Page 88 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Now, if the treatment needs a minimum fluence of 4 J/cm2 to ensure sufficient cooking of the germ cells, then this treatment will not be very successful since most of the follicle is below the 4 J/cm2 level!
To get around this problem, we increase the fluence at the surface - on the right side of the image the applied skin surface fluence is now 10 J/cm2. So, the depth at which the fluence fell to 4 J/cm2 in the previous situation, the fluence is now 8 J/cm2. Similarly for the two deeper cases.
Now, the 4 J/cm2 is much deeper than previously. In this case, the treatment may well be much more successful, since the 4 J/cm2 is significantly deeper than before. This example shows that higher fluences at the skin surface will deliver more energy to deeper levels, thereby increasing the likelihood of success.
BUT.... It must always be remembered that more surface cooling MUST be applied when more fluence is applied. ALWAYS!!!
Please note – in the above discussion the numbers are not ‘real’!!! Our calculations have found that the required fluences are higher than those suggested above! Plus, the fluence distribution within the skin is quite complex – it depends on many factors including the absorption and scattering characteristics of the skin layers. Generally, the drop in fluence is exponential, not linear, after a certain depth (See Chapter 1 for more on this topic).
Fluence and Skin Cooling
We discussed skin cooling in Section 3.1, but here we will show the ‘balance’ that should be strived for when considering fluence, and skin cooling.
Figure 42 – Pain and skin damage will result from too much fluence and insufficient cooling
In essence, we are trying to heat the follicle germs cells such that they are cooked, irreversibly, to kill the follicle. This requires a sufficient amount of heat energy to be applied to the germ cells, which, in turn, means that a lot of excess energy is looking to go somewhere!
We must mitigate against this extra heat energy by applying a sufficient level of skin surface cooling.
If too much fluence is applied, without the appropriate level of skin cooling, then excess heat will raise the temperatures of the epidermal basal melanin, which will flow towards the thermal pain receptors in the upper dermis.
________________________________________________________________________ 88 Chapter 3 Laser/IPL Hair Removal
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