Page 56 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Where do the photons go in the skin?
When photons (light) enter the skin they can undergo only two processes – absorption or scattering. Once a photon is absorbed, its energy is ‘gained’ by the absorbing site, usually resulting in a rise in the local temperature.
This may be a melanosome in the epidermal basal layer (see Figure 21 – ‘Epidermal absorption’). This absorption will transfer the photon’s energy into the melanin and raise its temperature (by a very small amount!)
More likely, the photons will scatter throughout the dermis as they ‘bounce’ off many atoms (this can be anywhere between 1 and several million atoms!!).
Figure 21 – Absorption and scattering in the skin – the red arrows represent individual photons
This is because the likelihood of being absorbed in relatively low in most parts of the dermis, until the photons encounter something which ‘wants’ to absorb them strongly – like blood or melanin or another chromophore. (Note: all absorption/scattering events are probabilistic – the chances of the photon being absorbed or scattered depends entirely on the optical ‘relation’ between the photon’s wavelength and the absorption/scattering coefficients of the atoms it encounters in its travels). ________________________________________________________________________ 56
Chapter 3 Laser/IPL Hair Removal
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