LASER SAFETY
Introduction
The term LASER is an acronym for Light Amplification by
Stimulated Emission of Radiation.
Laser emits electromagnetic radiation by the process of
optical amplification based on stimulated emission of
photons.
Characteristics of Lasers
• Monochromatic – laser consist of mostly single wavelength
rather than different wavelengths.
• Coherent - wavelengths in a laser beam are in phase.
The wave crests and troughs are parallel to each other.
• Collimated – very narrow, travel in the same direction.
As a result of these properties intense power is produced
at a small point of concentration.
Components of a Laser
A laser consists of
• An optical cavity,
• A pumping system (energy source) and
• An appropriate lasing medium.
Types of Lasers
Lasers can be classified by the type of lasing material in the
optical cavity.
• Solid state lasers make use of a crystalline lasing material.
e.g., ruby or neodymium-YAG (yttrium aluminium garnet)
lasers.
• Gas lasers uses pure gas or mixture of gases. e.g., carbon
dioxide and helium-neon.
Types of Lasers
• Semiconductor/diode lasers employ n-type and p-type
semiconducting element materials.
• Liquid/dye lasers employ organic dye in a liquid solution or
suspension as lasing media.
• Excimer lasers (the name is derived from the terms excited
and dimers) use gases such as chlorine and fluorine mixed
with inert gases such as argon, krypton or xenon.
Laser beam exposure
Exposure to laser beam can occur by the following means
• Direct viewing of the beam
• Specular reflection – from a shiny surface
• Diffuse reflection – from an irregular surface
Classification of Lasers
On the basis of the damaging effects on the eyes and skin
lasers are classified into the following types:
• Class 1
• Class 1C
• Class 1M
• Class 2
• Class 2M
• Class 3R
• Class 3B
• Class 4
Class 1 Laser System
• Is usually not capable of producing damaging radiation
levels during normal operation.
• Class 1 laser systems are exempted from control
measures.
• Lasers used in laser printers and compact disc players are
examples.
Class 1C Laser System
• Class 1C lasers are laser products used on the skin or
internal body tissues for medical procedures.
Class 1M Laser System
• Is not capable of producing hazardous exposure conditions
during normal operation, except when the beam is viewed
with an optical instrument.
• Control measures are not recommended but potentially
hazardous optically aided viewing to be avoided.
• Lasers used for fiber optic communication system comes
under this classification.
Class 2 Laser System
• Because of the human aversion response, these lasers do
not normally present a hazard, but may be a potential
hazard if viewed directly for a long time.
• Laser pointers are examples of lasers coming under this
classification.
Class 2 Laser System
Class 2M Laser System
• Aversion response of eyes offer protection to the eyes.
• Class 2M can be potentially hazardous when viewed with
optical aids.
• Lasers used in level and orientation instruments
in civil work are examples of Class 2M lasers.
Class 3R Laser System (medium power)
• Potentially hazardous under direct and specular
reflection viewing condition if the eye is appropriately
focused and stable, but the probability of injury is small.
• Is not a fire hazard or diffuse-reflection hazard.
• Some laser pointers are classified as Class 3R
lasers.
Class 3B Laser System (medium power)
• Can be hazardous under direct and specular reflection
viewing conditions.
• Is normally not a diffuse reflection or fire hazard.
• Class 3B laser systems are used in physiotherapy
treatments and research work.
Class 4 Laser system (high-power)
• Is a hazard to the eye and skin from the direct beam.
• May pose a diffuse reflection hazard.
• Can cause fire.
• May produce laser generated air contaminants and
hazardous plasma radiation.
• Class 4 lasers are used in displays and cutting of metals.
Biological effects of Laser Beam
Lasers can cause damage in biological tissues, both to the
eye and to the skin, by the following mechanisms.
• Thermal damage - burns occur when tissues are heated to
the point where denaturation of proteins occurs.
• Photochemical damage - where light triggers chemical
reactions in tissue.
Biological effects of Laser Beam
Eye injury
• The ocular focus region is a range of wavelengths from
0.4-1.4 µm, which is focused by the eye’s components
with a power of approximately 100,000 times.
• This portion of the spectrum reaches the retina and are
absorbed there resulting in injury.
• All rays outside the ocular region are absorbed by the outer
components of the eyes.
Biological effects of Laser Beam
Eye injury
• Moderate and high power lasers in the visible to near
infrared range (0.4 -1.4 µm) will cause burns on the retina
resulting in permanent blind spots.
• Laser radiation with wavelengths less than 0.4 µm and
greater than 1.4 µm are largely absorbed by the cornea
and lens, leading to the development of cataracts or burn
injuries.
Absorption of electromagnetic radiation in the eye
Near Ultraviolet(UV)
Visible and Near IR
Far UV and Far Infrared (IR)
Optic nerves
Retina
Lens
Cornea
Biological effects of Laser Beam
Skin injury
Excessive exposure to UV light from lasers can cause effects
similar to sunburn, while visible and infrared rays can cause
thermal damage.
• UV-A (0.315 µm-0.400 µm) can cause hyper pigmentation
and erythema.
• UV-B range (0.280 µm - 0.315 µm) is most injurious to
skin. Can cause radiation carcinogenesis.
• UV-C (0.200 µm-0.280 µm) is less harmful to human skin.
Causes of laser accidents
• Eye exposure during alignment
• Misaligned optics
• Non use of laser safety glasses
• Equipment malfunction
• Improper methods of handling high voltage
• Unauthorised operation
• Lack of protection for non-beam hazards
Control measures for Class 3B and Class 4 Lasers
• To be operated by authorised personnel only.
• Access to the area for visitors to be limited, by the
provision of partitions.
• Visitors not to be allowed when the laser is in operation.
• Any potentially hazardous beam to be terminated in a beam
stop of an appropriate material.
Control measures for Class 3B and Class 4 Lasers
• Warning sign to be posted at the entrance.
• Warning lights to be provided outside the laser room to warn
visitors when the laser is in operation.
Control measures for Class 3B and Class 4 Lasers
• Materials that can cause specular reflection must not be
kept in the laboratory.
• Laser safety glasses must be used if the permissible
exposure limits for the laser are exceeded.
Control measures for Class 3B and Class 4 Lasers
• Wherever possible the beam path must be enclosed. Use
fire resistant materials for enclosing Class 4 laser beam
path.
• All windows and doors in the laser room to be made
opaque.
• The laser system must be disabled ( e.g., removal of
the key) after use to prevent unauthorised use.
Control measures for Class 3B and Class 4 Lasers
A screen or curtain must be used to prevent exposure to the
laser beam at the entrance of the laser room.
Control measures for Class 3B and Class 4 Lasers
Secure optical components to the table to prevent stray
reflections from misaligned optics.
Control measures for Class 3B and Class 4 Lasers
• Users must never view the beam at the level of the
horizontal plane where they are passing.
• Watches and jewelry must not be used in the
laboratory.
• Alignment of beams and optical components must be
performed at a reduced beam power whenever possible.
• Fire extinguishers must be at an easily accessible location
in labs using Class 4 lasers. Keep flammable materials away
from open beams.
Factors in determining appropriate eyewear
• Wavelength of the laser output
• Potential for multi wavelength operation
• Optical density of eyewear at laser output wavelength
• Visible light transmission requirement
• Peripheral vision requirement
• Comfort and fit
Non-beam laser hazards
Non-beam hazards are also associated with use of laser
systems.
• Lasers use high voltages which can be a hazard during
normal operation and maintenance.
• The laser system must be properly grounded.
• Electrical switches must be locked and tagged while
servicing electrical equipment to prevent inadvertent
energisation.
Non-beam laser hazards
• Capacitors can contain dangerous charge even after
disconnecting from the main power. They must be safely
discharged by grounding before maintenance.
• Electrical equipment must be installed a few inches
above the floor to prevent contact with water in case of
flooding.
• Organic dyes used must be labelled and Material Safety
Data Sheet for the same to be referred before use.
• High-pressure arc lamps and filament lamps shall be
enclosed to contain lamp explosion.
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