Page 111 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Figure 63 - If a surface fluence of H0 is applied to the skin, then the fluences through the depth of the dermis may be calculated using a Monte Carlo model
Figure 63 shows us that the fluence down to a depth of around 1.4 mm is greater than the incident fluence at the skin surface. This is entirely due to the accumulation of forward-direction photons plus the back-scattered photons, on their way back towards the surface.
At a depth of 4mm, the incident fluence has dropped to around one quarter of its original value at the surface. This is typically the depth of the deepest follicles.
Using this data, combined with the results from the 1-D heat conduction model, we can calculate the required fluences for the irreversible thermal destruction of hair follicles down to a depth of 4mm (Table 22).
Device
Diode Alexandrite Nd:YAG IPL
Required fluence (J/cm2)
44.4 37.6 98.0 45.8
Table 22 - Required fluences to induce irreversible damage to follicles to a depth of 4mm
Interestingly, the heat conduction model also shows that the pulsewidth is not important in this process, as long as the fluence is sufficiently high. Likewise, the wavelength is also not important – it merely changes the value of the required fluence.
________________________________________________________________________ 111 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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