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Laser light is monochromatic, directional and coherent. These three properties make it more of a hazard than ... Ergonomics Considerations. Protective Measures ... – PowerPoint PPT presentation

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  • For more information refer to the department
    Laser Safety Procedure
  • http//
  • l

Definition Properties of Laser Light
  • Acronym For

Properties Of Laser Light
  • Laser light is monochromatic, directional and
  • These three properties make it more of a hazard
    than ordinary light. 
  • Laser light can deposit a great deal of energy
    within a very small area

Properties Of Laser Light
  • Monochromatic
  • The light emitted from a laser is monochromatic,
    it is of one wavelength (color). 
  • In contrast, ordinary white light is a
    combination of many different wavelengths

Properties Of Laser Light
  • Directional
  • Lasers emit light that is highly directional. 
  • It is emitted as a narrow beam in a specific
  • Ordinary light (sun, light bulb, a candle), is
    emitted in many directions away from the source

Properties Of Laser Light
  • Coherent
  • The light from a laser is coherent
  • The wavelengths of the laser light are in phase
    in space and time

The Electromagnetic Spectrum
  • The electromagnetic spectrum consists of the
    complete range of frequencies from radio waves to
    gamma rays 
  • All electromagnetic radiation consists of
    photons - individual quantum packets of energy 
  • Light consists of photons, each with discrete
    quantum of energy proportional to their
  • Light with a shorter wavelength is consisted of
    higher energy photons

The Electromagnetic Spectrum
The Electromagnetic Spectrum
  • The portion of the electromagnetic spectrum where
    lasers operate
  • Infrared near infrared 750 nm - 3000 nm far
    infrared 3000 nm - 1 mm
  • Visible 400 nm - 750 nm
  • Ultraviolet 100 nm - 400 nm.

How Does Laser Work?
  • The Lasing Medium
  • A substance that when excited by energy emits
    light in all directions. Can be a gas, liquid, or
    semi-conducting material.
  • The Excitation Mechanism or Energy Pump
  • The excitation mechanism of a laser is the source
    of energy used to excite the lasing medium. 
  • Excitation mechanisms typically used are
    electricity, flash tubes, lamps, or the energy
    from another laser.

How Does Laser Work?
  • The Optical Cavity
  • The optical cavity is used to reflect light from
    the lasing medium back into itself.  It typically
    consists of two mirrors, one at each end of the
    lasing medium.  As the light is bounced between
    the two mirrors, it increases in strength,
    resulting in amplification of the energy in the
    form of light. 
  • The output coupler of a laser is usually a
    partially transparent mirror on one end of the
    lasing medium that allows some of the light to
    leave the optical cavity to be used for the
    production of the laser beam.

How it Works?
  • The lasing medium emits photons in specific
    spectral lines when excited by an energy source. 
  • The wavelength is determined by the different
    energy states of the material.  Most atoms in a
    medium are in the ground state. Small percentage
    will exist at higher energies. These higher
    energy states are unstable and the electrons will
    release the excess energy as photons and will
    return to the ground state.
  • The energy is supplied to the laser medium by the
    energy pumping system is stored in the form of
    electrons trapped in the metastable energy
    levels. Pumping must produce more atoms in the
    metastable state than the ground state before
    laser action can take place.

How it Works?
  • When this is achieved, the spontaneous decay of a
    few electrons from the metastable energy level to
    a lower energy level, starts a chain
    reaction. The photons emitted spontaneously will
    hit other atoms and stimulate their electrons to
    make the transition from the metastable energy
    level to lower energy levels - emitting photons
    of precisely the same wavelength, phase, and
  • This action occurs in the optical cavity.  When
    the photons that decay in the direction of the
    mirrors reach the end of the laser material, they
    are reflected back into the material where the
    chain reaction continues and the number of
    photons increase.  When the photons arrive at the
    partially-reflecting mirror, only a portion will
    be reflected back into the cavity and the rest
    will emerge as a laser beam.

Laser Components
Types of Lasers by kind of Lasing Media
  • Lasers are often described by the kind of lasing
    medium they use - solid state, gas, excimer, dye,
    or semiconductor.
  • Solid state lasers have lasing material
    distributed in a solid matrix, e.g., the ruby or
    neodymium-YAG (yttrium aluminum garnet) lasers.
    The neodymium-YAG laser emits infrared light at
    1.064 micrometers.
  • Gas lasers (helium and helium-neon, HeNe, are
    the most common gas lasers) have a primary output
    of a visible red light. CO2 lasers emit energy in
    the far-infrared, 10.6 micrometers, and are used
    for cutting hard materials.
  • Excimer lasers (the name is derived from the
    terms excited and dimers) use reactive gases such
    as chlorine and fluorine mixed with inert gases
    such as argon, krypton, or xenon. When
    electrically stimulated, a pseudomolecule or
    dimer is produced and when lased, produces light
    in the ultraviolet range.

Types of Lasers by kind of Lasing Media
  • Dye lasers use complex organic dyes like
    rhodamine 6G in liquid solution or suspension as
    lasing media. They are tunable over a broad range
    of wavelengths.
  • Semiconductor lasers sometimes called diode
    lasers, are not solid-state lasers. These
    electronic devices are generally very small and
    use low power. They may be built into larger
    arrays, e.g., the writing source in some laser
    printers or compact disk players.

Types of Lasers by Duration of LASER Emission
  • Lasers are also characterized by the duration of
    laser emission, continuous wave or pulsed laser. 
  • Q-Switched laser is a pulsed laser which contains
    a shutter-like device that does not allow
    emission of laser light until opened.   Energy is
    built-up in a Q-Switched laser and released by
    opening the device to produce a single, intense
    laser pulse.
  • Continuous Wave (CW) lasers operate with a stable
    average beam power. In most higher power systems,
    one is able to adjust the power. In low power gas
    lasers, such as HeNe, the power level is fixed by
    design and performance usually degrades with long
    term use.

Types of Lasers by Duration of LASER Emission
  • Single Pulsed (normal mode) lasers generally have
    pulse durations of a few hundred microseconds to
    a few milliseconds. This mode of operation is
    sometimes referred to as long pulse or normal
  • Single Pulsed Q-Switched lasers are the result
    of an intracavity delay (Q-switch cell) which
    allows the laser media to store a maximum of
    potential energy. Then, under optimum gain
    conditions, emission occurs in single pulses
    typically of 10(-8) second time domain. These
    pulses will have high peak powers often in the
    range from 10(6) to 10(9) Watts peak.
  • Repetitively Pulsed or scanning lasers generally
    involve the operation of pulsed laser performance
    operating at a fixed (or variable) pulse rates
    which may range from a few pulses per second to
    as high as 20,000 pulses per second. The
    direction of a CW laser can be scanned rapidly
    using optical scanning systems to produce the
    equivalent of a repetitively pulsed output at a
    given location.
  • .

Types of Lasers by Duration of LASER Emission
  • Mode Locked lasers operate as a result of the
    resonant modes of the optical cavity which can
    effect the characteristics of the output beam.
    When the phases of different frequency modes are
    synchronized, i.e., "locked together," the
    different modes will interfere with one another
  • The result is a laser output which is observed
    as regularly spaced pulsations. Lasers operating
    in this mode-locked fashion, usually produce
    spaced pulses, each having a duration of 10(-15)
    (femto) to 10(-12) (pico) sec. A mode-locked
    laser can deliver extremely high peak powers
    often in the range from 10(12) Watts peak

Classifications of Lasers
  • Lasers are classified with respect to their
    hazards based on power, wavelength, and pulse
  • A classification label will be found on the laser
    housing.  This label provides important
    information on the hazard of the laser. 
  • Classes of Lasers adopted from ANSI Z-136.1-2000

Classifications of Lasers- Class 1
  • Not capable of emitting in excess of the Class 1
    Accessible Emission Limit (AEL) (Note AEL's vary
    by laser wavelength and pulse duration)
  • Most lasers in this class are lasers which are in
    an enclosure which prohibits or limits access to
    the laser radiation.
  • Not capable of producing damage to the eye
    (unless disassembled).

Classifications of Lasers- Class 2
  • Continues wave and repetitive-pulse lasers in the
    visible region of the spectrum (0.4 to 0.7 mm)
    which can emit accessible radiant energy
    exceeding the Class 1 AEL for the maximum
    duration inherent in the laser, but not exceeding
    the Class 1 AEL for any pulse duration lt 0.25s
    (the time estimated to blink or look away) and
    not exceeding an average radiant power of 1 mW.
  • The output of the laser is not intended to be
  • An example of a Class 2a laser is a supermarket
    point-of-sale scanner.

Classifications of Lasers- Class 3a
  • Have output between 1 and 5 times the Class 1 AEL
    for wavelengths shorter than 0.4 mm or longer
    than 0.7 mm, or less than 5 times the Class 2 AEL
    for wavelengths between 0.4 mm and 0.7 mm.
  • Is only a hazard if collected and focused in the
  • Most laser pointers are 3a lasers.

Classifications of Lasers- Class 3b
  • Ultraviolet and infrared lasers and laser systems
    that can emit accessible radiant power in excess
    of the Class 3a AEL during any emission duration
    within the maximum duration inherent in design of
    the laser or system, but that - cannot emit an
    average radiant power in excess of 0.5 W for
    greater than or equal to 0.25 s or cannot produce
    a radiant energy greater than 0.125 J within an
    exposure time gt 0.25 s.
  • Visible or near-infrared lasers or systems that
    emit in excess of the 3a AEL but that cannot emit
    an average radiant power in excess of 0.5 W for
    greater than or equal to 0.25 s and cannot
    produce a radiant energy greater than 0.03 Ca J
    per pulse. (Ca is a correction factor that
    increases the maximum permissible exposure values
    in the near infrared spectral band based upon
    reduced absorption propertied of melanin pigment
    granules found in skin and in the retinal pigment
  • Is a hazard if the direct or reflected beam is

Classifications of Lasers- Class 4
  • Limits exceed Class 3b limits.
  • Direct and reflected exposure can cause both eye
    and skin injury.
  • Class 4 lasers are also a fire hazard.

Biological Beam Hazard
  • The damage is principally due to temperature
    effects, the critical organs are the eye and the
  • The components of the eye most susceptible to
    laser damage are the cornea, retina, and lens

Summary of Biological Effects of Light
Eye Injury
  • Light causes biological damage through
    temperature effects due to absorbed energy and
    through photochemical reactions.  The chief mode
    of damage depends on the wavelength of the light
    and on the tissue being exposed
  • A laser beam of sufficient power can produce
    retinal intensities at magnitudes that are
    greater than conventional light sources, and even
    larger than those produced when directly viewing
    the sun. Permanent blindness can be the result
  • Laser irradiation of the eye may cause damage to
    the cornea, lens, or retina, depending on the
    wavelength of the light and the energy absorption
    characteristics of the ocular tissues.

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Light Induced Biological Damage
  • The potential location of injury in the eye is
    directly related to the wavelength of the laser
    radiation entering the eye
  • Near Ultraviolet Wavelengths (UVA) 315 - 400 nm
  • Most of the radiation is absorbed in the lens of
    the eye.
  • The effects are delayed and do not occur for many
    years (e.g. cataracts).
  • Far Ultraviolet (UVB) 280 - 315 nm, (UVC) 100 -
    280 nm
  • Most of the radiation is absorbed in the cornea.
  • Keratocojunctivitis (snow blindness/welder's
    flash) will result if sufficiently high doses are

Light Induced Biological Damage
  • Visible (400 -760 nm) and Near Infrared (760 -
    1400 nm)
  • Most of the radiation is transmitted to the
    retina. ()
  • Overexposure may cause flash blindness or retinal
    burns and lesions.
  • Far Infrared (1400 nm - 1 mm)
  • Most of the radiation is transmitted to the
  • Overexposure to these wavelengths will cause
    corneal burns.
  • () Laser retinal injury can be severe because of
    the focal magnification (optical gain) of the eye
    which is approximately 100,000 times. This means
    that an irradiance of 1 mW/cm2 entering the eye
    will be effectively increased to 100 W/cm2 when
    it reaches the retina.

Light Induced Biological Damage
  • For pulsed lasers, the pulse duration also
    effects the potential for eye injury. Pulses less
    than 1 ms in duration focused on the retina can
    cause an acoustical transient, resulting in
    substantial damage and bleeding in addition to
    the expected thermal injury. Many pulsed lasers
    now have pulse duration less than 1 pico-second.
  • The ANSI Z136.1 standard defines the Maximum
    Permissible Exposure (MPE) that the eye can
    receive without expecting an eye injury (under
    specific exposure conditions). If the MPE is
    exceeded, the probability that an eye injury can
    result increases dramatically.

Light Induced Biological Damage
  • Thermal burns (lesions) in the eye are caused
    when the heat loading of the retina can not be
    regulated. Secondary bleeding may occur as a
    result of burns which damage blood vessels. This
    bleeding can obscure vision well beyond the area
    of the lesion.
  • Although the retina can repair minor damage,
    major injury to the macular region of the retina
    may result in temporary or permanent loss of
    vision or blindness.
  • Photochemical injury to the cornea by ultraviolet
    exposure may result in photokeratoconjunctivitis
    (often called welders flash or snow blindness).
    This painful condition may last for several days
    is long term.
  • UV exposure can cause cataract formation in the

Light Induced Biological Damage
  • The duration of exposure also plays a role in eye
  • If the laser is a visible wavelength (400 to 700
    nm), the beam power is less than 1.0 mW and the
    exposure time is less than 0.25 second (the human
    aversion response time), no injury to the retina
    would be expected to result from an intrabeam
    exposure. Class 1, 2a and 2 lasers fall into this
    category and do not normally present a retinal
  • Intrabeam or specular reflection viewing of Class
    3a, 3b, or 4 lasers and diffuse reflections from
    Class 4 lasers may cause an injury before the
    aversion response can protect the eye.

Skin Hazard
  • The most likely skin surfaces to be exposed to
    the beam are the hands, head, or arms.
  • Laser effects on tissue depend on - the power
    density of the incident beam, absorption of
    tissues at the incident wavelength, the time beam
    is held on tissue, and the effects on blood
    circulation and heat conduction in the effected

Skin Hazard
  • Immediate Effects
  • The immediate effect of exposure to laser light
    above the biological damage threshold is normally
    burning of the tissue.  Injury to the skin can
    result either from thermal injury following
    temperature elevation in skin tissues or from a
    photochemical effect (e.g., "sunburn") from
    excessive levels of ultraviolet radiation.
  • Delayed Effects
  • Only optical radiation in the ultraviolet region
    of the spectrum has been shown to cause
    long-term, delayed effects. These effects are
    accelerated skin aging and skin cancer.  At
    present, laser safety standards for exposure of
    the skin attempt to take these adverse effects
    into account.

Non-Beam Hazards
  • Many of these non-beam related hazards can be
    far more dangerous than the beam itself.
  • Electrical Hazard
  • The use of large power supplies and repetitively
    pulsed lasers, present a great potential for
    electric shock.  Shocks usually happen when the
    equipment is not properly grounded or has a large
    capacitor bank that was not discharged.
    According to the ANSI Z136.1, the following
    potential problems have frequently been
    identified during laser facility audits
  • Uncovered electrical terminals.
  • Improperly insulated electrical terminals.
  • Hidden "power up" warning lights.
  • Lack of training in current cardiopulmonary
    resuscitation practices, or
  • lack of refresher training.
  • "Buddy system" not being practiced during
    maintenance and service.
  • Non-earth-grounded or improperly grounded laser
  • Non-adherence to the lock-out procedures
  • Excessive wires and cables on floor that create
    fall or slip hazards

Non-Beam Hazards
  • Explosion Hazard
  • With the use of high-pressure arc lamps,
    filament lamps, and capacitor banks in laser
    equipment, there is a potential for explosion
    hazards.  These items should be enclosed in
    housings that can withstand the high pressure
    resulting from exploding components.
  • Compressed Gasses
  • Many lasers are using hazardous gases such as
    chlorine, fluorine, hydrogen chloride, and
    hydrogen fluoride.  Referring to ANSI Z136.1,
    typical safety problems arise in the use of
    compressed gasses
  • Inability to protect open cylinders (regulator
    disconnected) from atmosphere and contaminants.
  • No remote shutoff valve or provisions for purging
    gas before disconnect or reconnect.
  • Hazardous gas cylinders not maintained in
    exhausted enclosures.
  • Gases of different hazard (toxics, corrosives,
    flammable, oxidizers, and cryogenics) not stored

Non-Beam Hazards
  • Laser Dyes and Solvents
  • Dyes are used in some lasers as a lasing
    medium. These dyes are complex organic compounds
    that are mixed in solution with certain
    solvents.  Some dyes are highly toxic or
    carcinogenic, and great care must be taken when
    handling them, preparing solutions, and operating
    lasers that contain these dyes.  A Material
    Safety Data Sheet must be made available to
    anyone working with these dyes.
  • Noise
  • Some lasers, such as the Excimer, create an
    intensity of noise that may require controls to
    be instituted.  The Health and Safety Office
    should be consulted if there are concerns about

Non-Beam Hazards
  • Fire Hazards
  • There is a great potential for a fire hazard with
    the use of Class IV lasers.  Fires can occur when
    a Class IV laser is enclosed in a material that
    is exposed to irradiances greater than 10 W/cm2
    or beam powers exceeding 0.5 W.  Fire resistant
    materials should be used in this situation.
  • Barriers such as black photographic cloth are
    used in a wide variety of applications for the
    purpose of containing the beam.  These materials
    should not be used as the primary barrier for a
    high-powered Class IV system. Beams of sufficient
    energy will burn this material quickly, causing
    smoke, fire, and breach of the barrier. The use
    of beam blocks and beam stops is highly
    encouraged in this situation.

Non-Beam Hazards
  • X-Ray Radiation Hazards
  • X-rays may be generated by electronic components
    of the laser system (e.g., high-voltage vacuum
    tubes and from laser-metal induced plasmas).
  • Some lasers contain RF excited components, such
    as plasma tubes and Q-switches. 
  • Other Hazards
  • Mechanical Hazards Associated with Robotics
  • Limited Work Space Dangers
  • Ergonomics Considerations

Protective Measures
  • Protective measures are devised to reduce the
    possibility of exposure of the eye and skin to
    hazardous levels of laser radiation. And reduce
    other hazards associated with laser devices
    during operation and maintenance.
  • Engineering controls will be the "first line of
    defense" when it comes to protection from laser
    radiation and its ancillary hazards.
  • Enclosure of the beam path is the preferred
    method of control since the enclosure will
    isolate or minimize the hazard.
  • If engineering controls are impractical or
    inadequate, administrative and procedural
    controls and personal protective equipment will
    be used

Summary of Engineering Controls
Legend R- Normally required O- Optional
X-No requirements NC- No further controls
required LSO- Laser Safety Officer
Engineering Controls
Summary of Administrative Controls
Legend R- Normally required O- Optional
X-No requirements NC- No further controls
required LSO- Laser Safety Officer
Laser Safety Glasses
  • When all other protective measures fail, wearing
    proper laser safety glasses for the wavelength
    and power of the laser will protect your eyes. 
  • Wear these glasses whenever there is a
    possibility of exposure to laser light above the
  • Different protective lenses should be used for
    different wavelengths
  • The first thing to take into account when
    choosing safety glasses is WAVELENGTH

Laser Safety Glasses
  • The Optical Density must also be taken into
    account even if the proper protection for a
    certain wavelength was chosen, lenses do not
    filter out all of the light that incident upon
    them, and all lenses are not rated the same. This
    is where (OD) comes into play. The OD is defined
    by the ANSI Z136.1 as the logarithm to the base
    ten of the reciprocal of the transmittance
  • Dl - log10 tl (where tl is the transmittance)
  • Both the wavelength and the OD must be labeled on
    either the temple for glasses, or on the frame,
    for goggles.

Laser Safety Glasses
  • In certain applications, as in the use of
    powerful Class IV lasers, certain protective
    lenses are not meant as a permanent protective
    shield. For example, in the use of Class IV CO2
    lasers _at_ 10,600 nm, the protective lens only
    provides sufficient protection to allow immediate
    movement away from the beam. If the operator
    remains in the path of the beam, the beam will
    burn through the lens very quickly.

Laser Safety Glasses
  • Other considerations when Selecting Eye
  • High Visual Transmittance
  • Resistance to Fogging
  • Good Peripheral Vision
  • Side Shield and Vent Ports
  • Optical Correction
  • Resistance to UV Degradation
  • Comfort

Laser Safety Glasses
  • All protective eyewear must be inspected before
    each use to ensure that it will provide adequate
  • Prior to using laser safety glasses
  • Check that the eyewear will provide the proper
    protection for the wavelength of concern
  • The lenses must be inspected for any deep
    scratches or grooves. If any are found, the
    eyewear is not to be used
  • The frame should also be inspected at this time.
  • Check for missing or loose temple screws and
    ensure that the glasses comfortably fit your

  • The laser lab Principal Investigator has the
    Laser Safety Officer responsibilities for their
  • The laser worker is one who operates or works in
    proximity to Class 3b or Class 4 lasers. He/she
    has the following responsibilities
  • To participate Laser Safety training
  • To be familiar with all operational procedures
    and specific safety hazards of the Class 3b or
    Class 4 laser/laser systems that he/she will
  • To operate Class 3b and Class 4 laser/laser
    systems safely and in a manner consistent with
    safe laser practices, requirements and written
  • To operate Class 3b and Class 4 laser/laser
    systems only under the conditions authorized by
    the laser principal investigator
  • To report all unsafe conditions, known or
    suspected accidents to the principal
  • To report to the laser principal investigator any
    medical conditions that could cause him/her to be
    at increased risk for chronic exposure