PRESENTATION 4- Basics of Laser in Dermatolgy It includes - Laser spectrum Definition Laser Classification of Lasers Laser Theories Laser terminology Laser Hazards

1. BASICS OF LASER

2. INTRODUCTION
L ight
A mplification by
S timulated
E mission of
R adiation
LASER is an acronym, first used by Gordon Gould in 1959

3.  1960- First laser of clinical significance, introduced
by Maiman, contained a ruby rod and emitted light
with a wavelength of 694nm (tattoos).
 1961- Nd:YAG laser (tattoos & supf vascular
lesions)
 1962- Argon laser (vascular lesions)
 1964- Carbon Dioxide laser
 1983- Theory of selective photothermolysis -
understanding of laser-tissue interaction.

4. QUANTUM MECHANICS
 Light- is an electromagnetic wave.
It consists of oscillating electric and magnetic fields travelling
through space.
 Wavelength- is the distance between two peaks on the wave.
Different wavelengths are seen by the eye as different colors.
e. g. Blue light has a wavelength of about 400 nm.
Red light has a wavelength of about 700 nm .

5. WAVE NATURE OF LIGHT
Light is an electromagnetic wave.
Different wavelengths in the
visible spectrum are seen by the
eye as different colors.
l
Wavelength
Red: l = 700 nm
Blue: l = 400 nm

6. PHOTON
 The “particle” of light is called a photon.
 It is not a material particle but rather “quantum”.
 Also called as quantum of electromagnetic
radiation or light.
 A photon is more accurately described as a
packet of energy.
 The energy of a photon is inversely proportional to
the wavelength of the light.

7. Electromagnetic spectrum

8. Lasers operate in the
ultraviolet, visible, and
infrared regions of the
spectrum.
Lasers in each spectral region
present unique safety issues.

9.  Visible light has a wavelength range of 400 – 700 nm and can
be seen by the eye.
 The near infrared has a range of 700 – 1400 nm. It cannot be
seen because the retinal receptors do not work at these
wavelengths. However, the optical elements of the eye
transmit the near IR and focus these wavelengths on the
retina. This produces an invisible retinal hazard and the
potential for serious eye injury in the near IR. The most
stringent laser safety precautions are required in this
wavelength range.
 The far infrared is completely absorbed by water before any
of the light reaches the retina. This protects the retina from
damage. These wavelengths can damage other parts of the
eye, but the absorption is spread over a larger area resulting
in a larger allowed exposure.
 The ultraviolet has the potential for photochemical damage to
both eyes and skin.

10. LASER SPECTRUM
10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102
LASERS
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 10600
Ultraviolet Visible Near Infrared Far Infrared
Gamma Rays X-Rays Ultra- Visible Infrared Micro- Radar TV Radio
violet waves waves waves waves
Wavelength (m)
Wavelength (nm)
Nd:YAG
1064
GaAs
905
HeNe
633
Ar
488/515
CO2
10600
XeCl
308
KrF
248
2w
Nd:YAG
532
Retinal Hazard Region
ArF
193
Communication
Diode
1550
Ruby
694
Alexandrite
755

11. THE PHOTON THEORY

12. PHOTON THEORY & SPONTANEOUS EMISSION
 When energy is absorbed by an atom, some of the electrons in
that atom move into larger, higher energy orbits.
 When energy is released by the atom, the electrons move to
smaller orbits.
 The lowest energy state is called the ground state. This is when
all the electrons are as close to the nucleus as possible.
 Higher energy states are called excited states. Excited atomic
states are not stable. Excited atoms tend to release energy in
the form of photons and drop to lower energy states.
 Ordinary light is produced by spontaneous emission as excited
atoms drop to lower energy levels and release photons
spontaneously.
 The result is light that is a mixture of many different
wavelengths, emitted in all directions, and has random phase
relationships.

13. STIMULATED EMISSION
 Laser light is produced by stimulated emission
 When excited atoms are struck by photons in the laser beam, they are
stimulated to emit their photons before they are emitted randomly by
spontaneous emission.
 In this process, two photons of light are released, and energy
required is provided to laser by external power source.
 All photons produced by stimulated emission have the same
wavelength, travel in the same direction, and are in phase.
 Each time process is repeated, no.of photons in laser cavity
increases.

15. POPULATION INVERSION
• Each time the process of stimulated emission is
repeated, the number of photons in the laser cavity
increases.
• When majority of the electrons are no longer in
their resting orbits but in an excited state, they are
described as having undergone population
inversion.
The significance of this is that stimulated emission
becomes more probable and light amplification
more significant.

16. STIMULATED EMISSION; “POPULATION INVERSION”; MORE
ATOMS HAVE EXCITED ELECTRONS, THAN RESTING
ELECTRONS

17. CHARACTER
OF LASER
INTENSE
BRIGHTNE
SS
COLLIMA
-TION
COHERE
NCE
MONO
CHROMATI
CITY

18. INTENSE BRIGHTNESS &
MONOCHROMATICITY:
• Light from a given source is of single wavelength. This
enables laser to selectively target chromophores in skin.

19. Coherence
Light emitted by a laser is in temporal and spatial
correlation that is waves are in phase in time and space.

20. Collimation
• Light rays are nearly parallel.
• It is a direct consequence of coherence.
• This means that the waves are parallel & non-
divergent.
• Diameter of the beam changes only minimally over
distance, unless it is focused by a lens.

21. CLASSIFICATION OF LASERS
No Universally Acceptable Classification.
Can Be Classified Depending Upon
1. Medium Used (gas,liquid And Solid).
2. According To The Pulse Characteristics Of The Beam,
Which May Be Continuous, Pulsed Or Quality Switched (Q-
switched)
3.According To The Treating Condition (eg:hair Removal,
pigmented Skin Lesion And Haemangoma).

22. 1.CLASSIFICATION DEPENDING UPON MEDIA
a) Gas lasers
b) Solid state lasers
c) Liquid lasers
d) Metal –vapor lasers
e) Chemical lasers

23. GAS LASERS
• Helium-neon Laser
• Argon Laser
• Krypton Laser
• Xenon Ion Laser
• Nitrogen Laser
• Carbon Dioxide Laser
• Carbon Monoxide Laser
• Excimer Laser

24. SOLID STATE LASERS
• Ruby laser
• Nd:YAG laser
• Er:YAG laser
• Neodymium glass (Nd:Glass) laser
• Titanium sapphire (Ti:sapphire) laser
LIQUID STATE
• Pulse dye laser

25. CHEMICAL LASERS
•Hydrogen fluoride laser
•Deuterium fluoride laser
•COIL (Chemical oxygen-iodine laser)
•Agil (All gas-phase iodine laser)

26. METAL –VAPOR LASERS
• Helium-cadmium (HeCd) metal-vapor laser
• Helium-mercury (HeHg) metal-vapor laser
• Helium-selenium (HeSe) metal-vapor laser
• Helium-silver (HeAg) metal-vapor laser
• Copper vapor laser
• Gold vapor laser

27. 2.CLASSIFICATION BASED ON PULSE CHARACTERISTICS OF
BEAM
A. CONTINUOUS: wave light consists of an uninterrupted beam
of relatively low power, such as is emitted by the CO2 laser.
MODIFICATIONS
i. MECHANICAL SHUTTERING:
The continuous beam is shuttered to deliver individual pulses of
energy.
Disadvantage: This alone may not be beneficial as these “pulses”
do not have sufficient energy to be clinically useful.
ii. SUPERPULSING:
It was developed so that the laser emitted a rapid train of higher
peak power pulses of energy.
e.g argon pumped tunnel dye laser, cupper vopour laser.
Disadvantage :These so called quasi-continuous lasers release
pulses which are so close together that there is insufficient time
for cooling between pulses.

28. B. PULSED
With the development of high peak power lasers with true
individual pulses containing enough energy in each pulse,
clinically significant tissue effects were achieved.
Eg: pulsed dye laser, normal mode alexandrite, diode,
ultrapulse CO2 laser.
Pulse duration: millisecond and microsecond(high range).
C. QUALITY SWITCHING/ Q SWITCHING
It is a means of creating very short pulses( 5-100
nanoseconds) with an extremely high peak powers.
It is achieved through an ELECTRO-OPTICAL
SWITCHING which consists of 2 polarisers. Depending
upon their alignment , these will either transmit/ block
light.

29. Pulse characteristics

30. LASER SYSTEM

31. LASER SYSTEM
1) LASER MEDIUM
Lasers are usually named after the constituents of the medium
GAS -argon, CO2, and excimer laser.
LIQUID -pulsed dye laser
SOLID -alexandrite, diode, Er:YAG, Nd:YAG,ruby lasers.
It determines the wavelength of the light created by stimulated
emission of radiation.
2) PUMP- external source of energy to excite the atoms to proper
energy state.eg: flashlamps, DC.
3) OPTICAL/RESONATOR CAVITY – Laser medium is contained in
the optical/resonator cavity and has a pair of mirrors at the ends of
the active medium. These mirrors are aligned to reflect the laser
light back and forth through the active medium.

32. • The high reflectance mirror has a reflectivity of nearly
100%. And partially refletive mirror at output end.
• The output coupler has a lower reflectance and allows
some of the laser light to pass through to form the
output beam.
• Low power lasers usually require most of the laser
light to keep the stimulated emission process going
and only a few percent can be allowed to pass into the
output beam.
• In very high power pulsed lasers, the output coupler
may have a transmission of over 50%.

33. 4) DELIVERY SYSTEM
The emitted light enters a delivery system for
transmission to the operator handpiece.
TYPES:
a) Fiberoptic cables
b) Articulated arms
Fibreoptic cables have the advantage of being lighter and
easier to operate and to maintain. However, they may
break when bending or twisting the fiber beyond its
tolerance during operation, movement, or cleaning.
Fibres are not sufficiently robust to transmit light
emissions from systems such as CO2, Er:YAG or short
pulse Q-switch lasers, where articulated arms containing
mutiple mirrors are required.

34. 5) HANDPIECE
Each delivery system ends in a
handpiece.
In this light can be focused by a lens
or transmitted as a collimated beam.
Either type can be scanned over a
predetermined area of the skin in order
to limit the time to which the skin is
irradiated.

35. CHROMOPHORE
The target molecule which absorbs a photon is known as a
chromophore.
TYPES:
1) ENDOGENOUS CHROMOPHORES-
CHROMOPHORE ABSORPTION PEAK
1)Melanin UV and Visible light
2)Hemoglobin UVA, blue(400nm)
green(541nm),yellow(577nm)
3)Water mid and far Infra red regions.
4)Collagen Visible and Near Infrared

36. 2) EXOGENOUS CHROMOPHORE
THERE ARE ALSO A NUMBER OF EXOGENOUS
CHROMOPHORES OF WHICH THE MOST
IMPORTANT IS THE TATTOO INK.

37. ABSORPTION SPECTRA
• Predicted from their perceived colour.
PERCEIVED COLOUR MAX. ABS. ʎ (nm) MAX. ABS. COLOR
RED 505- 560 GREEN
ORANGE 500-525 GREEN
YELLOW 450-510 BLUE- GREEN
GREEN 630-730 RED
BLUE 620-730 RED
PURPLE 550-640 GREEN- YELLOW-
ORANGE- RED
BLACK ALL ALL

38. LASER LIGHT & SKIN INTERACTION

39. FATE OF INCIDENT LIGHT:TISSUE OPTICS
1. REFLECTION:
About 4-6% of light is reflected at the level of the stratum
corneum.
2. ABSORPTION:
Absorption of photons is described by the
BEER’S LAW: the intensity of a particular wavelength which
is transmitted through tissue depends on its initial intensity
as well as on depth of penetration and extinction length(the
distance over which 90% of the beam is absorbed).
GROTTHUS DRAPER LAW : Light must be ABSORBED by
chromophore for clinical effect
When a photon is absorbed by a target molecule or
chromophore, all of its energy is transferred to that molecule
destroying it while other chromophores are spared.
This is the basis for selective skin laser surgery.

40. 3. SCATTERING:
- It is largely due to collagen in the dermis.
- 2 TYPES of scatter-
a. Weak scatter also k/a Rayleigh Scatter in all
directions, by molecules smaller than incident light
wavelength.
b. Other type by objects larger than incident light,
forward in direction.
- Scattering decreases with longer wavelengths,
making these ideal vehicles for targeting deep dermal
structures such as hair follicles.
-The wavelength 600-1200nm is an OPTICAL WINDOW into the
skin because there is not only low scattering but also limited
absorption by endogenous chromophores at these wavelengths.

41. 4. TRANSMISSION:
- Residual light is transmitted to the subcutaneous tissue.
- Shorter wavelengths (300-400nm)are scattered more
&penetrate less than 0.1mm.
- Longer wavelengths(600-1200nm) penetrate deeper
because they are scattered less.

42. LASER TERMINOLOGY
 ENERGY (JOULES) - That is contained in light expressed in
joules or Amount of work done.
 POWER (WATTS) – Time rate at which energy is emitted by
laser. Measured in watts.
 IRRADIANCE ( POWER DENSITY)- Concentration of beam of
light and expressed as power applied per unit area.
FLUENCE (ENERGY DENSITY) – Actual amt of energy
applied per unit area of target. It depends on exposure time.
TO INCREASE FLUENCE:
 Increase power
 Increase time
 Decrease spot size

43.  PULSE WIDTH- It is amount of time laser energy
applied. It should be shorter than the thermal relaxation
time (TRT) of the target to minimize thermal damage to
tissue surrounding target.
 PULSE FREQUENCY- Repetition rate of pulse.
Measured in hertz.
 SPOT SIZE- Beam diameter. Determines depth of
penetration.
LARGER SPOT- greater depth of penetration by reducing
scattering.
SMALL SPOT- scattering of photons and beam diffuses

44. Radial Distance (mm)
Skin
Depth
(mm)
-10 -8 -6 -4 -2 0 2 4 6 8 10
0
2
4
6
8
10
3 mm
Dia.
1-3 mm
Target Depth
Radial Distance (mm)
Skin
Depth
(mm)
-10 -8 -6 -4 -2 0 2 4 6 8 10
0
2
4
6
8
10
10 mm
Dia.
1-3 mm
Target Depth
1-3 mm
Target Depth
Under the same wavelength and fluence, larger
spot sizes allow deeper penetration.
The Effect of Dermal Scatter on
Beam Propagation

45.  THERMAL RELAXATION TIME
o TRT is the time taken for the target to
dissipate about 63% of the incident
thermal energy.
o It is related to the size of the target
chromophore, being proportional to the
square of the target diameter.
o It varies from few nanoseconds to
several hundred milliseconds or more.

46.  THERMAL DAMAGE TIME (TDT):
 This is the time to achieve selective damage of
the target.
 In case of hair removal, it is the time for the
entire target including the primary
chromophore (eg: melanin) and the surrounding
target (eg: hair follicle), to cool by about 63%
and includes cooling of the primary
chromophore as well as the entire target.
TDT is longer than the TRT as it allows for heat
diffusion from the chromophore throughout the entire
target.

48. SELECTIVE PHOTOTHERMOLYSIS
It is postulated that light can be used to selectively damage
or destroy a target chromophore if-
1)Its wavelength is selected so that there is as big difference
as possible between the absorption co-efficient of the
target & the surrounding tissue.
2)The energy fluence is sufficiently high to damage the
target.
3)Pulse duration is less than or equal to the thermal
relaxation time(TRT).

49. Extended theory of selective photothermolysis
• This theory explains the light assisted hair
reduction better.
• ABSORBER CHROMOPHORE: it is the one in
which heat is generated
• DISTANT TARGET: it is the one to which heat is
transmitted &which is damaged as a result.
• In case of hair removal the absorber
chromophore is the melanin in the hair shaft
and the matrix cells and the distant target is the
stem cells of the isthmus.

50. TISSUE COOLING
 There are three primary objectives of surface cooling.
1) Preservation of epidermis. Unintentional heating of basal layer
leads to vesiculation, crusting and scarring.
The laser induced temp. rise of epidermis is proportional to
fluence and wavelength specific absorption by melanin.
2) To allow for delivery at higher fluences to intended target (hair
bulb). So higher fluences and high temp possible in target
structures.
3) Analgesia, as almost all cooling devices provide some pain
relief.
 Heat damage to the epidermis may result in
-blistering
-dyspigmentation or scarring
And is particularly likely in pigmented skin.

51. To reduce this risk:
1) The wavelength should be optimized with
respect to the absorption characteristics
and depth of the target chromophore.
2) The use of long pulses and cooling of the
epidermis
This enhances safety in pt.
Cooling can be done before pulse(pre)
During pulse (parallel) or after(post)
Post cooling may prevent retrograde
heating from damaging the skin.

52. TYPES OF COOLING
1)COLD AIR CONVECTION: Air chilled to temperatures as low as -
30 degrees C, is directed onto the area to be treated. The Zimmer
directs -10 degree C at rapid rate (1000L/m)
2)CONTACT COOLING: This may involve ice-packs or more
sophisticated systems which pass chilled water between
colorless and transparent plates which are usually sapphire.
3)CRYOGEN SRAY(DYNAMIC COOLING): A frozen gas is sprayed
onto the skin immediately before the laser pulse. It is the most
efficient way of precooling.

53. ADVANTAGES OF COOLING
 One important benefit of epidermal cooling has been to
allow treatments at higher fluencies than would otherwise
be considered safe, and thereby enhanced treatment
efficacy, which has made it possible to reduce the number
of treatments required.
 Cooling has also made it possible to safely treat patients
with all skin types.
 It also decrease the pain associated with treatment thus
reducing the need for topical or local anesthetic.
 Excessive cooling may cause cryogen injury.

54. TYPES OF LASER HAZARDS
1. Eye : Acute exposure of the eye to lasers of certain
wavelengths and power can cause corneal or retinal
burns (or both). Chronic exposure to excessive levels
may cause corneal or lenticular opacities (cataracts) or
retinal injury.
2. Skin : Acute exposure to high levels of optical radiation
may cause skin burns; while carcinogenesis may occur
for ultraviolet wavelengths (290-320 nm).
3. Chemical : Some lasers require hazardous or toxic
substances to operate (i.e., chemical dye, Excimer
lasers).
4. Electrical : Most lasers utilize high voltages that can be
lethal.
5. Fire : The solvents used in dye lasers are flammable. High
voltage pulse or flash lamps may cause ignition.

55. LASERS AND EYES
 Laser light in the visible to near infrared spectrum (i.e., 400
- 1400 nm) can cause damage to the retina resulting in
scotoma (blind spot in the fovea). This wave band is also
know as the "retinal hazard region".
 Laser light in the ultraviolet (290 - 400 nm) or far infrared
(1400 - 10,600 nm) spectrum can cause damage to the
cornea and/or to the lens.
 Visual disorientation due to retinal damage may not be
apparent to the operator until considerable thermal damage
has occurred.

56. CONTROL MEASURES
 Eye protection, eyeshields and goggles.
 Operating room doors and windows
should be covered.
 Reflectance surfaces should be draped.
 Smoke evacuators placed in room.
 Explosive chemicals stored away.

57. THANK YOU
Thank You