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 Lasers
and the EyePDF-file
General
Laser Safety Guidelines
Optical
Tweezers Safety Precautions
Laser
Safety Classification
Laser
Safety Links
Example for a
Laser Safety Calculation
Lasers and
the Eye
The
unprotected human eye is extremely sensitive to laser radiation
and can be permanently damaged from direct or reflected beams. The
site of
ocular damage for any given laser depends upon ist output wavelength.
Lasers in the visible (VIS) and near infrared (NIR) range of the
spectrum can cause retinal injury, since the cornea and the lens
of the eye are transparent to these wavelengths. Furthermore the
lens of the eye focusses the laser beam down to a very small spot
of the retina, increasing the energy density in the resulting spot
tremendously. Even a low power laser (with a few milliwatts) can
cause a burn on the retina - especially in darkend space, where
no other light sources are present, and the eye is focussed to infinity.
Wavelenghts outside this region (UV, IR) are absorbed by the anterior
segment of the eye, causing damage to the cornea and/or to the lens.
The extent of ocular damage is determined by laser irradiance, exposure
duration and beam size. The eye has a self defense mechanism, the
blink or aversion response. This may defend the eye from damage
where very low power and visible lasers are involved, but can not
protect the eye where higher power or NIR lasers are concerned.
By the time the eye reacts, the damage is already done.
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General
Laser Safety Guidelines
-> Never look into the beam of any
laser. How bright a beam appears has no bearing on the power level.
It could emit any wavelength at any power. IR laser are invisible
and even more dangerous, because your blink and aversion reflexes
don't work, since you can't see the beam.
-> Specular reflections may be just
as dangerous as the raw beam.
-> Always wear a proper set of eye
goggles, especially when working with lasers rated for Class IIIb
and Class IV. Take care you have the specific protection depending
on your laser wavelength and power. The worst thing is to think
you are protected when you are not.
-> Always block all beams you don't
use. Terminate the laser beam with a light absorbing material or
diffuse screen.
-> Instruct anyone else, who is working
insight the room to the hazards of laser light, and make sure, they
understand all.
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Optical
Tweezers Safety Precautions
Lasers used in optical tweezers have potential to damage the retina.
In case of invisible infrared lasers special care must be taken,
because injury due to exposure may be initially undetected until
thermal damage has occured. The retina lacks of pain sensory nerves
and, since the radiation is invisible, the aversion response of
the eye does of course not work. Special care must be taken at the
eyepieces of the microscope. The simplest method is to remove the
eyepieces and close the holes of the microscope head. If the eyepieces
are used, proper filters must be installed and carefully tested.
Be sure that they are installed permanently (into the head!) and
can not be accitendally removed. Be careful when adjusting your
optics. Always do your alignments using the minimum laser power
possible. Check for strays every time you realign, also at full
operating power. Laser beams should always propagate in a plain
parallel to the optical board. If the laser is on, do not bring
your eyes to this plain. Fasten your mirrors, lenses and other optical
devices tide, so they can not move by chance, generating dangerous
beams. Always wear laser safety googles until you turn off the laser.
Be aware, that your neck and head are not protected.
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Laser Safety
Classifications
All lasers are classified by the manufactorer and labelled with
the appropriate warning labels.
-> Class I Lasers:
Lasers that are not hazardous for continuous viewing, or are designed
in such a way that prevent human access to laser radiation [P<0,39µW].
-> Class II Lasers:
Lasers emitting visible light which, because of human aversion response,
do not normally present a hazard. Viewing directly over an extented
period of time would cause injuries [P<1mW].
-> Class IIIa Lasers:
Lasers that normally would not cause injury to the eyeif viewed
momentarily but would present a hazard if viewed using collection
optics [P<5mW].
-> Class IIIb Lasers:
Lasers that present an eye or skin hazard for both, direct beam
and specular relections. Viewing diffuse reflection does not produce
hazards, except at close proximity [P<500mW].
-> Class IV Lasers:
Lasers that present an eye hazard from direct, specular and diffuse
reflections. Furthermore, those lasers may produce fire hazards
and skin burns.
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Laser Safety
Links
Laser
Institute of America
Sam's
Laser FAQ - Laser Safety:
a comprehensive page, concerning a variety of
topics around laser safety
University
of Waterloo - Laser Safety Manual
Institute
of Laser Medicine (German)
Heinrich Heine Universität Düsseldorf, Germany;
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last modified: January 5, 2001
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