The document discusses various phenomena of laser interaction with human tissue, including reflection, transmission, scattering, re-emission, and absorption, which lead to processes like photocoagulation and hemostatic laser surgery. Laser applications include destroying tumors, treating eye conditions, controlling bleeding, and removing unwanted tissue. Additionally, it covers photochemical ablation, which uses light to activate photosensitizers for targeted tissue destruction in oncology and dermatology.

1. LASER INTERACTIONWITH HUMAN TISSUE
When a laser is projected to tissue, five phenomena will occur:
a) Reflection
b) Transmission
c) Scattering
d) Re-emission
e) Absorption
laser transfers energy of photon to the t
Tissue because of absorption occur.

2. 1. Reflection: Laser light bounces off (hits)the tissue surface, reducing its
energy entering the tissue.
2. Transmission: Laser energy passes through the tissue.
3. Scattering: The laser light spreads in multiple directions within the tissue,
reducing precision.
4. Re-emission: Absorbed energy is released by the tissue, often as heat or
light.
5. Absorption: Tissue absorbs the laser energy, this energy is then converted
into heat .

3. PHOTOCOAGULATION
• A laser heating of tissue above 50 c and below 100 C induces disordering of
proteins and other biomolecules, this process is called photocoagulation
• When lasers are used to photocoagulate tissues during surgery, tissues become
cooked.
• They shrink in mass because water is expelled
• The heat region change color and loses its mechanical integrity
• Cells in this cooked region die and this region is called photocoagulation burn

4. APPLICATION OF PHOTOCOAGULATION
• Destroy tumors.
• Treating various eye condition like retinal disorder caused by diabetes.
• Ophthalmology
• Dermatology
• Oncology
• Gastroenterology .

5. HEMOSTATIC LASER SURGERY
• Is a medical procedure that uses laser energy to control bleeding by sealing
(blocking ) blood vessels during or after surgery .
• The laser generates heat that cause b.v to coagulate , seal and reduce blood loss .
• Application
• Ophthalmology treating retinal disorders and reducing intraocular bleeding .
• ENT ( ear , nose and throat )

6. PHOTOVAPORIZATION
• Is technique that uses laser energy to remove unwanted tissue by converting directly from
solid to Gase .
• The laser light generates high heat that breaks the cellular structure and cause tissue to
disappear , this allow doctors to remove unwanted tissue with out minimal effecting the
healthy surrounding tissue .
• Application
• Benign prostatic hyperplasia
• Removal of warts and e.t.c 4

7. the laser has high power density, it will quickly heat the tissue
to above 100 c, water within the tissues boils and evaporates
Since 70% of the body tissue is water , the boiling changes
the tissue into gas
The phenomenon is called photo-vaporization
This phenomenon can be used for

8. PHOTOCHEMICAL ABLATION
• Is a medical procedure that uses light energy in combination with photosensitive substances to
treat abnormal conditions .
How it works
 photosensitizing drug is administered to the patient and will accumulate in the abnormal tissue .
 after period time the tissue exposed to light with specific wavelength usually from laser .
 The light activates the photosensitizers causing chemical reaction that destroys target tissue .
some chemical bonds can be broken without causing local heating
This results in clean-cut incision

9. APPLICATION
 oncology
Cardiovascular medicine
• atherosclerosis removal of plaque from arteries .
 dermatology
• acne treatment
• Psoriasis and vitiligo