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					An introduction to
  LASER
PHYSICS and
  SAFETY
• 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?
                         Laser light is a form of
                       Electromagnetic Radiation:




                                      GentleYAG


                                                     Smoothbeam
         Vbeam (595)



                       family (755)
                       GenlteLASE




                                      (1064)


                                                     (1450)
400 500 600 700                                   1,000               10,000
  Visible Light                         Nanometers                Invisible Light
     Ultraviolet                                                   Microwave
    X-Ray                                                         TV and FM Radio
Cosmic                                                                  AM Radio
The word laser is an acronym…it
stands for:

    Light
    Amplification by
    Stimulated
    Emission of
    Radiation
How is laser light
  produced?
    Atoms of any substance are made up of
       electrons, protons and neutrons.

Nucleus:
protons &
neutrons




Electrons in Orbit
             Resting stage         Excited stage



 Electrons are usually in a “resting” stage;
when they absorb a photon, they are raised to
          an “excited” stage.
          Once raised
  to an “excited”stage,
 the electron naturally
tends to return to its
“resting”stage, and
does so by emitting a     Spontaneous emission
photon (similar to the
one absorbed): this is
called spontaneous
        emission.
    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.




                    Stimulated emission
A laser beam is generated by
   amplification, which is
stimulated emission repeated
     innumerable times.




              Stimulated emission
 What Are The
Components Of A
 Laser system?
There are four basic components
         to every laser:
      •Lasing medium
      •Optical cavity
      •Power source
      •Delivery system
              Laser diagram:

                Optical cavity
                                        Laser beam
              Lasing medium




 Totally          Power           Partially
reflective        source         reflective
  mirror                           mirror




             Laser
                 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.
 The power source is used to
stimulate the lasing medium to
   produce the laser beam.

    Power sources include:
     • Electricity
     • Flashlamps
     • Other lasers
    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
                    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)
What Makes
Laser Light
 Special?
Laser light has three unique
         properties:

    •It is monochromatic
    •It is coherent
    •It is collimated
Laser light is monochromatic: the wavelength
               approaches unity.




  Ordinary Light     Laser Light
     Laser light is coherent: the light waves are
        spatially and temporally in phase.


Laser light             Regular “white” light
         Laser light is collimated: the light
        waves are parallel and not divergent.



Laser
How does laser light
interact with tissue?
               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.
What Are Laser
 Parameters?
There are four basic laser
      parameters:

  • Wavelength
  • Pulse duration
  • Spot size
  • Fluence
     Absorption is necessary for
     effect on tissue.




Reflection Scattering Transmission Absorption
             Wavelength: chosen partly based on the
                    absorption curve of the targeted
                                   chromophore.
                                                    Chromophores of
ABSORPTION
                                                    interest in
                                                    dermatology are:
                   Oxyhemoglobin
                                                    •Haemoglobin
                                                    •Water
                                                    •Melanin
                                    Melanin



             400     500     600      700     800


                           Wavelength (nm)
                              Wavelength:



•   It is determined by the
    lasing medium.
•   It is measured in
    nanometers.
•   As absorption
    decreases the depth of
    penetration increases
                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
Spot size refers to the diameter of the
  beam emitted. A larger spot size
     induces deeper penetration
       Distance gauges are used to set the
           required spot size at the tissue
                        surface   Focal
                                  Plane

Laser
focusing                                  Focal
lens                                      spot




                  Focal length
         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.
        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
Laser Safety
As It Relates
  To Laser-
   Tissue
 Interaction
                      Hazards:

  Lasers are classified in four broad groups:

Class I     No known biological hazard
Class II    Chronic viewing hazard only
Class III   Direct viewing hazard
Class IV    Direct and reflected hazard
      Window protection:

All windows in a laser treatment
             room
 should be protected from beam
 transmission and covered with
        opaque material.
There should be no mirrors in the
        treatment room.
                            Eye protection is a
                                 MUST!


      AORN Recommended Practice II
    “Eyes of patients and health care workers
     should be protected from laser beams.”

            Interpretive Statement I
     “Laser-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.”
     Laser eye penetration:

CO2
Erbium               Corneal absorption
Diode



Pulsed dye
Nd:YAG              Retinal absorption
Alexandrite
Different eyewear for different
        wavelengths!
               Laser signs:


  All doors to a laser
treatment room are to         VISIBLE LASER RADIATION
                              AVOID EYE OR SKIN EXPOSURE TO
                              DIRECT OR SCATTERED RADIATION




 be closed and have a         CLASS IV LASER PRODUCT




 laser specific danger
sign along with a pair
   of laser eyewear
prominently displayed.
  Fire hazard: be on the lookout for
flammable or combustible materials!

         Anesthetics
        Prep solutions
        Drying agents
          Ointments
           Plastics
           Resins
            Hair
                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
             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.
                    A laser should
                      always be in
                   “standby” mode
                  unless an operator
            SBY    is ready to use it.



“standby     “laser is
 please”   in standby”
 REMEMBER:


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

				
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posted:4/23/2012
language:English
pages:46