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

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

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) 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)

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 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

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 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

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 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

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 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

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 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

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 (CO 2 ) 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 (CO 2 )

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 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

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 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

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 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

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

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 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

Gallium-Arsenide Lasers Semiconductor lasers Invisible beam –Wavelength = 904nm Direct penetration of 1 to 2 cm Indirect penetration to 5 cm Semiconductor lasers Invisible beam –Wavelength = 904nm Direct penetration of 1 to 2 cm Indirect penetration to 5 cm

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 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

Dosage Dosage reported in Joules per square centimeter (J/cm 2 ) 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 cm 2 Dosage reported in Joules per square centimeter (J/cm 2 ) 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 cm 2

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/cm 2 or mJ/cm 2 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/cm 2 or mJ/cm 2

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

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 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

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 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

Clinical Applications Wound healing Immunological responses Inflammation Scar tissue Pain Bone healing Wound healing Immunological responses Inflammation Scar tissue Pain Bone healing

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

Contraindications for Laser Cancerous tumors Directly over eyes Pregnancy Cancerous tumors Directly over eyes Pregnancy