Page 84 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
 It then takes around eight minutes to reach the Earth, whereupon it might reflect off a table surface, ricochet off the inside of your left nostril and end up in Beijing before you can say “Top o’ the mornin’ to ya!!” (With thanks to Tom Lister!)
Dermal scattering:
Laser spot
Figure 45: Scattering in the skin
In this photo, a low-powered pointer laser is directed onto Mike’s arm skin. You can see a relatively large ‘spot’ emanating from the skin with a more intense ‘spot’ in the centre.
The ‘halo’ around the central spot is generate by light scattering off the atoms and molecules in the skin. It is clear that some photons ‘travel’ quite far inside the skin before emerging, at some distance from their entry points. This is because the dermis is a highly scattering medium in the visible part of the spectrum.
   Scattering has a very important effect on the fluence as light propagates into the skin. As a beam of light penetrates into the skin, the scattering effects cause its effective diameter to increase with depth. Consequently, the fluence drops (since it depends on the spot size). So, whereas the initial fluence at the skin surface may have been set to 5 J/cm2, at some depth this will drop to 2 J/cm2.
Now, if the target you are trying to treat requires a minimum of 3 J/cm2, then it will not be affected at that depth, since the fluence is too low! Neither will all the other targets deeper than that.
 Scattering is a very important process which should be understood by all laser/IPL operators.
It can have a very noticeable effect on treatments!
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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