Page 57 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
At some point a photon may be absorbed in the dermis (see Figure 21 – ‘Dermal absorption’).
If it not absorbed by an atom in the dermis, it may continue its ‘random walk’ through the dermis until it reaches the deeper, fatty layer – where it may be absorbed by an atom there. This process is known as ‘transmission’ since the photon is lost to the dermis (see Figure 21 – ‘Transmission’).
Conclusion
The ‘cooking’ times and the ‘cooling’ times (TRT) of cells are independent of each other. There is no direct relation between them. Using the cooling times of targets to determine the most appropriate cooking times is simply wrong.
Further, the cooking times are hugely dependent on the local temperatures. So, using very short, high fluence pulses can achieve exactly the same end result as a longer, lower fluence pulse. It is the combination of fluence and pulse duration that is important – however, these two scenarios may have a significant difference in terms of unwanted, collateral damage.
So, we should not use the TRTs of tissue targets to determine the appropriate pulse duration. After all, nobody ever chose the baking time for a cake based on how quickly it cools!!
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