Page 105 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
In a first approximation, as the light penetrates the skin layers its intensity (fluence) drops according exponentially according to the Beer-Lambert Law (please visit this site to learn what this actually means). Hence, in essence for every light-based treatment there are at least three zones of reaction:
Figure 54 – An energy of 0.6 Joules concentrated into a 5 mm diameter spot will yield a fluence of 3.1 J/cm2
So, if we deliver 0.6 Joules (600 millijoules) of light energy into a 5 mm diameter spot, then the resultant fluence is 3.1 J/cm2.
Upper zone – In the superficial part of the skin most of the energy is absorbed by constituent tissues. Hence, most of the desired photothermal reactions will occur in this zone. If the incident energy is too high then unwanted tissue damage may also occur. This can be mitigated with proper and sufficient skin surface cooling, preferable contact-cooling (due to its higher efficiency compared with other methods) – see Figure 55. We call this the ‘Kill’ zone.
Figure 55 – Zones of the skin where reactions may, or may not, occur
________________________________________________________________________ 105 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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