Page 94 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
penetrates deeper into the skin. Hence the fluence drops (since it’s just the energy divided by the spot diameter).
Total fluence in skin =
Reflection at skin surface
+
backscattered energy
+
bulk absorption in the dermis
+
chromophore(s) absorption
+
beam expansion (scattering)
+
transmitted energy to subcutis tissues
PA did a series of calculations in a Monte-Carlo model and found that a significant amount of the light energy will be turned through more than 90o – and a large chunk of this light will fly straight back out of the skin – we call this ‘back-scattering’. PA found that up to 60% of the light entering the skin may be back-scattered out, depending on the wavelength. (Just to confuse the matter, scattering and back-scattering, are very dependent on the wavelength of the light!)
Of the light that remains in the dermis, some of it will be absorbed by various tissue components – collagen, water, blood, bilirubin, keratin etc.
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