Laser” is an acronym for light amplification by stimulated emission of radiation. A laser is created when the electrons in atoms in special glasses, crystals, or gases absorb energy from an electrical current or another laser and become “excited.”Characteristics ,working ,types and application of lasers exclusively in medicine and biology.
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Laser characteristics as applied to medicine and biology
1. LASER CHARACTERISTICS AS
APPLIED TO MEDICINE AND
BIOLOGY
Karolinekersin E
Assistant professor
School of Engineering
Avinashilingam institute of home science and higher
Education for women
3. Laser
• Laser, a device that stimulates atoms or molecules to
emit light at particular wavelengths and amplifies that
light, typically producing a very narrow beam
of radiation.
• The emission generally covers an extremely limited
range of visible, infrared, or ultraviolet wavelengths
5. History of laser
• 1917-Albert Einstein lays the foundations for laser
technology when he predicts the phenomenon of
“Stimulated Emission,” which is fundamental to the
operation of all lasers.
• 1939-Valentin Fabrikant theorizes the use of stimulated
emission to amplify radiation.
• 1950-Charles Townes, Nikolay Basov, and Alexander
Prokhorov develop the quantum theory of stimulated
emission and demonstrate stimulated emission of
microwaves.
6. Contd…
• 1959-Columbia University graduate student Gordon
Gould proposes that stimulated emission can be used to
amplify light.
• 1960-Theodore Maiman builds the first working
prototype of a laser at Hughes Research Laboratories in
Malibu, California.
• This laser uses synthetic ruby as the active medium and
emits a deep red beam of light with a wavelength of
694.3 nm.
7. Contd…
• The first application for the ruby laser was for military
range finders and is still used commercially for drilling
holes in diamond because of its high peak power
• 1963-The Carbon Dioxide (CO2) laser is developed by
Kumar Patel at AT&T Bell Labs. The CO2 laser has much
lower cost and higher efficiency than the ruby laser.
8. Einstein theory for lasers
• Atom composed of a nucleus and electron cloud
• If an incident photon is energetic enough, it may be
absorbed by an atom, raising the latter to an excited state.
• An excited atom can be revert to a lowest state via two
distinctive mechanisms
Spontaneous Emission
Stimulated Emission
9. Basic components of laser
• Lasing material (crystal, gas, semiconductor, dye, etc...)
• Pump source (adds energy to the lasing material , e.g.
flash lamp, electrical current to cause electron collisions,
radiation from a laser, etc.)
• Optical cavity consisting of reflectors to act as the
feedback mechanism for light amplification
10. Working
• Electrons in the atoms of the lasing material normally reside
in a steady-state lower energy level.
• When light energy from the flashlamp is added to the atoms of
the lasing material, the majority of the electrons are excited to
a higher energy level -- a phenomenon known as population
inversion. This is an unstable condition for these electrons.
• They will stay in this state for a short time and then decay
back to their original energy state. This decay occurs in two
ways:
spontaneous decay
stimulated decay
.
11. • Spontaneous decay - the electrons simply fall to their ground
state while emitting randomly directed photons;
• stimulated decay -- the photons from spontaneous decaying
electrons strike other excited electrons which causes them to
fall to their ground state
• This stimulated transition will release energy in the form of
photons of light that travel in phase at the same wavelength
and in the same direction as the incident photon.
12. • If the direction is parallel to the
optical axis, the emitted photons
travel back and forth in the optical
cavity through the lasing material
between the totally reflecting
mirror and the partially reflecting
mirror.
• The light energy is amplified in
this manner until sufficient energy
is built up for a burst of laser light
to be transmitted through the
partially reflecting mirror..
13. Classification of lasers
Lasing medium
• Solid state lasers
• Liquid lasers
• Dye lasers
• Gas lasers
Wavelength
• UV lasers,
• visible lasers
• IR lasers
14. Solid state lasers
• Solid state lasers have lasing material distributed in a
solid matrix.
• e.g., the ruby or neodymium-YAG (yttrium aluminum
garnet) lasers.
• The neodymium-YAG laser emits infrared light at 1.064
micrometers.
15. Gas lasers
• Gas lasers (helium and helium-neon, HeNe, are the
most common gas lasers) have a primary output of a
visible red light.
• CO2 lasers emit energy in the far-infrared, 10.6
micrometers, and are used for cutting hard materials.
16. Excimer lasers
• Excimer lasers (the name is derived from the
terms excited and dimers) use reactive gases such as chlorine
and fluorine mixed with inert gases such as argon, krypton, or
xenon.
• When electrically stimulated, a pseudomolecule or dimer is
produced and when lased, produces light in the ultraviolet
range.
17. Dye lasers
• Dye lasers use complex organic dyes like rhodamine 6G in liquid
solution or suspension as lasing media.
• They are tunable over broad range of wavelengths.
18. Semiconductor lasers
• Semiconductor lasers, sometimes called diode lasers, are
not solid-state lasers. These electronic devices are generally
very small and use low power.
• They may be built into larger arrays, e.g., the writing source in
some laser printers or compact disk players.
19. Interaction of lasers
The physical processes involved in the interaction of a
laser beam and a material are divided into three parts
(1) absorption of some of the laser beam energy.
(2) transformation of this energy into chemical energy
and/or into heat, and diffusion of heat away from the
irradiated zone.
(3) eventually, chemical reaction and/or phase
transformation .
21. Absorption and reflection
• When a laser beam hits the surface of any material, one part,
R, of its energy is reflected, while the rest penetrates into the
material and is absorbed and/or transmitted.
• It is the absorbed energy that determines the behaviour of the
irradiated material.
• The value of R is given by the nature of the irradiated matter.
It depends on the wavelength, λ, of the incoming light.
• For transparent media, given the refractive indexes of the
incoming (n0) and irradiated media (n1), the reflectivity of the
interface at normal incidence is given by the well known
formula
22. contd..
• In medical applications, only the absorbed light is useful. The
light is absorbed either by water in the tissue or by some other
absorber, called a chromophore.
• The chromophore is generally either haemoglobin or melanin.
• When a light beam of intensity I0 hits a medium of thickness
d, the intensity I at the output of the medium is give
where α is the absorption coefficient
and
α−1 is the absorption length.
23. Contd..
• The absorption length is a measure of the thickness
where the light energy is transferred to the irradiated
medium.
• The smaller is the absorption length, the smaller the
transformed zone. So, well localized treatments are
possible when the absorption length is very short.
24. Diffusion of heat
• In general, light absorption takes place via electronic
excitation. The excited electrons are unstable.
• They decay by giving their energy to the lattice. This results in
the heating of the irradiated material.
• The transformation from light to thermal energy is very rapid .
• Hence the laser-heated zone corresponds exactly with the
irradiated one.
25. • Now, the heat diffuses in the material at a rate
determined by the nature of the irradiated material.
• When heat diffusion is the major mechanism, the
characteristic heat diffusion length, LD, is given by
where D is the heat diffusivity (in cm2 s−1) and t is the diffusion time
26. Thermal effects
• When the light energy is absorbed, various effects take place,
depending on the wavelength, the laser fluence and the nature
of the irradiated material.
• The most used effect is thermal heating of the irradiated
material.
• In this case, when heat diffusion is negligible, the absorbed
energy is the sum of the thermal energy necessary to heat the
irradiated volume to the transformation temperature plus the
latent heat of transformation
27. Electromagnetic effects
• When the laser fluence is very high, the electric field may attain the
order of magnitude of the electric field present within the molecules.
This electric field is in the range 107 to 1012 V m−1 .
• In this case breaking of chemical bonds and ionization take place,
leading to the well known electric breakdown of the medium.
• This breakdown results in various effects. One of them is the
creation of a shock wave.
• This is the origin of the sound emitted during air or gas breakdown.
28. contd..
• In biological (and other) materials, the plasma (ionized
gas) expands rapidly, giving rise to an electroacoustic
shock wave. This is able to destroy solid grains
• The electric field ε associated with a laser beam of power
P
where r is the radius of the laser beam,
µ0is the vacuum permeability
c is the velocity of light
29. Laser diagnostics and treatment
• Treatment cover everything from the ablation of tissue
using high power lasers to photochemical reaction
obtained with a weak laser.
• Diagnostics cover the recording of fluorescence after
excitation at a suitable wavelength and measuring
optical parameters
30. Biological effects of lasers
• Laser light waves penetrate theskin with no heating
effect, no damage to skin & no side effects.
• Laser light directs bio stimulative light energy to the
body’s cells which convert into chemical energy to
promote natural healing & pain relief.
• Stimulation of wound healing
– Promotes faster wound healing/clotformation
–Helps generate new & healthy cells & tissue
31. • Increase collagen production
–Develops collagen & muscle tissue
• Increase macrophage activity
– Stimulates immune system
• Alter nerve conduction velocity
– Stimulates nerve function
33. contd..
• Direct effect
occurs from absorption of photons
• Indirect effect
produced by chemical events caused by
interaction of photons emitted from laser and the tissues
34. Lasers in surgery
Laser surgery is a type of surgery that uses special light beams
instead of instruments for surgical procedures. Laser light can be
delivered either continuously or intermittently and can be used
with fiber optics to treat areas of the body that are often difficult
to access.
• To remove tumors
• To help prevent blood loss by sealing small blood vessels
• To seal lymph vessels to help decrease swelling and decrease the
spread of tumor cells
• To treat some skin conditions, including to remove or improve
warts, moles, tattoos, birthmarks, scars, and wrinkles
35. Carbon dioxide (CO2) lasers
• Carbon dioxide (CO2) lasers can remove a very thin layer
of tissue from the surface of the skin without removing
deeper layers.
• The CO2 laser may be used to remove skin cancers and
some precancerous cells.
36. Neodymium:yttrium-aluminum-garnet
(Nd:YAG) lasers
• Neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers can
penetrate deeper into tissue and can cause blood to clot
quickly.
• The laser light can be carried through optical fibers to reach
less accessible internal parts of the body.
• For example, the Nd:YAG laser can be used to treat throat
cancer.
37. Laser-induced interstitial thermotherapy
(LITT)
• Laser-induced interstitial thermotherapy (LITT) uses lasers to
heat certain areas of the body.
• The lasers are directed to areas between organs (interstitial
areas) that are near a tumor.
• The heat from the laser increases the temperature of the
tumor, thereby shrinking, damaging, or destroying the cancer
cells.
38. Argon lasers
• Argon lasers pass only through superficial layers of tissue
such as skin.
• Photodynamic therapy (PDT) uses argon laser light to
activate chemicals in the cancer cells.
39. Medical lasers-Low power diode lasers
BioScan – 670 nm/70 mW for superficial applications
• The energy of a red light-emitting laser is absorbed in
superficial layers of skin and tissue (penetrating to less than
1 cm).
• A 70 mW output provides a sufficient power reserve to
achieve biostimulating effects.
Most suitable for:
• Corrective dermatology,
• Cosmetology,
• Aesthetics,
• Plastic surgery and surgery
41. BioScan – 830 nm/450 mW for deep-seated
applications
• An infra-red laser is an ideal tool for the irradiation of deep-
seated tissue structures.
• A high power output makes even the most demanding
pathologies treatable in a relatively short time.
• A simultaneously irradiated red-laser pilot beam provides
exact control over the treated area.
Most suitable for:
• Physiotherapy,
• Rehabilitation,
• Rheumatology,
• Sports medicine, and
• Orthopaedics.
43. High-power 980 nm surgical laser system
Quanta – Polysurge
• A high-power 980 nm surgical laser system which can deliver optical
power up to 200 W at an output of 600 μm fibre.
• The emission mode can be pulsed or continuous. The 980 nm
wavelength has a particular characteristic: it can be absorbed in a
similar way by water and haemoglobin.
• Because tissues contain a high percentage of water, it is important
for a surgical laser to be absorbed by water to ablate tissues
properly.
• The light absorption of the same wavelength by haemoglobin is also
important for coagulation and successful haemostasis.
44. contd..
Due to the low absorption of melanin, this wavelength can
also be used for dermatological transcutaneous treatments.
Other possible application areas are removal of bladder tumors,
ureterostenosis,
• ENT
• Proctology
• Urology
• Pneumology
• Gastroenterology,
• Gynecology,
• Percutaneous laser disc decompression (PLDD),
45. contd..
• Phlebology
• General surgery
• Dermatology
• Transcutaneous treatments, etc.
• Wavelength can be 808 nm, 940 nm, or 1064 nm (Nd:YAG).
46. Medical applications of VECSEL – visible optically
pumped semiconductor lasers (OPSLs)
• In the field of dermatology, semiconductor diode lasers are
widely adopted in the areas of tattoo removal and hair
removal.
• More recently, system builders have begun to use visible
optically pumped semiconductor lasers (OPSLs) in the
treatment of pigmentation, blood vessels or wrinkles because
of the better absorption of yellow wavelengths in melanin
compared with the legacy green laser solutions.
• OPSLs have recently also been used for photocoagulation in
ophthalmology.
47. contd..
• Lasers generate up to 8 W at 532 nm, and also use a unique
yellow wavelength of 577 nm up to 5 W.
• This new yellow wavelength is exactly matched to the main
absorption peak of oxygenated haemoglobin.
• It provides a higher degree of tissue selectivity than any
previous laser wavelength.
• This delivers superior results with reduced patient discomfort
48. contd..
• Semiconductor lasers are also used in medical and
biomedical diagnostics.
• An example is the application of super luminescent
diodes in optical coherence tomography and also
in confocal microscopy
49. Laser Regulation
Lasers are classified according to the hazard
•Class 1 and 1M (magnifier) lasers are
considered safe
• Class 2 and 2M (magnifier)
emit visible light at higher levels than Class 1,
eye protection is provided
•can be hazardous if the beam is
viewed directly with optical instruments
50. • Class 3R (Restricted) Laser
Produce visible and invisible light that are
hazardous under direct viewing conditions;
• Class 3B lasers
Produce visible or invisible light that is hazardous under
direct viewing conditions
They are powerful enough to cause eye damage in a time
shorter
Laser products with power output near the upper
range of Class 3B may also cause skin burns;
51. Class 4 lasers
• High power devices capable of causing both
eye and skin burns,
• Their diffuse reflections may also be hazardous
• The beam may constitute a fire hazard
