Laser Classification - OPTOKON EDFA User Manual

EDFA optical amplifier – user manual

2.3 Laser classification

A laser is a light source that can be dangerous to the people exposed to it. Even low power
lasers can be hazardous to eyesight. A person exposed to laser radiation (especially
invisible radiation) may be unaware that damage is occurring. Some lasers are so powerful
that even the diffuse reflection from a surface can be hazardous to the eye. Laser radiation
predominantly causes eye injury via thermal effects on the retina. A transient increase of
only 10 °C can destroy retinal photoreceptors
Lasers have been classified by wavelength and maximum output power into four classes
and a few subclasses since the early 1970s. The classifications categorize lasers according
to their ability to produce damage in exposed people, from class 1 (no hazard during
normal use) to class 4 (severe hazard for eyes and skin). There are two classification
systems, the "old system" used before 2002, and the "revised system" being phased in
since 2002. The latter reflects the greater knowledge of lasers that has been accumulated
since the original classification system was devised, and permits certain types of lasers to
be recognized as having a lower hazard than was implied by their placement in the original
classification system. The revised system is part of the revised IEC 60825 standard. From
2007, the revised system is also incorporated into the US-oriented ANSI Laser Safety
Standard (ANSI Z136.1). Since 2007, labeling according to the revised system is accepted
by the FDA on laser products imported into the US. The old and revised systems can be
distinguished by the 1M, 2M and 3R classes used only in the revised system and the 2A
and 3A classes used only in the old system. Class numbers were designated using Roman
numerals (I–IV) in the US under the old system and Arabic numerals (1–4) in the EU. The
revised system uses Arabic numerals (1–4) in all jurisdictions.
The classification of a laser is based on the concept of accessible emission limits (AEL) that
are defined for each laser class. This is usually a maximum power (in W) or energy (in J)
that can be emitted in a specified wavelength range and exposure time. For infrared
wavelengths above 4 μm, it is specified as a maximum power density (in W/m2). It is the
responsibility of the manufacturer to provide the correct classification of a laser, and to
equip the laser with appropriate warning labels and safety measures as prescribed by the
regulations. Safety measures used with the more powerful lasers include key-controlled
operation, warning lights to indicate laser light emission, a beam stop or attenuator, and
an electrical contact that the user can connect to an emergency stop or interlock
Below, the main characteristics and requirements for the classification system from 2002
are listed, along with typical required warning labels. Additionally, classes 2 and higher
must have the triangular warning label shown here and other labels are required in specific
cases indicating laser emission, laser apertures, skin hazards, and invisible wavelengths
Class 1
A class 1 laser is safe under all conditions of normal use. This means the maximum
permissible exposure (MPE) cannot be exceeded. This class includes high-power lasers
within an enclosure that prevents exposure to the radiation and that cannot be opened
without shutting down the laser. For example, a continuous laser at 600 nm can emit up to
0.39 mW, but for shorter wavelengths, the maximum emission is lower because of the
potential of those wavelengths to generate photochemical damage. The maximum
emission is also related to the pulse duration in the case of pulsed lasers and the degree of
spatial coherence.
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