Page 126 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
The Arrhenius Equation clearly shows that the denaturation time of germ cells is, in no way, linked to the pulsewidth – they are completely independent of each other.
However, our model also shows that the cooking efficiency is related to the pulsewidth when considering the threshold fluence. These results suggest maintaining a pulsewidth between 5 and 50 milliseconds, but ONLY if using the threshold fluences. See the next section for more on this.
Fluence
The fluence is the ‘concentration’ of the light energy on the skin surface – the energy in the spot size area (energy density). All the temperature rises in this skin are due to absorption of some of this energy by chromophores.
The choice of fluence is critical in determining a successful outcome. Most poor treatment results are directly due to insufficient fluence! There is simply not enough heating of the targets to cook the germ cells properly.
In the Section ‘Threshold denaturation fluences – four devices’ we discussed the ‘threshold’ fluences for hair treatments. These are the fluences required to just attain an Omega of 1 – irreversible cooking of the germ cells. However, this will only cook around 63.2% of the germ cells – we use this as a standard definition of ‘irreversible denaturation’ used by the scientific community.
In the real world, we wish to ensure that none of the cells can regenerate the follicle. To ensure this we should really go for a denatured volume of at least 99% - this equates to an Omega of 4.6. This is easy to achieve with all of today’s photothermal systems, if the fluence is sufficiently high.
We recommend using the following set of fluences:
Table 33 – Recommended fluences for four devices
In Table 33 we show our recommended fluences for various body areas and for the four main hair removal systems. You may notice that these are all just the threshold fluences plus 1 J/cm2 (approx.), except for the Nd:YAG fluences, where we have added 2 J/cm2. We suggest these
________________________________________________________________________ 126 Chapter 3 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2022
Device
Upper lip
Chin/arms
Arm pits/legs
Bikini
Fluence
J/cm2
J/cm2
J/cm2
J/cm2
IPL
12.5
22
25
29
Diode
12
21.5
24.5
28.5
Nd:YAG
26.5
46.5
53
62
Alexandrite
10.5
18
20
23.5