Appendix A
Laser Safety Guidelines
54
Copyright © 2010, Harris Corporation
General Laser
Information
Conventional lasers can produce an intense beam of monochromatic light. (The
term “monochromaticity” means a single wavelength output of pure color that
may be visible or invisible to the eye.) A conventional laser produces a small-sized
beam of light, and because the beam size is small the power density (also called
“irradiance”) is very high. Consequently, for their safe operation, lasers and laser
products are subject to federal and applicable state (USA) regulations, as well as
international standards.
A conventional laser beam expands very little over distance, or is said to be very
well “collimated”; thus, conventional laser irradiance remains relatively constant
over distance. Lasers used in lightwave systems, however, have a large beam
divergence, which is typically 10 to 20 degrees. Here, irradiance obeys the inverse
square law (doubling the distance reduces the irradiance by a factor of 4) and
rapidly decreases over distance.
Lasers and
Eye Damage
The optical energy emitted by laser and high-radiance LEDs in the 400-1400 nm
range may cause eye damage. When a beam of light enters the eye, the eye
magnifies and focuses the energy on the retina, magnifying the irradiance. The
irradiance of the energy that reaches the retina is approximately 10
5
or 100,000
times more than at the cornea and, if sufficiently intense, may burn the retina.
The damage mechanism at the wavelengths used in an optical fiber
telecommunications is thermal in origin, i.e., damage caused by heating. A specific
amount of energy is required for a definite time to heat an area of retinal tissue.
Damage to the retina occurs only when you look at the light sufficiently long that
the product of the retinal irradiance and the viewing time exceeds the damage
threshold. Optical energies above 1400 nm cause corneal and skin burns but do
not affect the retina. The thresholds for injury at wavelengths greater than 1400
nm are significantly higher than for wavelengths in the retinal hazard region
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