The essential elements of lasers that determine its interaction with matter are as follows:
  1. Wavelength
  2. Power density
  3. Temperature
  4. Pulse rate and duration
  5. Delivery system   

Laser Beam Interact with tissues in four ways

A portion of the incident beam may be reflected on the surface without penetration   or interaction with tissues.

A portion of the light may be transmitted through the tissues unattenuated.

A portion of light may be absorbed by the tissues.

Remaining light may penetrate the tissues and be scattered without producing noticeable effect. 

The extent of the interaction will be proportional to the wavelength of absorption of the particular wavelength by tissue. Tissue elements that exhibit a high co-efficient of absorption for particular wavelength or speed of light energy are called chromophore. 

Tissue effects of laser irradiation

When laser is absorbed by tissue four types of reaction occurs:
  1. Photochemical
  2. Photothermal
  3. Photomechanical
  4. Photoelectrical  

Photochemical  Interaction

Photochemical interaction includes biostimulation which describes the stimulatory effects of lasers on biochemical and molecular process that normally occur in tissues such as healing and repair. 

 

PHOTOCHEMICAL  INTERACTION
 

Photothermal Interaction

 
In Photothermal interaction laser light energy absorbed by the tissue substances and molecules becomes transformed into heat energy which produces the tissue effect. Thermal effects are largely wave length dependent because the amount of heat generation in tissues is determined by   extent of preferential absorption of beam.   

Photomechanical and Photoelectrical Interaction

Photo disruption, photo dissociation, photo Plasmolysis, photo acoustic are used to describe mechanical and electrical interaction.  
 
PHOTOMECHANICAL AND PHOTOELECTRICAL INTERACTION

 

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