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 (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 Cosmic AM Radio
The word laser is an acronym…it stands for: Light Amplification by Stimulated Emission of Radiation
Nucleus: protons & neutrons Electrons in Orbit Atoms of any substance are made up of electrons, protons and neutrons.
Excited stage Resting 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 photon (similar to the one absorbed): this is called spontaneousemission. Spontaneous emission
Stimulated 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.
There are four basic components to every laser: •Lasing medium •Optical cavity •Power source •Delivery system
Optical cavity Laser beam Lasing medium Power source Totally reflective mirror Partially reflective mirror Laser diagram: 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 Ordinary Light Laser light is monochromatic: the wavelength approaches unity.
Laser light is coherent: the light waves are spatially and temporally in phase. Laser light Regular “white” light
Laser Laser light is collimated: the light waves are parallel and not divergent.
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.
There are four basic laser parameters: • Wavelength • Pulse duration • Spot size • Fluence
Reflection Scattering Transmission Absorption Absorption is necessary for effect on tissue.
ABSORPTION Oxyhemoglobin Melanin 400 500 600 700 800 Wavelength: chosen partly based on the absorption curve of the targeted chromophore. • Chromophores of interest in dermatology are: • Haemoglobin • Water • Melanin 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
Laser focusing lens Focal spot Focal length Distance gauges are used to set the required spot size at the tissue surface Focal Plane
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
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
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.
Eye protection is a MUST! AORN Recommended Practice II“Eyes of patients and health care workersshould 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: CO2Erbium Diode Corneal absorption Pulsed dye Nd:YAGAlexandrite Retinal absorption
VISIBLE LASER RADIATION AVOID EYE OR SKIN EXPOSURE TODIRECT OR SCATTERED RADIATION CLASS IV LASER PRODUCT 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.
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.
SBY “standby please” “laser is in standby” A laser should always be in “standby” mode unless an operator is ready to use it.
REMEMBER: • Laser sign • Doors closed • Windows covered • Eye protection • Standby mode • Fire • Plume • Electrical safety