An introduction to

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An introduction to LASER PHYSICS and SAFETY
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• What is a Laser?
• How is Laser light produced?
• What are the components of a laser system?
• What makes laser light special?

• How does laser light interact with tissue?
• What are the safety issues?

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Laser light is a form of Electromagnetic
Radiation
GentleYAG (1064)
Smoothbeam (1450)
GenlteLASE family (755)
Vbeam (595)
400
500
600
700
1,000
10,000
Nanometers
Visible Light
Invisible Light
Ultraviolet
Microwave
X-Ray
TV and FM Radio
AM Radio
Cosmic
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The word laser is an acronymit
stands for Light Amplification
by Stimulated Emission of Radiation
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How is laser light produced?
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Atoms of any substance are made up of electrons,
protons and neutrons.
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Electrons are usually in a resting stage
when they absorb a photon, they are raised to an
excited stage.
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Once raised to an excitedstage, the
electron naturally tends to return to its
restingstage, and does so by emitting a
photon (similar to the one absorbed) this is
called spontaneous emission.
Spontaneous emission
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If when in its excited stage the electron
absorbs a second photon, it then needs to emit
two photons (similar to the ones absorbed) this
is called stimulated emission.
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A laser beam is generated by amplification, which
is stimulated emission repeated innumerable times.
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What Are The Components Of A Laser system?
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There are four basic components to every laser
Lasing medium Optical cavity Power
source Delivery system
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Laser diagram
Laser
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The lasing medium (located inside the optical
cavity) is the substance that produces the
laser beam.
This could be a GAS (argon, krypton, CO2), a
SOLID (ruby crystals, alexandrite crystals),
or a LIQUID (dye). The lasing medium determines
the wavelength of the laser.
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The power source is used to stimulate the lasing
medium to produce the laser beam.
Power sources include Electricity
Flashlamps Other lasers
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The delivery system modifies the laser
beam and brings it from the optical cavity to the
patient.
Delivery systems include Articulated arms
Optical fibers Micromanipulators Focusing
handpieces Lenses
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There are two types of lasers
Laser beam
Lasing medium
Continuous wave lasers (pulse duration is not
relevant)
Laser beam
Lasing medium
Pulsed lasers (pulse duration is a variable)
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What Makes Laser Light Special?
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Laser light has three unique properties
It is monochromatic It is coherent It is
collimated
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Laser light is monochromatic the wavelength
approaches unity.
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Laser light is coherent the light waves are
spatially and temporally in phase.
Laser light
Regular white light
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Laser light is collimated the light waves are
parallel and not divergent.
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How does laser light interact with tissue?
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Selective photothermolysis a concept developed
by Rox Anderson in 1983
States that laser light of a specific
wavelength can destroy a target containing the
adequate chromophore without damaging the
surrounding tissue. This is possible if the
thermal relaxation time of the target is longer
than the duration of the laser pulse.
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What Are Laser Parameters?
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There are four basic laser parameters
Wavelength Pulse duration Spot size
Fluence
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Absorption is necessary for effect on tissue.
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Wavelength chosen partly based on the absorption
curve of the targeted chromophore.

• Chromophores of interest in dermatology are
• Haemoglobin
• Water
• Melanin

Wavelength (nm)
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Wavelength

• It is determined by the lasing medium.
• It is measured in nanometers.
• As absorption decreases the depth of penetration
  increases

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Pulse duration (pulse width) refers to the
duration of each laser pulse.

• In order to get a selective effect on the target
  only, the pulse duration should be matched to the
  thermal relaxation time of the target
• Smaller targets require smaller pulse durations

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Spot size refers to the diameter of the beam
emitted. A larger spot size induces deeper
penetration
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Distance gauges are used to set the required spot
size at the tissue surface
Focal Plane
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The fluence measures the rate of energy delivery
per unit area.
It is measured in Joules per cm2. As the
fluence increases, so does the destructive force
of the laser. The relationship between fluence
and spot size is important.
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In summary we choose parameters

• To achieve the correct depth of penetration for
  our target
• To selectively target the chormophore of interest
• To provide enough energy over an appropriate time
  to have a selective photothermolysis effect

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Laser Safety As It Relates To Laser-Tissue
Interaction

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Hazards
Lasers are classified in four broad
groups Class I No known biological
hazardClass II Chronic viewing hazard
onlyClass III Direct viewing hazardClass IV
Direct and reflected hazard
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Window protection
All windows in a laser treatment roomshould be
protected from beam transmission and covered with
opaque material. There should be no mirrors in
the treatment room.
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Eye protection is a MUST!
AORN Recommended Practice IIEyes of patients
and health care workersshould be protected from
laser beams. Interpretive Statement
ILaser-safe eye protection with appropriate
wavelength and optical density should be worn by
all health care workers and all patients and
labeled to protect against improper use.
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Laser eye penetration
CO2 Erbium Diode
Corneal absorption
Pulsed dye NdYAGAlexandrite
Retinal absorption
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Different eyewear for different wavelengths!
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Laser signs
All doors to a laser treatment room are to be
closed and have a laser specific danger sign
along with a pair of laser eyewear prominently
displayed.
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Fire hazard be on the lookout for flammable or
combustible materials!
Anesthetics Prep solutions Drying
agents Ointments Plastics Resins Hair
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Plume issues
Thermal destruction of tissue creates smoke
byproduct. Plume can contain toxic gases and
vapors, dead and live cellular materials
including blood fragments and viruses. A laser
protective mask (0.1µ) should be used to decrease
inhalation of particulate matter when
appropriate
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Plume issues (ctd.)
General room ventilation is not sufficient to
capture contaminants. Smoke evacuators should
have high efficiency in airborne particle
reduction. HEPA filter or equivalent is
recommended for trapping particulates.
Generally, the use of smoke evacuators is more
effective than room suction systems.
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A laser should always be in standby mode unless
an operator is ready to use it.
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REMEMBER

• Laser sign
• Doors closed
• Windows covered
• Eye protection
• Standby mode
• Fire
• Plume
• Electrical safety