nm to 700 nm
Visible light = 700 nm to 400 nm
UV-A = 400 nm to 315 nm
UV-B = 315 nm to 280 nm
Visible and Near IR
(400 nm-1400 nm)
UV-C = 280 nm to 100 nm
Judy Donnelly
Three Rivers Community College
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Irradiance at the Retina
Example
A laser pointer produces a 2-mW beam. The beam enters the eye and is
focused by the cornea and lens to a spot on the retina 16 um in diameter.
Find:
The irradiance on the retina, assuming that all of the 2 mW of power is
focused on the retina.
Solution:
Area of spot
A = d2/4
= (1.6 x 10-3cm)2/4
= 2 x 10-6 cm2
lens
cornea
retina
Irradiance:
pupil
E = P/A
= 2 mW/[2 x 10-6 cm2]
= 1000 W/cm2
Judy Donnelly
Three Rivers Community College
Rule of thumb: The optics of
the eye increase irradiance
by a factor of 100,000!
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Example of retinal damage due to laser exposure
Judy Donnelly
Three Rivers Community College
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Not all viewing conditions are the same
Specular reflection
Convex reflector
Concave reflector
Whether a reflection is specular
or diffuse for a given surface
depends on the laser
wavelength. “Smooth” is relative
to the laser wavelength.
Diffuse reflection
Judy Donnelly
Three Rivers Community College
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LASER SKIN HAZARDS
•Thermal hazards (skin burns) from high level of optical
radiation
•Photochemical hazards (accelerated aging and risk of
skin cancer) due to ultraviolet radiation
Judy Donnelly
Three Rivers Community College
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NONBEAM HAZARDS
There are several nonbeam potential hazards associated with the
use of lasers and laser systems.
1.
2.
3.
4.
5.
6.
Fire hazard
Explosion hazard
Electrical hazard
Chemical hazard
Laser generated air contaminants (LGAC)
Other hazards
Although loss of sight may be life altering, electrocution is the hazard
most likely to end life!
Judy Donnelly
Three Rivers Community College
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NONBEAM HAZARDS
 FIRE
HAZARD
Class 4 laser systems represent a fire hazard.
Irradiances exceeding 10 W/cm2 or beam powers exceeding 0.5 W.
The use of flame-retardant materials is advisable and necessary.
Fires have occurred in medical facilities where oxygen provides an
explosive environment.
Judy Donnelly
Three Rivers Community College
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NONBEAM HAZARDS
 EXPLOSION HAZARD
High-pressure arc lamps, filament lamps, and capacitor banks in
laser equipment shall be enclosed resulting from component
disintegration.
The laser target and elements of the optical train that may shatter
during laser operation shall also be enclosed or equivalently
protected to prevent injury to operators and observers.
Explosive reactions of chemical laser reactants or other laser gases
may be a concern in some cases.
Judy Donnelly
Three Rivers Community College
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 NONBEAM
HAZARDS
ELECTRICAL HAZARD
This may occur from contact with exposed utility power use, device
control, and power-supply conductors operating at potentials of 50
volts and above.
These exposures can occur during laser setup or installation,
maintenance, and service
Judy Donnelly
Three Rivers Community College
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NONBEAM HAZARDS
ELECTRICAL HAZARD
The following potential problems have frequently been identified during laser
facility audits.
1.
Uncovered electrical terminals
2.
Improperly insulated electrical terminals
3.
Hidden “power-up” warning lights
4.
Non-earth-grounded or improperly grounded laser equipment
Judy Donnelly
Three Rivers Community College
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NONBEAM HAZARDS
CHEMICAL HAZARDS
Certain dyes are highly toxic or carcinogenic.
These dyes frequently have to be changed, special care must be
taken when handling, preparing solutions, and operating dye lasers.
Judy Donnelly
Three Rivers Community College
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NONBEAM HAZARDS
LASER GENERATED AIR CONTAMINANTS
LGAC result from the interaction of high-energy laser radiation,
assist gases used in material processing, and the material itself.
When lasers are used in a medical setting, particles of biological
origin such as bacteria may be released into the air. Air filters and/or
ventilation systems are usually required.
Judy Donnelly
Three Rivers Community College
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NONBEAM HAZARDS
OTHER HAZARDS
•Compressed gases
•Cryogenic liquids
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Three Rivers Community College
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Laser Hazard Classifications
Class 1: Cannot, under normal operating conditions, emit a
hazardous level of optical radiation.
Included in this category is laboratory equipment using lasers
with all beam paths and reflections enclosed. These are called
“embedded lasers.”
Examples:
• very low powered lasers (< 0.4 microwatts)
• CD players, laser printers
Class 1M (NEW!) Eye safe unless focused by a optics
Judy Donnelly
Three Rivers Community College
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Laser Hazard Classifications
Class 2: low-power visible laser of more than 0.4 microwatts but
less than1 milliwatt. The eye is protected by the “blink reflex.”
That is, the laser does not have enough output power to injure a
person accidentally, but may injure the eye when stared at for a
long period.
A “caution” label is required.
Examples:
• Many low power HeNe lasers, especially in school labs
• Lasers used for alignment procedures
• Bar Code scanners
Class 2M (NEW!) Visible output, less than 1 mW, eye safe unless
focused by a optics
Judy Donnelly
Three Rivers Community College
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Laser Hazard Classifications
Class 3a lasers—rated in power from 1 milliwatt to 5 milliwatts
Will not normally injure a person when viewed briefly with the unaided
eye but may cause injury when viewed with a focusing device such as a
lens or telescope.
A danger or caution sign must label the device, depending on its
irradiance.
Examples:
• many red laser pointers
• some HeNe lab lasers
IEC Class 3R is similar.
Judy Donnelly
Three Rivers Community College
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Laser Hazard Classifications (continued)
Class 3b lasers from 5 milliwatts to 500 milliwatts can produce eye
injury when viewed without eye protection.
This class of laser requires a danger label and could have dangerous
specular reflections.
Eye protection is required.
EXAMPLES :
•12 mW HeNe
•50 mW HeCd
Judy Donnelly
Three Rivers Community College
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Laser Hazard Classifications (continued)
Class 4 lasers above 500 milliwatts in power can injure you if viewed
directly or by viewing either the specular and diffuse reflections
of the beam.
These lasers can also present a fire hazard.
A danger sign will label this laser.
Eye and skin protection are required.
Judy Donnelly
Three Rivers Community College
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MAXIMUM PERMISSIBLE EXPOSURE (MPE)
Maximum permissible exposure (MPE) limits indicate the greatest
exposure that most individuals can tolerate without sustaining injury.
MPE depends on:
• Wavelength
• Output Energy and Power
• Size of the Irradiated Area
• Duration of Exposure
• Pulse Repetition Rate
MPE is usually expressed in terms of the allowable exposure time (in
seconds) for a given irradiance (in watts/cm2) at a particular wavelength.
MPE’s are useful for determining optical densities for eyewear, filters or
windows.
Judy Donnelly
Three Rivers Community College
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Nominal Hazard Zone (NHZ)
This zone describes the region within which the level of direct, reflected, or
scattered (diffuse) laser radiation is above the allowable MPE. The distance
depends on whether or not the beam is direct, focused, or diffused, as well
as the power and
MPE.
LASER
d
f0
NHZ
NHZ illustrated for a focused laser beam
Judy Donnelly
Three Rivers Community College
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Choosing laser eyewear: Optical Density
 The ability of a material to absorb light is sometimes
expressed in terms of optical density.
 Optical density is a logarithmic quantity.
 In terms of optical density (OD), transmittance is:
T  10
OD
Judy Donnelly
Three Rivers Community College
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Optical Density
Example:
Laser goggles with OD = 2 at a particular wavelength
have a transmittance of
T  10
2
 0.01
The goggles transmit 1% of the incident light at the
specific rated wavelength.
Judy Donnelly
Three Rivers Community College
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Optical Density
T = 10-OD
OD
Transmission
%Transmission
0
1
1.0
100%
1
10–1
0.1
10%
2
10–2
0.01
1%
3
10–3
0.001
0.1%
4
10–4
0.0001
0.01%
5
10–5
0.00001
0.001%
6
10–6
0.000001
0.0001%
7
10–7
0.0000001
0.00001%
Judy Donnelly
Three Rivers Community College
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Choosing the Optical Density for laser glasses
To determine the required OD for safety glasses, compare
the irradiation incident on the eye(Eo) to the MPE
(what is allowed to be transmitted to the eye) and take
the log of the ratio.
 Eo 
OD  Log10(T)  Log10
MPE 



Judy Donnelly
Three Rivers Community College
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SAFETY RULES FOR LAB LASERS
1.
Avoid looking directly into any laser beam or at its reflection.
Be aware of the beam’s location.
1.
Only trained qualified personnel should work with lasers
Don’t let friends and visitors to the lab play with the lasers
1.
Keep room lights on whenever possible
2.
Remove all watches, jewel and unnecessary specular (shiny) reflecting
surfaces from the work area.
3.
Don’t bend down below beam height
4.
Use beam blocks
5.
Wear laser safety eyewear
6.
Report accidents immediately.
In the case of eye exposure consult an opthalmologist.
Judy Donnelly
Three Rivers Community College
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