basic knowledge in laser dermatology. editor

1. Hints
laser in dermatology

2. LASER
• Light
• Ampilification
• Stimulated
• Emission
• radiation

4.
Light:
is electromagnetic radiation that is visible to
the human eye, and is responsible for the sense
of sight.

9. Albert Einstein in 1905 in the Swiss patent
office in Berne (Lucien Chavan).
(Courtesy, The Albert Einstein Archives, The
Jewish National and University Library, The
Hebrew University of Jerusalem, Israel.)
1919
Stimulated emission

10. Maser (Theodore Schawlow&Charles Townes)

11. Theodore maiman 1960
Ruby

12. Leon goldman
Father of laser medicine and surgery

18. Types of Lasers
Gas Argon , CO2, Excimer laser
Dye Pulsed dye laser
Solid Ruby, Nd YAG and Er Yag
Semiconductor Diode laser
Laser light can be delivered in pulses, continuous wave, or
pseudo-continuous wave forms.

19. Laser components
Optical cavity or the resonating tube:
where the amplification of stimulated emission
occurs.
Laser medium:
This could be solid, liquid, or gas.
Energy source:
which pumps energy to the laser medium to
produce the population inversion.
Wave-guide:
as fiber-optic cable.

20. LASER tissue interactionLASER tissue interaction

21. When the skin is exposed to LASER, it could be
transmitted, or scattered by the skin structures, or
absorbed by the chromophores.
Chromophores as oxyhemoglobin, melanin, tattoo
ink or water.

22. Grothus-Draper photobiology law
Light should be absorbed to have a
tissue effect if there is no light
absorption there will be no effect.
Absorption is controlled by
wavelength of laser and the
chromophore.

23. 1.Photothermal
2.Photochemical
3.Photomechanical

25. Theory of selective photothermolysis
In 1983 Drs. R.A. Anderson and J. A. Parrish
proposed this theory where a chromophore can be
selectively damaged with a light pulse of an
appropriate wavelength and suitable pulse duration
shorter than the thermal relaxation time of that
chromophore.

26. • Thermal Relaxation Time (TRT)
– Time taken for target to dissipate 50% of the
energy absorbed to surrounding tissue
– Or time needed for cooling of a given light
absorbing site e’in skin
– TRT is roughly equal to the square of the diameter
of target structure
– TRT in sec.= ~ d² in mm
– Second(S)=
• 10³ millisecons(ms)
• 106 microsecond( µs)
• 109 nanosecond (ns)
• 1012 picosecond(ps)
• 1015 femtosecond
• 1018 attosecond

27. TRT
target size TRT
Melanosome
Dermal
capillary
0.5-1 µm
0.1 mm
0.25-1 µs
10 ms

28. 1. Exposure time = or < TRT of target lead to
selective heating of target without
damaging surrounding tissue
2. Exposure time > TRT of target lead to heat
diffusion to surrounding tissue
1.2.

29. Thermal relaxation time
It is time of an object to loose heat energy to the
surroundings through thermal diffusion (The time to
disperse the heat absorbed during a laser pulse.)

30. Pulse duration
It is the time the laser is in contact with the target
cell (Chromophore).

31. Laser parameters
Energy fluence (Energy density) Joules/cm2
= energy delivered to a given unit area for each
single pulse.
Irradiance (Power density) (Watt/cm2
)
= rate of energy delivery = intensity of the energy
delivered.

32. Efficacy of laser depends upon:
 The target chromophore
 Wavelength
 Pulse duration
 Energy density