Introduction to Lasers
and Light Therapy
KEY T ERMS
ablation
absorption
absorption coefficient
active medium
bipolar radiofrequency
energy
chromophore
delivery system
dispersing electrode
Electromagnetic
Spectrum of Radiation
fluence (radiant energy)
impedance
indication or application
infrared
Intense Pulsed Light (IPL)
irradiance
joules
laser
LED
maser
melanin
micron
modulate
monochromatic
monopolar
nanometer
optical resonator cavity
oxyhemoglobin
photochemical or
photodynamic therapy
photomodulation
E
L
A
S
photons
polychromatic
power density
pulse duration
pulse width
selective photothermolysis
spot size
TEM mode
thermal relaxation time
( TRT )
ultraviolet
watt
wavelength
R
O
F
T
O
N
CHAPTER
1
L E A R N IN G O B J EC T I V E S
After completing this chapter you should be able to:
1. Describe how laser light is created.
2. Differentiate between stimulated emission and spontaneous
emission of radiation.
3. Describe the four properties of laser light.
4. Review the four characteristics of laser light.
5. List the three major chromophores in the skin.
6. Describe an Intense Pulsed Light system.
7. Review the differences between bipolar and monopolar
radiofrequency energy.
1
2
CHAPTER 1
INTRODUCTION
P
Indications or
application
Any sign or circumstance indicating that
a particular treatment is appropriate or
warranted.
rocedures for rejuvenation of the face and body are actively
pursued by the public at a staggering rate. According to the
American Society for Plastic Surgery (ASPS) cosmetic procedures have risen to 11.8 million. That is a 446 percent increase between
1997 and 2005 and a 7 percent increase over 2006.1 As a practitioner performing these procedures, one needs to have a comprehensive understanding of the physics, tissue interactions, delivery systems, and
multitudes of devices commonly used in today’s cosmetic market. It will
be mandatory that you master your device’s operations along with specific parameters per indication or application to produce safe, effective,
and reproducible outcomes for your client.
R
O
F
T
O
N
Maser
Microwave Amplification by Stimulated
Emission of Radiation.
E
L
A
S
HISTORY OF LIGHT AND
EN ER GY DEVIC ES
As you may already know, the history of medical light sources began with
Albert Einstein in 1917, the same time most modern physics theories
originated. It was at this time that Einstein published his paper “Zur
Quanten Theorie der Strahlung” (“To the Quantum Theory of the
Radiation”) outlining the theory of laser light in the German journal
Physikalische Zeit.2 He was able to mathematically describe the emission
of spontaneous sunlight and theorize how a brilliant form of light
energy could be artificially created. However, it wasn’t until 1958 that
Theodore Townes and Arthur Schawlow published the first theoretical
calculations for a visible light source at Bell Laboratories. The maser
(microwave amplification by the stimulated emission of radiation) was
initially created as the first type of invisible light using ammonia gas and
microwave radiation. In May 1960, Theodore Maiman of the Hughes
Aircraft Research Laboratories created the first laser at the 694 nanometer (nm) red spectrum of light from a ruby crystal. This first pure form
of light revolutionized the medical field in the areas of dermatology and
ophthalmology.
Lasers quickly moved from the research domain into the physician’s hands. The neodymium-doped glass laser was created in 1961.
(See Figure 1–1.) In 1962, the argon laser, which used two visible wavelengths of blue-green light, was created for ophthalmologists to use in
the treatment of retinal disorders. The first neodymium-doped yttriumaluminum garnet ( Nd:YAG) laser was developed in 1964 for experimental removal of tattoos and vascular lesions. In 1965, the first carbon
INTRODUCTION TO LASERS AND LIGHT THERAPY
Figure 1–1 An early Nd:YAG laser system. Courtesy of
Technology Concepts International - Penny Smalley RN.
R
O
F
T
O
N
3
E
L
A
S
dioxide CO2 laser was created from CO2 gas. T. Polanyi developed an
articulating metal arm with aligned mirrors to direct the CO2 laser to distant anatomical areas.3 Subsequently, an ear, nose, and throat (ENT )
surgeon named Dr. Geza Jako used this device to treat vocal cord lesions
with the assistance of a microscope. From this time on, laser research and
development ignited the technological explosion of devices that we experience today. There are presently more than 150 different types of laser
light and energy devices sold in today’s cosmetic market.
PHYSICS
In learning about lasers, light sources, and radiofrequency devices, the
first requirement is to grasp the basic technical background and terminology needed to understand today’s cosmetic field. Numerous questions
may arise when first delving into this complicated arena. What causes a
laser light to be created? What bio-tissue effects occur? What is a wavelength of light? Why can’t you use one device to treat all your client’s
concerns? What are the advantages of these laser/light devices compared
to conventional equipment? What is the difference between a laser and an
Intense Pulsed Light (IPL) versus an LED device? The intent of this
chapter is to lay the foundation for understanding the science and art of
cosmetic laser and light source treatments.
4
CHAPTER 1
Electromagnetic Spectrum of Radiation
Ultraviolet
Radiation that we cannot see; part of the
electromagnetic spectrum.
Infrared
Invisible light.
Electromagnetic
Spectrum of Radiation
Made up of all of forms of energy whose
spectrum extends from long radio waves
to ultrashort gamma.
Photons
Miniscule units of electromagnetic
radiation or light.
To learn about how laser light is created, one needs to start with the basics
of physics. Laser light is in essence a high-powered flashlight that has
been efficiently harnessed to provide a narrow, directional beam of light.
The sun emits rays of light that are composed of a multitude of invisible
and visible forms of energy. This light can be broken down into invisible
ultraviolet energy, invisible infrared light, and visible light. As the sunlight passes through the atmosphere, ultraviolet light is absorbed primarily by the ozone layer in the upper atmosphere. The invisible infrared
energy is generally absorbed by water and carbon dioxide molecules in
the atmosphere, and the visible light penetrates down to the earth surface.
The Electromagnetic Spectrum of Radiation is made up of all of these
forms of energy whose spectrum extends from long radio waves to ultrashort gamma. (See Figure 1–2.) The emissions that make up this spectrum travel at the speed of light.
The type of energy in the electromagnetic spectrum of radiation is
composed of discrete particles called photons. Photons travel at the
speed of light in the form of a wave at 186,000 miles per second.4 Each
type of energy, whether it is visible or invisible, generates a particular
waveform. A wavelength refers to the physical distance between the top
(amplitude) of one wave to the top of the next wave. (See Figure 1–3.)
Each wavelength of light energy that is generated is measured in units
of length called nanometers and micrometers. A nanometer (nm) is
R
O
F
T
O
N
Wavelength
The distance between two consecutive
peaks or troughs in a wave.
Nanometer
One billionth of a meter, or 10-9.
E
L
A
S
Figure 1–2 The Electromagnetic Spectrum of Radiation. Courtesy of
Technology Concepts International - Penny Smalley RN.
INTRODUCTION TO LASERS AND LIGHT THERAPY
5
Amplitude
Wavelength
Short wavelength
High frequency
High intensity
Efficient for light skin
Long wavelength
Low frequency
Low intensity
Mild for dark skin
R
O
F
T
O
N
E
L
A
S
Figure 1–3 A wavelength is the measurement between the distance of
two peaks in a wave.
a billionth of a meter, or 10−9. A micrometer (or micron; [mm]) is a
millionth of a meter, or 10−6. One needs to be aware of the metric system
when working with lasers, for a laser’s light is designated by its wavelength, which can be referred to either in nanometer or micrometer measurement. For example, Nd:YAG’s wavelength is labeled either 1064 nm
or 1.06 mm.
The human eye responds primarily to energy wavelengths between
400 nm and 750 nm. The energy in this range is visible radiation, which
we can simply call “light.”5 The colors run from one to the next as seen
with the particular color properties of the rainbow’s spectrum of light. For
example: 488 nm is blue, 532 nm is green, 577 nm is yellow, 590 nm is
orange, and 694 nm is deep red. (See Figure 1–4.) However, the majority
of the lasers used in the esthetic field are invisible to the eye and fall in the
infrared spectrum of light. Cosmetic infrared lasers can be classified as
either near-infrared (700 nm to 1200 nm) or mid-infrared (1200 nm to
3000 nm) wavelengths of light. Even though they are invisible, they are
still safe and very therapeutic in the cosmetic industry.
Around 9 percent of the energy from the sun is in the form of ultraviolet wavelengths (180 nm to 400 nm).6 Ultraviolet radiation can have
enough energy per photon to cause molecules to become ionized and emit
particles.7 The ionization of these particles can be considered hazardous to
Micron
A millionth of a meter, or 10-6.
Did Y ou Know?
A wavelength’s characteristics
are specific to the type of laser
light source used. For example, a
diode laser used for hair removal
has a wavelength of 800 nm and
penetrates only 2–3 millimeters
(mm), whereas an Nd:YAG laser
has a wavelength of 1064 nm
and penetrates 3–5 mm deep.
CHAPTER 1
Holmium
CO2
10600 nm
2940 nm
2100 nm
Nd: Er:YAG
YAG
1064 nm
800 nm
694 nm
577−630 nm
Ruby
KTP
Dye
Excimer Argon
532 nm
x-rays
cosmic
rays
Diode
488−514 nm
Sample
Laser
Types
190−390 nm
6
microwaves
TV and
radio
waves
UV
400 nm
E
L
A
S
VISIBLE 700 nm
INFRARED
Figure 1–4 The visible and invisible portions of the electromagnetic
spectrum of radiation with the most common lasers identified.
human beings. Potential risks are associated with intense exposure to
ultraviolet light as seen in DNA cellular damage, mutations, and possible
cancer. These types of energy are not commonly used in the esthetic clinic
and most often are seen in the forms of X-ray and nuclear ultraviolet radiation. Many of your clients may ask if exposure to laser light will be harmful or have the potential to cause cancer. You can reassure your clients by
relating that, at the present time, there are no known anecdotal or published articles linking cancer diagnosis to cosmetic laser treatments. A
recently published study by H. Chan, MD, in which 50 treatments on
mice were performed over 6 months with different types of lasers and
Intense Pulsed Light systems, found no evidence of skin cancers or skin
toxicity.8 The types of laser and light sources to be used in your esthetic
practice fall into the safe areas of the Electromagnetic Spectrum of Radiation, with no known short-term or long-term exposure hazards.
R
O
F
T
O
N
Creation of Laser Light
The Bohr atomic model provides the basic theory of laser energy. A positively charged nucleus consists of protons and neutrons, with negatively
charged electrons circulating in an orbit. In their resting state, electrons
are at their lowest energy level.9 When an intense energy source is applied
to a molecule, the energy is absorbed for a fraction of a second and
orbiting electrons move to a higher, excited orbit. As the electrons
descend back down to the ground level, this energy is released as a photon
with a particular wavelength on the Electromagnetic Spectrum of Radiation. This reaction is called spontaneous emission of light and occurs naturally, as seen with sunlight. (See Figure 1–5A.)
INTRODUCTION TO LASERS AND LIGHT THERAPY
Photon
7
Electron
Photons
A. Spontaneous Emission
B. Stimulated Emission
Figure 1–5 Spontaneous emission showing excited electrons releasing
random wavelength photons as they fall back to their resting state.
Stimulated emission showing electrons releasing two identical photons,
one recently absorbed and the other from the excitation phase. Courtesy
of Lumenis® Ltd.
E
L
A
S
The word laser is really an acronym that stands for “light amplification by the stimulated emission of radiation”. Einstein proposed the theory of stimulated emission of light, which stated that, in an excited state,
a photon of energy would be produced, in the presence of other identical
photons. He also proposed that two identical photons would travel in the
same direction.10 Stimulated emission occurs when an already-excited
electron absorbs a newly created photon of equal energy. Upon descending back to its resting state, two identical photons are now released.
(See Figure 1–5B.) This formation of a laser beam occurs inside the tube
or head of your laser. Turning on your laser machine will produce intense
energy by either creating high-voltage electricity or stimulating a highintensity light source, like a krypton arch lamp. Electrons become stimulated by this intense energy and spontaneously create identical photons as
they collide with mirrors placed on opposite ends of the laser tube. These
mirrors reflect the emitted photons back and forth between the mirrors.
Two photons collide with two more photons, resulting in four photons,
and a chain reaction occurs. Each time they pass back through the medium, more photons are created, until a population inversion occurs. Population inversion is defined as state where more than 50 percent of the
photons emitted are identical to each other.11
In general, laser systems consist of six basic components: the active
medium, the laser tube or resonator, the power supply, the cooling system, the software and microprocessor, and the delivery system. Within
every laser device, there is a laser tube or optical resonator cavity. The
optical resonator can be constructed in numerous ways. Some consume
more than a third of the device’s size, and others are so small that they fit
inside the handpiece. Universally, the optical resonator is constructed
R
O
F
T
O
N
Laser
A device that emits radiant energy at
variant frequencies for therapeutic
purposes.
Optical resonator
cavity
The part of the laser that contains the
active medium.
8
CHAPTER 1
Pumping Cavity
Laser Light Target Tissue
Laser Medium
(e.g. crystal, gas, dye)
Reflective
Mirror
R-100%
Partially Reflective
Mirror
R-90%
E
L
A
S
Energy Source
(e.g. flashlamp, electric current, laser)
Figure 1–6 The optical resonator or laser tube inside a laser system.
Two mirrors are positioned on either side of the laser medium; one is
100 percent reflective and the other is about 90 percent reflective. When
the hand switch or foot pedal is depressed, light exits the laser head
and is directed to the tissue.
R
O
F
T
O
N
Active medium
The part of a laser that absorbs and
stores energy.
with mirrors positioned on opposite ends inside a sealed glass tube or a
metal reflective cavity. (See Figure 1–6.)
The optical resonator contains some type of active medium, gas,
liquid, or solid, that is stimulated to create the laser light. Common gas
medium lasers can contain common argon, carbon dioxide, or heliumneon gas particles. Liquid medium laser tubes have organic liquid or dye.
A crystal medium is usually a synthetic, manufactured crystal of yttriumaluminum garnet ( YAG) particles that are doped with certain elements
such as holmium, neodymium, and thulium, or erbium electrons. Different types of laser systems are named in reference to their activated
medium. Diode lasers are solid-state devices manufactured out of semiconductor crystals or diode arrays. Diode lasers emit light when an electrical current is passed through a very small semiconductor chip with
micro-mirrors positioned directly onto each end.12 These devices tend
to be smaller, lighter, more economical, and more durable due to the simplicity and stability of the components.
Most power supplies require a single-phase 110 or 220 Value Anti
Cheat ( VAC) outlet. It is important to check the electrical requirements
prior to installation of your laser or light source. The voltage that is generated inside a laser system is intense enough to cause electrocution if an
untrained individual attempts repairs. Most medical laser products have
water or air cooling systems that remove the generated heat from the unit.
INTRODUCTION TO LASERS AND LIGHT THERAPY
Microprocessors and software programs execute the internal operations
of the device, create the laser energy, store data, and monitor the system’s
status and performance. A laser’s delivery system is the physical hardware needed to transfer the energy from the head of the laser to the treatment site.13 Delivery systems vary from emission of light through hollow
metal articulating arms, silica glass fibers, handpieces, optical scanners,
and endoscopes.
9
Delivery system
The physical hardware needed to transfer
the energy from the head of the laser to
the treatment site.
Characteristic of Laser Light
E
L
A
S
Laser light possesses unique intrinsic characteristics that differentiate
it from normal white light. Normal light from a lightbulb generates a
polychromatic or multiple-wavelength array of light. When this light
is projected through a prism, one sees the multitude of visible wavelengths in the colors of a rainbow. (See Figure 1–7A.) If the intensity is
plotted per wavelength, one sees a bell curve with predominance in the
yellow to orange spectrum of visible light.14 This white light is diffuse
in nature and can quickly disperse in space within a very short distance.
Laser light is different, which makes it easily harnessed for esthetic treatments. If a visible laser light, such as a red 640 nm wavelength, is passed
through a prism, one would see exiting only a distinct red beam. (See
Figure 1–7B.) If the intensity versus the wavelength is plotted, very high
intensities at a single red color would be observed. This light is brilliant in
nature and can travel over long distances with little to no divergence.
What are the characteristics that dictate this response?
R
O
F
T
O
N
A. Polychromatic
Figure 1–7 Natural light versus laser light.
B. Monochromatic
Polychromatic
Consisting of light of multiple
wavelengths, appearing as different
colors.
10
CHAPTER 1
Coherent Energy
Normal light from a lightbulb can be viewed as a multitude of frequencies, all out of phase with each other, all traveling in different directions.
Laser light is considered coherent because the laser photons travel
through space both temporally and spatially. Each wavelength of light
is composed of photons that are traveling in both time and space as a
single unit of energy. (See Figure 1–8.) This degree of precision and the
ability to manipulate the light make lasers unique compared to other
forms of technology.
Monochromatic Energy
Monochromatic
Light of one wavelength, which therefore
appears as one color.
E
L
A
S
A flashlight contains all the visible colored wavelengths of light, and the
combination of frequencies emits white light. Laser light differs because
it is monochromatic. That is, it is composed of one wavelength and one
color, whether visible or invisible. (See Figure 1–7B.) The type of molecule that is stimulated determines which wavelength of laser light will
be emitted. Each specific wavelength of light affects the depth of penetration and tissue reaction, and it creates a unique clinical effect.
R
O
F
T
O
N
Collimated Energy
Collimation refers to the non-divergent properties of laser light. Photons
from a flashlight or light bulb are composed of multiple wavelengths of
visible light. The light quickly disperses over time and space. However,
laser photons are parallel to each other and the diameter of the beam has
only minimal divergence. This property allows the laser light to remain
in phase for extended distances. The collimated nature of laser energy
Laser Light Photons
(Coherent)
Natural Light
Photons
(Incoherent)
Figure 1–8 Coherent laser light versus incoherent natural light. Courtesy
of Technology Concepts International - Penny Smalley RN.
INTRODUCTION TO LASERS AND LIGHT THERAPY
R
O
F
T
O
N
A.
B.
C.
11
E
L
A
S
Figure 1–9 A lens can be used to adjust the intensity of the laser
beam so that it can be used as (A) a cutting device, ( B) a coagulating
device, or (C) a heating device.
is essential to harness the beam to produce a focused spot by using a lens.
This high-powered, focused beam is required for many surgical and
esthetic procedures. (See Figure 1–9.) Laser light is used diversely
throughout the aerospace, military, engineering, entertainment, and
medical fields due to this unique property.
High Optical Energy
The last characteristic of laser light is its ability to reach high peak energies
for cutting, coagulating, ablating, and/or vaporizing tissue. Optical energy is determined by the laser’s power, the spot size, and the pulse duration
or pulse width. Laser light energy refers to the ability to do the work. A
common unit of energy that is used with lasers in the esthetic field is
joules. Joules is the term that describes the amount of energy delivered
to tissue multiplied by the time it takes to deliver it. Fluence, or radiant
energy, refers to the energy of the pulsed laser beam—it is expressed
in joules per cm2 ( J/cm2).15 (See Figure 1–10.) Most esthetic lasers are
pulsed to minimize thermal damage while destroying the target medium.
One may also note the machine’s energy display output expressed in
millijoules (mJ), or 1/1000 of a joule. Therefore, .82 J or 820 mJ both refer
to the same power output delivered to the treatment site.
Joules
Units of energy or work.
Radiant energy or
Fluence
The energy level of a laser; measured in
joules.
12
CHAPTER 1
E
L
A
S
Figure 1–10 Laser machine showing fluence in J/cm2.
R
O
F
T
O
N
Watt
The unit of power produced by a current
of 1 ampere acting across a potential
difference of 1 volt.
Power density
The rate of energy that is being delivered
to tissue by a laser light source; a
common unit of measurement with
continuous lasers ( W/cm2).
Irradiance
Power density, measured in watts per
centimeter squared ( W/cm2).
Pulse duration
The duration of an individual pulse of
laser light; usually measured in
milliseconds. Also known as pulse width.
Pulse width
See pulse duration.
Power is the rate of doing the work, and a unit of power is referred
to as a watt. Power density is the rate of energy that is being delivered to tissue by a laser light source and is a common unit of measurement with continuous wave lasers. With continuous wave lasers, a laser
beam can be constantly fired on the tissue. Power density is a parameter
that describes how powerful the laser beam is at the surface of the skin.
Irradiance, or power density, is measured in watts per centimeter
squared ( W/cm2).16
Pulse duration (or pulse width), which is measured in nanoseconds, microseconds, or milliseconds, is the timing of light energy, or
how long the laser is actually emitted on the skin. The longer the laser
stays on the tissue, the deeper the penetration and the more thermal
effects are produced. Some lasers are emitted in a continuous wave mode
in which the energy is fired the entire time one’s foot is on a foot pedal.
Other laser systems can deliver energies of light in individual pulses. The
superpulse and ultrapulse CO2 laser was designed to emit high-powered
peaks of energy with cooling time in between to reduce thermal damage.
However, most esthetic lasers are pulsed in a millisecond or microsecond
train. Q-switched (nanosecond) pulse duration is used commonly to
produce incredibly high-peaked powers, producing a photoacoustic
shock-wave effect to tissues.17 At 35 megawatts, the intense power of the
Q-switched laser can cause a mechanical disruption or breakdown of the
targeted object.
INTRODUCTION TO LASERS AND LIGHT THERAPY
13
Articulated Arm
Mirrors
Focusing
Lens
Mirrors
Target
Site
R
O
F
T
O
N
Figure 1–11 Illustration of spot size.
E
L
A
S
Spot size is also necessary to reach high optical energy. It is a measurement of the diameter of the beam that is in contact with the tissue.
(See Figure 1–11.) In changing the laser’s focusing lens, the spot size will
decrease or increase in diameter. The larger the laser beam’s spot size, the
less fluence is affecting the tissue. By reducing the spot size by half, one
increases the power density or fluence by a factor of four. Spot size in the
aesthetic field is usually measured in millimeters.18
The quality of the beam’s spot size as it comes in contact with the tissue can also be measured. Beam quality represents the distribution of the
laser energy across the beam diameter. TEM mode is common terminology that indicates how focused the beam is. This measurement can
be represented in a bell-shaped curve. The fundamental TEM00 mode
represents the most powerful, smallest, and most focused beam that is
generated, which retains its shape whether it is in focus or out of focus.19
The CO2 laser produces a TEM00 Gaussian beam, which is a superior
cutting laser due to the high power densities produced by the mode. Most
esthetic lasers, however, possess a top hat beam profile that represents an
equal distribution of energy across the entire spot size. (See Figure 1–12.)
Therefore, every time you turn on a laser device, you will affect the entire
target with each pulse and not produce a hot spot or unequal energy
outputs.
Spot size
The width of a laser beam.
TEM mode
Common terminology that indicates the
quality of the beam or the beam profile.
14
CHAPTER 1
Gaussian beam profile
Middle of beam is the
point of highest energy
Ablative
Esthetic Devices
Top hat beam profile
Energy is evenly distributed
across the beam
E
L
A
S
Non-Ablative
Esthetic Devices
Figure 1–12 The TEM modes of a laser’s beam profile.
R
O
F
T
O
N
Laser Properties
Laser radiation or light must be converted into different forms of energy
to produce therapeutic clinical outcomes. The distinctive properties of
laser light can cause four different light–tissue effects.
Absorption
The uptake of one substance into another.
Chromophore
Chemical that presents with color when
properly prepared; elements that laser
light is attracted to: blood, pigment, hair
color.
Ablation
Removal of surface material from a body;
usually associated with the presence of a
wound.
D i d Yo u K n o w ?
The absorption spectrum of light
illustrates how hemoglobin,
melanin, and water are absorbed
at different wavelengths of light.
Absorption
Absorption is the physical process in which light energy is converted by
the targeted tissue into either heat, an acoustic response, a chemical reaction, or cellular stimulation.20 (See Figure 1–13A.) The absorption or
attraction of a particular wavelength of light toward a specific target
controls the theory behind laser tissue interactions. When a specific
wavelength of light penetrates tissue, the absorption process actually
removes a certain amount of energy per unit of tissue.21 The laser light
can be absorbed by the skin’s epidermal surface or by material in the
tissue called a chromophore. A chromophore is the target in the epidermis or dermis that absorbs the laser beam’s thermal energy, causing the
desired ablation or destruction of the material. Common chromophores
in the body are water, hemoglobin in blood, collagen, and melanin.
Particular wavelengths are absorbed by particular chromophores.
Hemoglobin tends to have multiple absorption peaks in the visible
green–yellow spectrum of light, whereas with melanin, absorption gradually decreases the longer the wavelengths are. (See Figure 1–14.) The
beauty of esthetic laser systems is that one can manipulate the wavelength, energy output, and treatment parameters so that a specific
chromophore can be selectively destroyed while other chromophores are
INTRODUCTION TO LASERS AND LIGHT THERAPY
Laser
Laser
Mirror
Skin
A. Absorption
B. Reflection
Laser
Laser
Skin
R
O
F
T
O
N
Skin
C. Transmission
D. Scattering
Figure 1–13 The four universal properties of laser light.
E
L
A
S
Er: YAG
Laser
10,000
Low to High Absorption
Melanin
1,000
100
Water
Hemoglobin
CO2
Laser
10
1.0
0.1
0.01
0.001
200 nm
Invisible
Ultraviolet
15
1000 nm
Visible
2940 nm
10,600 nm 20,000 nm
Invisible
Infrared
Wavelength measured in nanometers
Figure 1–14 The absorption curve of hemoglobin, melanin, and water
to each wavelength of light.
16
CHAPTER 1
Melanin
Pigment of the skin, hair, and eyes;
protects skin from ultraviolet damage.
Oxyhemoglobin
Oxygenated blood.
• Hair removal lasers are absorbed by dark pigment, or melanin.
• Vascular lasers seek out blood or oxyhemoglobin as their
chromophore.
• Lasers that produce new collagen and rejuvenation tend to be
water or collagen absorbers.
• Lasers used for clearance of pigmented lesions or lentigos target
melanin in the epidermis and dermis.
• Tattoo lasers target specific dyes or tattoo pigment.
Figure 1–15 Different cosmetic lasers are absorbed by different
chromophores.
E
L
A
S
not. This is why there are so many different lasers, each with a different
purpose. (See Figure 1–15.)
R
O
F
T
O
N
Reflection
About 4 to 6 percent of natural light is reflected at the level of the stratum
corneum in the epidermis.22 A laser beam can also reflect off the skin
or any shiny surface such as a mirror, jewelry, or instrumentation. (See
Figure 1–13B.) The flatter or smoother the surface, the more intense
the reflection would be. Once reflected, the thermal properties of the
laser light could possibly cause a surface skin burn, fire, or even eye damage.
Transmission
The amount of transmission depends on the wavelength of the light.
Shorter wavelengths (300 to 400 nm) have very superficial penetration
of less than 0.1 mm into the epidermis. Visible light lasers and some
wavelengths in the near-infrared zones (400 nm to 1300 nm) can easily
pass through the epidermis and dermis and can penetrate deeper due to
less scattering. (See Figure 1–13C.) Some laser light can also be transmitted through clear fluids and even glass.23
Scatter
Scattering of laser light refers to the physical processes of the skin that
cause a beam to be deflected into some or all new directions. (See Figure
1–13D.) Scattering reduces the laser light’s energy as the beam is transmitted forward, laterally, and even backward. Scattering is important
with cosmetic laser systems because it rapidly reduces the therapeutic
effects on the tissue. In the skin, scattering is mostly due to the large
collagen molecules in the dermis. Scattering decreases with longer wavelengths, making it ideal for targeting deep dermal vessels and hair
INTRODUCTION TO LASERS AND LIGHT THERAPY
17
follicles. However, with some laser energies such as the Nd:YAG laser,
tissue penetration can cause deep thermal destruction at greater depths
but also can backscatter toward the client’s and operator’s eyes.24 The
greater the degree of backscatter, the higher the risk of optical injury.
Selective Photothermolysis
Selective photothermolysis governs today’s esthetic laser and light
practice. The theory of selective photothermolysis was published by
R. Anderson, MD, and J. Parrish in 1983 to elegantly describe the selective absorption of a specific light by a targeted chromophore.25 This light
(photo), delivers thermal energy that is engineered to cause selective
destruction, or lysis, of the designated target. Selective photothermolysis
refers to the use of a selected wavelength of laser light coupled with the
accurate pulse duration and energy settings to limit the destruction within the chromophore of the treated area. In essence, what one is trying to
achieve is targeted destruction of a blood vessel, hair follicle, or age spot
with minimal heating or side effects to the surrounding healthy skin.
To achieve selective photothermolysis, one needs to be aware of the
thermal relaxation time ( TRT ) of the target. TRT is the amount of
time necessary for a chromophore to lose 50 percent of the heat by diffusion.26 By limiting the exposure of the laser light to a time shorter than
the thermal relaxation time ( TRT ), the energy is contained in the selected target and does not produce collateral damage to the surrounding
tissue. Thermal relaxation time varies based on the size and density of the
target. The larger the object, the longer the TRT. Subsequently, TRT of
chromophores will vary, with very small tattoo particles having a TRT of
2 to 3 nanoseconds versus larger leg veins with a TRT of 300 milliseconds.
Therefore, a large target requires a longer laser pulse duration. Larger targets slowly absorb the heat, become damaged, and then dissipate the
remaining heat into the surrounding epidermis and dermis. The opposite
is also true—small objects with short TRT need shorter pulse durations
to quickly destroy the chromophore while sparing the epidermis. This
theory is essential in producing the desired therapeutic response in your
target while protecting the epidermis and not causing undesirable side
effects of blistering, hyper- or hypopigmentation, or scarring.
R
O
F
T
O
N
Selective
photothermolysis
The selective targeting of an area using a
specific wavelength to absorb light into
that target area sufficient to damage the
tissue of the target while allowing the
surrounding area to remain relatively
untouched.
E
L
A
S
Thermal relaxation
time ( TRT )
The amount of time it takes a substance
(e.g., dermal tissue), after heating, to
return to its normal temperature.
Did Y ou Know?
Used in pulsed lasers, energy
fluence is measured in joules
per square centimeter, ( J/cm2).
The pulse duration should be
longer than the thermal
LASER TISSUE EFFECTS
A laser beam’s effect on tissue can produce a multitude of responses
depending on the particular wavelength being used and the tissue that
is being treated. The best way to understand the cosmetic laser field is
relaxation time of the epidermal
tissue but shorter than the
thermal relaxation time of the
targeted chromophore.
18
CHAPTER 1
Absorption coefficient
A logarithmic measurement describing
how a particular wavelength of light will
be absorbed and to what depth.
to understand which lasers are used for which types of procedures and
why. The biological interactions between tissue and laser energy determine treatment outcomes and results.
The absorption spectra of the major skin chromophores dominate the
laser–tissue interactions.27 The absorption of light is described in Beer’s
Law, which states how a particular chromophore or medium absorbs a
specific wavelength of light. The absorption coefficient is a logarithmic
measurement describing how a particular wavelength of light will be
absorbed and to what depth.28 The absorption coefficient depends on the
presence and amount of chromophores in the skin. As laser light is transmitted through tissues, it interacts with the chromophores in the skin.
The absorption coefficient is determined by how deep the laser energy
will penetrate before only 10 percent of the energy remains. Shorter wavelengths in the visible light spectrum have a shorter absorption coefficient.
For example, the KTP laser at 532 nm has a penetration depth of .9 mm
before the energy is extinct. However, longer wavelengths like the
Nd:YAG laser at 1064 nm have a longer coefficient due to little scatter,
and they can penetrate up to 4 mm deep.
R
O
F
T
O
N
E
L
A
S
Photothermal Tissue Reactions
why the 532 nm wavelength is
With cosmetic procedures, most therapeutic effects are seen as cellular
reactions to thermal laser energy. As the laser’s radiant energy comes in
contact with tissue, the light is absorbed by its target chromophore and
transformed to heat. As a cell’s internal temperature reaches between
50° C and 100° C, most related tissue undergoes irreversible damage and
the destruction of cellular proteins.29 In other words, when exposed to
high energies, the intracellular content begins to boil and the cellular membrane ruptures, resulting in vaporization. Intracellular contents, denatured
proteins, particles of blood cells, viral and bacterial particles, and gases are
emitted in the form of smoke or laser plume. (See Figure 1–16.) What
remains is an area of necrotic tissue surrounded by a reversible damaged
zone of tissue that will eventually repair itself. The CO2 and erbium lasers
are classic examples of this type of ablative skin reaction which is used in
surgical procedures and for facial laser resurfacing by dermatologists and
plastic surgeons.
more appropriate for superficial
Vascular Lesions Response
facial vessels, and the 1064 nm
Vascular lasers target blood vessels by using a pulse duration synchronized close to the TRT of oxyhemoglobin, the targeted chromophore in
blood. Using the theory of selective photothermolysis, pulse durations
and fluence are modified to treat the different sizes of blood vessels. Larger vessels require longer pulse durations versus smaller capillaries, as seen
D i d Yo u K n o w ?
The longer the wavelength, the
deeper the penetration. That is
light is used primarily for deep
leg veins and more vascular
abnormalities.
INTRODUCTION TO LASERS AND LIGHT THERAPY
Figure 1–16 Cell being vaporized with the CO2 laser and
contents being emitted into the air.
R
O
F
T
O
N
19
E
L
A
S
in rosacea, that require shorter pulse durations. During a laser treatment,
the laser energy coagulates the blood and the heat is transmitted to injure
the vessel wall. The desired clinical response is either darkening or coagulation of the vessel, vasospasm in which the vessel blanches and then can
disappear, or vasoconstriction in which the vessel wall collapses. Smudging or erythema of the vascular component of the treatment site is also a
desired end point. Clearance of the vascular lesion is seen slowly over the
next three to six weeks as blood clots and wall debris are eliminated by the
macrophages. If purpura or bruising is noted, then TRT has been
exceeded and has ruptured the vessel wall. One should readjust the pulse
width or decrease the fluence to cause a more uniform heating of the
blood and cell wall without rupture of the vessel.30 The most common
lasers used in the cosmetic field for treatment of vascular lesions range
from the 532 nm to 1064 nm wavelengths.
Pigmented Lesions Response
Photothermal non-ablative devices can also be used very successfully for
the treatment of pigmented lesions. When melanin is the chromophore,
the absorption is the highest from the ultraviolet wavelengths into the
infrared spectrum at 1200 nm.31 Shorter visible wavelengths are more
effective for more superficial epidermal lentigos, with longer wavelengths
penetrating deeper for treatment of dermal lesions, such as Nevus of Ota.
Once the laser beam comes in contact with the targeted lesion, melanin
absorbs the light, which is then transformed to heat. The laser energy
breaks the melanin up into small particles, and melanin-containing cells
Caution:
Whenever melanin containing
lesions are treated, the
aesthetician needs to be sure
that they are non-cancerous or
pre-cancerous lesions.
20
CHAPTER 1
(melanocytes/keratinocytes) are damaged. The desired immediate
response is noted to be either erythema due to an inflammatory response
or darkening of the lesion due to epidermal accumulation of the particles.
The thermal absorption results in the destruction of the lesion with lightening or denuding of the epidermis.32 Usually one will note a crusting or
darkening over the pigmented lesions, which fades within 7 to 14 days.
Clearance is achieved with melanin particles and cellular debris being
eliminated by the immune system. The laser device one chooses will be
determined by whether the pigment is dermal or epidermal in nature.
The ability to determine this characteristic in the treatment of pigmented
lesions will dictate your client’s success or failure.
Collagen Stimulation Response
E
L
A
S
In the late 1980s and 1990s, ablative lasers such as the CO2 and erbium
lasers were created to improve mild to moderate rhytids, acne scarring,
and sun-damaged skin. The primary focus was to artificially produce collagen stimulation and remodeling. Because the targeted chromophore is
water, these lasers were engineered to remove microns of tissue with minimal adjacent thermal injury. During the vaporization of the epidermis
and a portion of the dermis, thermal damage occurred to the underlying
tissue, which produced collagen contraction and skin tightening. During
the days and weeks that followed, re-epitheliazation originated from the
hair follicles and other tissue to improve skin tone, skin texture, acne scarring, and facial wrinkles.33 The benefits, however, did not come without
prolonged recovery periods and reported side effects of hypopigmentation,
hyperpigmentation, scarring, and infection.
The current trend in esthetic procedures is to develop new technologies that are non-ablative in nature but produce the benefit of ablative
technologies. Non-ablative collagen remodeling has been associated with
infrared lasers that are selectively absorbed by water but penetrate deeply
into the dermis (1320 nm, 1450 nm, 1540 nm). With these different
wavelengths, the intent is for dermal injury while preserving the epidermis. Thermal injury to the dermis can result in fibroblast stimulation and
the production of new collagen. Non-ablative technologies are aimed at
treating mild to moderate photoaged skin with results more conservative
in nature than the ablative technologies. Recently, there has been an
explosion of new devices in the field of fractional resurfacing. Fractional
technology involves the delivery of pixel-size columns of thermal energy
that can penetrate into the dermis. (See Figure 1–17.) Multiple treatment
sessions are usually required and result in erythema and edema that can
last for several days to a week. Since the arrival of this technology, there
are now 18 different fractional technologies with a variety of wavelengths,
including the 10,600 nm CO2 laser.
R
O
F
T
O
N
INTRODUCTION TO LASERS AND LIGHT THERAPY
21
Microthermal
Zones of
Heat
Figure 1–17 Fractional laser technology creating
microthermal zones (MTZ) of heat into the tissue.
R
O
F
T
O
N
Photomechanical Tissue Response
E
L
A
S
Pulsed lasers can be mechanically engineered to create shock waves or
high-amplitude pressure waves in tissue.34 These pressure waves can
result in mechanical stress or photoacoustic reactions sufficient to break
apart calculi or stones in the bladder or ureter. Lasers like the Q-switched
laser shown in Figure 1–18 can also be pulsed a billionth of a second pulse
Caution:
Even though the same
wavelengths may be used to
produce a photothermal response
to tissue, these tattoo removal
devices are completely different
laser systems. The Q-switched
devices are specifically designed,
researched, and regulated for
tattoo removal only. One cannot
use a thermal laser or IPL device
on a tattoo! Doing so can cause
scarring and hypopigmentation,
along with subsequent litigation.
Figure 1–18 Q-switched YAG laser commonly used for tattoo removal.
Courtesy of Medlite Hoya Con Bio.
22
CHAPTER 1
width or duration to break up pigment and tattoo ink. With this extremely short pulse, the energy can be delivered at very high power densities (megawatts) to the targeted tissue. An acoustic shock wave is
delivered at the beam’s focal point and then travels away at the speed of
sound. The pressure wave then expands in all directions and causes a
mechanical breakdown of the melanin or tattoo dye. These Q-switched
devices can raise the tissue temperature to 1000°C in a billionth of a second, fast enough to explode particles of tattoo ink or pigment granules.
Clinically, one sees a whitening of the impact site due to a laser-stimulated
plasma reaction or localized gas formation in the epidermis and dermis.35 It can take three to six weeks for healing and clearance of the
fragmented particles by the body’s immune system white blood cells
(macrophages).
E
L
A
S
Photochemical/Photodynamic
Tissue Response
R
O
F
T
O
N
Photochemical or
photodynamic therapy
A chemical reaction activated by light;
this reaction selectively destroys tissue.
Photochemical or photodynamic therapy (PDT ) utilizes a particular
wavelength(s) of light that is reactive to a light-absorbing or photosensitive chemical compound. The reaction causes a biochemical response that
results in cell death or damage due to the conversion from oxygen (O2) to
a singlet oxygen (O). PDT research in the 1990s was conducted as a cancer therapy technique to kill invasive or penetrating tumors. The most
common cosmetic use of this technology today is the topical application
of ALA (Aminolevulenic Acid) to the skin of a client who is experiencing
precancerous or photodamaged skin changes. After a period of topical
application and incubation, the client is then fluoresced with a particular
laser wavelength, diffuse light source, or IPL. (See Figure 1–19.) Results
have been demonstrated to be as effective as other conventional techniques. PDT has gained acceptance and popularity as a more precise method
of targeting abnormal skin cells.36
Photoablative Tissue Response
Photoablative laser reaction is the process in which chemical bonds are
broken when tissue comes in contact with certain laser wavelengths.
What is experienced is a clean ablation with virtually no thermal effects
to the targeted tissue. Excimer lasers in the ultraviolet wavelength of
light, from 180 nm to 250 nm, can be used for this purpose as seen in the
LASIX procedure where the cornea is reshaped to correct refractive
disorders.
INTRODUCTION TO LASERS AND LIGHT THERAPY
Figure 1–19 Photodynamic therapy. ALA application on
an individual under LED lights for acne therapy.
Courtesy of DUSA Pharmaceuticals, Inc.
R
O
F
T
O
N
INTENSE PULSED LIGHT
23
E
L
A
S
In the mid-1990s, the first polychromatic, high-intensity flashlamp was
FDA approved for cosmetic use. This filtered flashlamp was marketed
as Intense Pulsed Light (IPL). Since its initial rocky development, IPL
devices have emerged as the gold standard of treatment of photodamaged
skin.37 Due to technological advances, IPL’s clinical outcomes are
becoming increasingly equivalent to established cosmetic laser systems.
They are presently even being coupled with lasers, light sources, and
radiofrequency devices.
Due to the variety of skin chromophores, it makes sense to use a
broadband light to treat the variety of skin abnormalities seen with photodamaged skin. IPL can act like a laser from the perspective of photothermolysis. Lasers usually treat one chromophore with one monochromatic
light, while IPL can target multiple chromophores with a spectrum of
visible and infrared light. Because IPL devices are now so versatile, they
can be used for treating a variety of vascular disorders, pigmented lesions,
hair removal, and photodamaged skin.
Intense Pulsed Light
(IPL)
Machine that uses a variety of filters to
diminish areas of color, both red and
brown, on skin (also called FotoFacial®
or PhotoFacial®).
Caution:
Remember IPL devices are Class
2 medical devices and numerous
injuries have been reported.
Education, hands-on training,
and demonstration of
competency is mandatory before
treating actual patients.
RADIOFREQUENCY DEVICES
Radiofrequency (RF) energy is a form of energy that differs from light or
optical energy. It is based on alternating energy waveforms that produce
localized, non-specific heat into the epidermis and dermis. RF energy
24
CHAPTER 1
wavelengths can range from one millimeter to hundreds of meters from
one waveform crest to the next.
Types of Monopolar RF devices
Impedance
Resistance to the flow of electrons.
Monopolar
These systems use rapidly alternating
electrical energy that creates resistance at
the epidermis and then converts to heat.
Dispersing electrode
A grounding pad, usually placed on the
client’s thigh or back at a point distant
from the treatment area.
Radiofrequency devices have commonly been used in the surgical arena for
the last 50 years for cauterizing bleeding vessels and reducing blood loss
during surgery. Radiofrequency energy production follows the principle
of Ohm’s Law, which states that the impedance (resistance) to the movement of the electrons creates heat relative to the amount of energy (current)
over time (seconds).38 Most traditional radiofrequency devices and some
present-day cosmetic units are monopolar systems. (See Figure 1–20.)
Monopolar systems use rapidly alternating electrical energy that creates
resistance at the epidermis and then converts to heat. Unlike lasers, which
operate on the theory of selective photothermolysis, radiofrequency
devices derive their clinical effects from the heat generated due to the tissue’s natural resistance.39 Once it heats the area, the current travels the path
of least resistance and seeks out an exiting pathway from the body. A
dispersing electrode (a grounding pad), is placed usually on the client’s
R
O
F
T
O
N
E
L
A
S
Figure 1–20 The effect of a monopolar versus a bipolar RF (radiofrequency) device. Courtesy of
Lumenis® Ltd.
INTRODUCTION TO LASERS AND LIGHT THERAPY
thigh or back at a point distant from the treatment area. The electrical current then exits the body via the grounding pad and returns to the machine.
The other type of radiofrequency device shown in Figure 1–20 does
not require a dispersing electrode. If the positive and negative electrodes
are placed at opposite ends of a handpiece, forceps, or treatment head,
then the current flows superficially in the path of least resistance from
one electrode to another. This is referred to as bipolar radiofrequency
energy, because the current is contained within the treatment head and
does not require a dispersing electrode. Bipolar radiofrequency technology is also being combined with lasers and light source for deeper penetration into the tissue and, in theory, a more effective outcome.
LIGHT EMITTING DIODES
( L E D DE V I C ES )
Bipolar radiofrequency
energy
If the positive and negative electrodes are
placed at opposite ends of a handpiece,
forceps, or treatment head, then the
current flows superficially in the path of
least resistance from one electrode to
another.
E
L
A
S
In contrast to thermal laser, there is an exciting new technology of nonthermal, non-ablative cellular stimulation called photomodulation.
Unlike other laser/light-based procedures that rely on heat and thermal
injury to improve the skin’s appearance, LED trigger a photobiochemical response. The process involves using low-level light energy to
modulate or activate cellular metabolism. LED devices are designed
to include panels of tiny diodes that are pulsed at an exclusive array
sequence. LED photomodulation can suppress collagenase, a collagendegrading enzyme that can accelerate our skin’s aging process.40 LED
can also stimulate the energy-producing mitochondria to enhance wound
healing and decrease the inflammatory response. LED devices are
becoming more accepted as an adjunct treatment for improving the signs
of aging and bolstering collagen production.
R
O
F
T
O
N
25
CONCLUSION
Understanding the basic physics behind laser, light, and radiofrequency
devices is the essential foundation toward gaining competency with any
aesthetic system. As an astute aesthetician, one needs to understand the
fundamental concepts of energy absorption along with the corresponding
bio-tissue effects. This knowledge will guide you in every step of the
decision-making process: selection of the appropriate client, selection of
the appropriate device, selection of appropriate parameters, and selection
of the appropriate safety control measures. Hopefully this chapter has
enabled you to appreciate the intensive research and development that
has painstakingly occurred throughout the years to develop today’s laser
and light devices.
Photomodulation
Non-thermal, non-ablative cellular
stimulation.
LED (Light Emitting
Diode)
A semiconductor diode that emits light
when an electrical current is applied to
the device.
Modulate
Activate cellular metabolism.
26
CHAPTER 1
> > > T O P 1 0 TIPS TO TAKE TO T H E C LINIC
1. Laser is an acronym that means “light amplification by the
stimulated emission of radiation.”
2. The Electromagnetic Spectrum of Radiation is made up of all forms
of energy whose wavelengths extend from invisible infrared, to
visible light, to invisible ultrashort gamma waves.
3. Laser light is different from other forms of light due to its
characteristics of coherency, collimation, and monochromaticity.
4. Fluence, or radiant energy, refers to the energy of the pulsed laser
and is expressed in joules/cm2 ( J/cm2).
E
L
A
S
5. Laser light absorption is the physical process in which light energy is
attracted to a chromophore and converted into heat.
6. Selective photothermolysis refers to light that delivers energy
that is engineered to cause selective destruction of the designated
target.
R
O
F
T
O
N
7. Q-switched lasers can cause shock waves that cause photoacoustic
effects sufficient to break apart dye tattoo particles.
8. Most cosmetic laser systems produce a photothermal effect to
tissue.
9. IPL devices emit a broadband, diffuse light source that is composed
of visible and infrared wavelengths of light.
10. Radiofrequency devices use alternating energy waveforms
that produce localized, non-specific heat in the epidermis and
dermis.
CHAPTER REVIEW QUESTIONS
1. List the three properties of lasers that are not shared by Intense
Pulsed Light.
2. What is the Electromagnetic Spectrum of Radiation?
3. Describe four laser–tissue interactions.
4. Discuss the concept of stimulated emission of radiation.
5. Describe the concept of selective photothermolysis.
6. Define the term irradiance.
7. What is a LED device?
8. Define the two types of radiofrequency devices.
INTRODUCTION TO LASERS AND LIGHT THERAPY
27
CHAPTER REFERENCES
1. Aesthetic Dermatology News. (2008, May/June), 30.
2. Resinisch, L. (1996). Laser physics and tissue interactions.
Otolaryngologic Clinics of North America, 29(6), 893–913.
3. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Vascular, pigmentation, scars, medical applications, 1.
Philadelphia: Mosby Elsevier Health Science.
4. JGM Associates, Inc. (1993). Therapeutic Applications of Advanced
Laser Products, 1, Tutorials. Burlingham, MA: Author.
E
L
A
S
5. Rockwell, J. & Chamberlain, J. (2000). RLI: Medical users guide for
laser safety. Cincinnati, OH: Rockwell Laser Industries.
6. Ibid.
7. Dennis, V., Crowgey, S., & Grimes, B. (1996). Laser series.
Unpublished manuscript.
R
O
F
T
O
N
8. Chan, H., Yang, C., Leung, J., Wie, W., & Lai, K. (2007). What is
safe: An introduction. ASLMS, 39, 8–13.
9. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Vascular, pigmentation, scars, medical applications, 1.
Philadelphia: Mosby Elsevier Health Science.
10. Resinisch, L. (1996). Laser physics and tissue interactions.
Otolaryngologic Clinics of North America, 29(6), 893–913.
11. Trost, D., Zacherl, A., & Smith, M. F. W. (1992). Surgical laser
properties and their tissue interaction. In F.W. Mansfield &
J. T. McElveen (Eds.), Neurological Surgery of the Ear, (pp.
131–161). Philadelphia: Mosby.
12. JGM Associates, Inc. (1993). Therapeutic Applications of Advanced
Laser Products, 1, Tutorials. Burlingham, MA: Author.
13. Trost, D., Zacherl, A., & Smith, M. F. W. (1992). Surgical laser
properties and their tissue interaction. In F.W. Mansfield & J. T.
McElveen (Eds.), Neurological Surgery of the Ear, (pp. 131–161).
Philadelphia: Mosby.
14. Resinisch, L. (1996). Laser physics and tissue interactions.
Otolaryngologic Clinics of North America, 29(6), 893–913.
15. ANSI Z136.3. (2005). American National Standard Institute for
Safe Use of Lasers in Health Care Facilities. Orland FL: Laser
Institute of America.
16. Smalley, P. J. Technology Concepts International.
28
CHAPTER 1
17. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Vascular, pigmentation, scars, medical applications, 1.
Philadelphia: Mosby Elsevier Health Science.
18. Dennis, V., Crowgey, S., & Grimes, B. (1996). Laser series.
Unpublished manuscript.
19. Trost, D., Zacherl, A., & Smith, M. F. W. (1992). Surgical laser
properties and their tissue interaction. In F. W. Mansfield & J. T.
McElveen (Eds.), Neurological Surgery of the Ear, (pp. 131–161).
Philadelphia: Mosby.
20. Trost, D., Zacherl, A., & Smith, M. F. W. (1992). Surgical laser
properties and their tissue interaction. In F.W. Mansfield & J. T.
McElveen (Eds.), Neurological Surgery of the Ear, (pp. 131–161).
Philadelphia: Mosby.
E
L
A
S
21. Goldman, M. (2006). Cutaneous and cosmetic laser surgery,
Philadelphia: Mosby Elsevier Health Science.
R
O
F
T
O
N
22. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Vascular, pigmentation, scars, medical applications, 1.
Philadelphia: Mosby Elsevier Health Science.
23. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Vascular, pigmentation, scars, medical applications, 1.
Philadelphia: Mosby Elsevier Health Science.
24. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Vascular, pigmentation, scars, medical applications, 1.
Philadelphia: Mosby Elsevier Health Science.
25. Goldman, M. (2006). Cutaneous and cosmetic laser surgery,
Philadelphia: Mosby Elsevier Health Science.
26. Trost, D., Zacherl, A., & Smith, M. F. W. (1992). Surgical laser
properties and their tissue interaction. In F.W. Mansfield & J. T.
McElveen (Eds.), Neurological Surgery of the Ear, (pp. 131–161).
Philadelphia: Mosby.
27. Goldman, M. (2006). Cutaneous and cosmetic laser surgery,
Philadelphia: Mosby Elsevier Health Science.
28. Goldman, M. (2006). Cutaneous and cosmetic laser surgery,
Philadelphia: Mosby Elsevier Health Science.
29. Dover, J., Lim, H., Rigel, D., & Weiss, R. (2004). Photoaging,
New York: Marcel Decker, Inc.
30. Dover, J., Lim, H., Rigel, D., & Weiss, R. (2004). Photoaging,
New York: Marcel Decker, Inc.
INTRODUCTION TO LASERS AND LIGHT THERAPY
29
31. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Vascular, pigmentation, scars, medical applications, 1.
Philadelphia: Mosby Elsevier Health Science.
32. Goldman, M. (2006). Cutaneous and cosmetic laser surgery,
Philadelphia: Mosby Elsevier Health Science.
33. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Vascular, pigmentation, scars, medical applications, 1.
Philadelphia: Mosby Elsevier Health Science.
34. JGM Associates, Inc. (1993). Therapeutic Applications of Advanced
Laser Products, 1. Burlingham, MA: Author.
35. Goldman, M. (2006). Cutaneous and cosmetic laser surgery,
Philadelphia: Mosby Elsevier Health Science.
36. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Vascular, pigmentation, scars, medical applications, 1.
Philadelphia: Mosby Elsevier Health Science.
R
O
F
T
O
N
37. Dover, J., Lim, H., Rigel, D., Weiss, R. (2004). Photoaging,
New York: Marcel Decker, Inc.
38. Goldberg, D., Rohrer, T., Dover, J., & Alam, M. (2005). Lasers
and lights: Rejuvenation, resurfacing, hair removal, treatment of
ethnic skin, 2. Philadelphia: Mosby Elsevier Health Science.
39. Dover, J., Lim, H., Rigel, D., Weiss, R. (2004). Photoaging,
New York: Marcel Decker, Inc.
40. Kronemyer, B. (2005, Jan/Feb). Gentlewaves obtain first FDA
approval for LED wrinkle treatment. Aesthetics Buyers Guide,
228–229.
E
L
A
S
R
O
F
T
O
N
E
L
A
S