Advance dentistry

1. Laser physics

2. 1. What is a laser?
2. How does it work?
3. What are some of the properties that we
care about?
4. The laser types.

3. Light is composed of very large numbers of small
quanta of energy named “photon” behave as a sine
wave propagate in vacuum in a speed of light.
Wavelength is the distance over which the wave
repeats itself and is represented by the Greek letter
λ (lambda). Each color of visible light has its own
characteristic wavelength.

4.  If the light has single wavelength (only one λ) then it is called
(monochromatic light).
 All common light sources emit light of many different wavelengths
(polychromatic).
 White light contains all, or most, of the colors of the visible spectrum.
 Ordinary colored light consists of a broad range of wavelengths covering
a particular portion of the visible-light spectrum

5. 5
White light consists of a mixture of many different wavelengths. A prism can be
used to disperse white light into its component wavelengths (colors).
Dispersion of white light by a prism

6. Laser is light amplification by stimulated
emission of radiation (laser )
Properties of Laser Beams
The most characteristic properties of laser
beams are :
(i) Monochromaticity
(ii) Coherence
(iii)Directionality
(iv) Brightness ( Intensity )

7. 7
Unique Properties Of Lasers:
Laser light has unique properties compared with other
light sources. These properties are:
1 – Monochromaticity
 The color of the light is determined by the length of its
wave (λ).
 Laser light is single colored light (has one λ, or
monochromatic).
 Each type of lasers has single wavelength.

8. 8
Light bulb
laser

9. 9
2 – Directionality :
Depicts light being emitted from a light bulb in all directions.
All conventional light sources emit light in this manner. The
beam produced always diverges (spreads) more rapidly than
the beam generated by a laser.
Conventional light
source

10. 10
Directionality of laser
light
This Figure illustrates the highly directional nature of light
produced by a laser. "Directionality" is the characteristic
of laser light that causes it to travel in a single direction
within a narrow cone of divergence.

11. 11
3 – Coherence:
All the photons in any laser light are coherent, i.e. they are in
phase, while photons in other light sources have no relation
between them, i.e. they are out of phase.

12. 12
Incoherent light waves
Depicts a parallel beam of light waves from an ordinary
source traveling through space. None of these waves has any
fixed relationship to any of the other waves within the beam.
This light is said to be "incoherent,".

13. 13
This figure illustrates the light waves within a highly coherent
laser beam. All of these individual waves are in step, or "in
phase," with one another at every point. "Coherence" is the
term used to describe the in-phase property of laser beam.
Coherent
light waves

14. 14
4 – High intensity:
 Laser light is the intense light ever be known.
 Each laser type has its own intensity which can be defined
as the number of photons emitted per unit surface area( per
unit solid angle) .
 Even lasers with low intensity, compared with other lasers,
are intense more than the sun light.
 This property is due to huge number of coherent photons
emitted with very small angle (little divergence).

15. Properties
of Laser
Beams

17. Laser physics theory
 Electrons are found in specific energy levels of
an atom
 An electron in an atom can absorb energy from
light ( photon) or heat (phonon s)
 For light, Photons with the correct wavelength can
cause an electron to jump from the lower to the higher
energy level. The photon is consumed in this process.
 When an electron is excited from one state to that
at a higher energy level with energy difference ΔE,
it will not stay that way forever

18.  Eventually, a photon will be spontaneously emitted
when the the electron transitions to a lower energy
level which is not occupied, with transitions to
different levels. This process is called
"spontaneous emission“
The emitted photon has random direction, but its
wavelength matches the absorption wavelength of
the transition.

19. A photon with the correct wavelength to be absorbed
by a transition can also cause an electron to drop
from the higher to the lower level, emitting a new
photon.
The emitted photon exactly matches the original
photon in wavelength, phase, and direction. This
process is called stimulated emission

21. When the number of particles in one excited state
exceeds the number of particles in lower-energy
state, population inversion is achieved. In this
state, the rate of stimulated emission is larger
than the rate of absorption of light in the medium,
and therefore the light is amplified

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How to obtain a population inversion
• Molecules need to be pumped into a higher energy state.
Various methods : electrical discharge, flashlamp
excitation.
• Continuous pumping gives a Continuous Wave
(CW) Laser.
• Pulsed pumping gives a Pulsed Laser (PL)
output.

24. 3 level laser
system
• 13 transition is pumped.
• Rapid decay from 3 2.
• State 2 is metastable, excited molecules can remain in state 2 for an extended
time period, population of state 2 builds up.
• Decay from state 3 to 2 means creating population inversion between 2 and 1 .
• Laser action is possible between states 2 and 1.

25. Rapid decay
Rapid decay
LASING
E1
E4
E3
E2
•4 transition is pumped.
• Rapid decay from 4 3.
• A population inversion is produced between states 3 and 2.
• Laser action is therefore possible between 3 2.
• Molecules decay rapidly from 2 1, replenishing population of 1.
4 level laser
system

26. Classification
Lasers may be classified according to the type of
active medium, region of emitted wavelength or
mode of operation
1-According to the active medium, lasers are
classified to : solid, gas, liquid and semiconductor
lasers
 Solid lasers : Ruby laser ( aluminum oxide )
crystal (chromium doped ) ,Nd: YAG
(neodymium-doped: yttrium, aluminum garnet )
 Semiconductor –Gallium Arsenide laser ( diode
laser )
 Liquid laser : The dye material is dissolved in an
solvent, like methyl alcohol

27. Gas lasers :
 Atom :He-Ne (Helium –Neon )
 Molecule : Co2 (Carbon Dioxide ). N2( Nitrogen )
 Ion: Ar+ (Argon ion ), (Krypton ion )
2-According to the spectral region of the
emitted laser, the classification is : Ultra Violet
UV, visible and Infra Red( I.R. lasers).
3-Based on the mode of operation lasers are
classified to : continuous wave (CW), pulsed
and ultra short pulsed lasers.

29.  .
Laser Device Components
All laser devices have the basic following
components:
1-A laser medium, which can be a solid, liquid, or
gas.
2-An optical cavity or laser tube having two mirrors,
one fully reflective and the other one partially
transmissive, which are located at either end of the
optical cavity.
3-An external power source which excites or
“pumps” the atoms in the laser medium to higher
energy level


30. Laser system
Optical pumping
Electrical pumping
Chemical pumping

31. Optical amplifier .
When an optical amplifier is placed inside a resonant optical cavity, one
obtains a laser

34. These highly directional and monochromatic laser
lights can be delivered onto target tissue as a
continuous wave, gated-pulse mode, or free
running pulse mode:
Continuous waves: The beam is emitted at one
power level continuously as long as the foot switch
is pressed.
Gated-pulse mode: The laser is in an on and off
mode at periods. The duration of the on and off
timer is in microseconds.
Free running pulse mode: Very large laser energy is
emitted for an extremely short span in
microseconds, followed by a relatively long time
at which the laser is off.

35. Laser Delivery
 Articulated arms
 Hollow waveguides
 Fiber optics – for visible and near infrared lasers

36. Mode of action
Contact mode – In this type of option the distal end
of the fiber-optic is placed in direct contact with
the target tissue. Here, tactile feedback is
perceived or felt
Noncontact mode – The hand piece is held away
from the tissue and guide is provided to focus the
beam at the desired target tissue.
The operator has to adjust the focus of the beam by
varying the distance between the handpiece and
target to have the desired effect