Page 97 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
Tissue Reactions – Chemical, Thermal, Ablative & Mechanical
When tissue or cells absorb light energy (from lasers or IPLs) there are four basic reactions which may occur:
 Photo-chemical
This type of reaction cannot be sensed in any way. There is no ‘heating’ or sound generated during this process. The reaction is basically a chemical one inside cells. Typically, lower powered (non-thermal) lasers and LED systems are used to stimulate such reactions.
 Photo-thermal
If the energy is ‘turned up’ and a heating process begins, then the reaction is deemed to be ‘thermal’. In other words, the cells or tissue temperature will rise appreciably. This may cause thermal damage if the heating is applied for a sufficiently long time.
   Photo-ablation
Ablation usually describes the process of ‘boiling’ where tissue/cells are physically separated from their surroundings. This usually occurs with lasers such as carbon dioxide (CO2) or erbium:YAGs. These systems raise the temperature of the tissues to above 100°C where water boils.
 Photo-mechanical
If the laser energy is absorbed by a target chromophore is a very short time (typically billionths of a second, 10-9 s), then the temperatures may reach more than one thousand degrees Celsius. This causes a ‘mechanical’ reaction in the targets which usually results in a physical disruption of some kind. This occurs in laser tattoo removal where the ink particles become extremely hot (for a very short time) and cause a physical rupturing of the fibroblast cells which contain them.
Note that ‘photo-mechanical’ is often called ‘photo-acoustic’ too!
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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