Page 115 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
level! If your fluence is above the threshold, even by only 1 or 2 J/cm2, the importance of the pulsewidth is greatly reduced.
FLuence (J/cm^2)
30 28 26 24 22 20 18 16 14 12 10
Threshold fluences - IPL
Upper lip
Chin Arms Legs
Arm pits
Bikini
Figure 55 - Threshold fluences required to treat a range of body sites for IPL systems
We have also assumed a wavelength range between 600 and 1200 nm in these calculations. A smaller range will require higher fluences. Obviously, deeper follicles (bikini, armpits) require more fluence at the surface to ensure sufficient light gets deep enough to heat them. This means that more pre-cooling is also required, to protect the epidermis (since it will also get hotter!!).
Body area
Threshold fluence (J/cm2)
Upper lip
11.5
Chin/arms
20.8
Arm pits/legs
23.9
Bikini
27.9
Table 26 - Threshold fluences for IPLs
The threshold at the skin surface for IPL devices is approximately 11.45 J/cm2, assuming a 10ms pulsewidth and a wavelength range from 600 to 1200nm. At this fluence the final value of Omega is 1 meaning that the cells are irreversibly denatured – these hairs cannot regrow.
Interestingly, a small increase in fluence (i.e. 1 J/cm2) above these threshold makes a large difference in terms of cell destruction! But, fluences below these levels will merely cook some of the stem/germ cells, meaning that finer hairs will likely grow back in the future, due to the surviving germ cells.
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