Low-Power Lasers

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Low-Power Lasers

• Jennifer L. Doherty-Restrepo, MS, ATC, LAT
• Entry-Level Master Athletic Training Education
  Program
• PET 4995 Therapeutic Modalities

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LASER

• Light
• Amplification of
• Stimulated
• Emission of
• Radiation

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Physics of the Laser

• Light energy transmitted through space as waves
  that contain tiny "energy packets" called photons
• Each photon contains a definite amount of energy
  depending on its wavelength (color)

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Physics of the Laser

• If a photon collides with an electron of an atom,
  it causes the atom to be in an excited state
• Atom stays in excited state only momentarily
• Atom quickly releases an identical photon to
  return to its ground state
• Process is called spontaneous emission

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Stimulated Emissions

• A photon released from an excited atom will
  stimulate another atom to return to its ground
  state
• For this to occur, an environment must exist with
  unlimited excited atoms
• This is termed population inversion

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Stimulated Emissions

• Population inversion occurs when there are more
  atoms in an excited state than in a ground state
• May be stimulated by an external power source
• Photons may be contained in a chamber

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Stimulated Emissions

• Mirrors are placed at either end of the chamber
• Photons are reflected within chamber, which
  amplifies the light and stimulates the emission
  of other photons from excited atoms

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Stimulated Emissions

• Eventually so many photons are stimulated that
  the chamber cannot contain the energy
• Photons of a particular wavelength are ejected
  through the semipermeable mirror producing
  amplified light through stimulated emissions

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Types of Lasers

• Classified according to the nature of material
  between two reflecting surfaces
• Crystal lasers
• Synthetic ruby (aluminum oxide and chromium)
• Neodymium, Yttrium, Aluminum, Garnet
• Gas lasers (under investigation in the U.S.)
• Helium neon (HeNe)
• Argon
• Carbon dioxide (CO2)

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Types of Lasers

• Classified according to the nature of material
  between two reflecting surfaces
• Semiconductor or Diode lasers (under
  investigation in the U.S.)
• Gallium-arsenide (GaAs)
• Liquid lasers
• Organic dyes lasing medium
• Chemical lasers
• Used for military purposes

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Laser Classification

• Laser equipment is grouped into four FDA classes
  with simplified and well-differentiated safety
  procedures for each
• Low power lasers used in treating sports injuries
  are categorized as Class I and II laser devices

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Laser Classification

• High power lasers "hot" lasers
• Thermal effects
• Surgical cutting and coagulation,
  ophthalmological, dermatological, oncological,
  and vascular specialties
• Low power lasers cold lasers
• Cause photo-chemical rather than thermal effects

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Laser Generators

• Power Supply
• Lasing Medium
• Gas, solid or liquid
• Pumping Device
• Creates population inversion
• Optical Resonant Cavity
• Chamber where population inversion occurs
• Contains reflecting surfaces

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Helium-Neon Lasers

• Gas lasers
• Deliver a red beam
• Wavelength 632.8nm
• Laser delivered in a continuous wave
• Direct penetration of 2 to 5 mm
• Indirect penetration of 10 to 15 mm

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Gallium-Arsenide Lasers

• Semiconductor lasers
• Invisible beam
• Wavelength 904nm
• Direct penetration of 1 to 2 cm
• Indirect penetration to 5 cm

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Techniques of Application

• Laser energy emitted from hand held remote
  applicator
• Tip should be in light contact with the skin
• Applicator should be directed perpendicularly to
  the skin

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Dosage

• Dosage reported in Joules per square centimeter
  (J/cm2)
• One Joule is equal to one watt per second
• Dosage is dependent on
• Output of the laser in mWatts
• Time of exposure in seconds
• Beam surface area of laser in cm2

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Dosage

• Dosage should be accurately calculated to
  standardize treatments and to establish treatment
  guidelines for specific injuries.
• Intention is to deliver a specific number of
  J/cm2 or mJ/cm2

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Pulsed vs. Continuous Laser

• With pulsed laser treatment, times may be
  exceedingly long to deliver same energy density
  as compared to a continuous wave laser

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Depth of Penetration

• Depends on type of laser energy delivered
• Direct effect
• Response that occurs from absorption of laser
  energy
• Indirect effect
• Lessened response that occurs deeper in the
  tissues

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Depth of Penetration

• HeNe lasers
• Direct effect 2-5 mm
• Indirect effect 8-10 mm
• GaAs lasers (longer wavelength)
• Direct effect 1-2 cm
• Indirect effect 5 cm
• Better for treating deeper tissues

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Clinical Applications

• Wound healing
• Immunological responses
• Inflammation
• Scar tissue
• Pain
• Bone healing

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Indications for Laser

• Facilitate wound healing
• Pain reduction
• Increasing the tensile strength of a scar
• Decreasing scar tissue
• Decreasing inflammation
• Bone healing and fracture consolidation

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Contraindications for Laser

• Cancerous tumors
• Directly over eyes
• Pregnancy