Page 226 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
wide range of wavelengths, up to 1200nm. But, for hair removal, they are usually filtered so that only the range about 600 to 1200nm is actually utilised. Some systems also filter out the top end of this range so that they are restricted to between 600 and 900nm, typically.
Table 40 – The wavelengths output by most hair removal systems
These wavelengths are all absorbed by melanin (see Figure 122) and can penetrate deep into the dermis. (We often see online comments saying that “IPL light energy doesn’t penetrate as deeply as lasers” – this is just gibberish!). Note that there are other diode systems which may output a 900nm wavelength, plus there are some systems which combine the diode with an Alexandrite and an Nd:YAG laser, into one unit.
But the penetration depth is not the only important factor when considering wavelength. We must also think about how much of that energy will actually be absorbed by the target – follicular melanin (see below).
Wavelength (nanometres)
Diode
808, 810
Alexandrite
755
Nd:YAG
1064
IPL
400 - 1200
Figure 121 – Penetration depths of four wavelengths
Pulsewidths
Device
The pulsewidths generated by different lasers and IPLs vary widely. Many lasers are limited by the technology or engineering to relatively short pulsewidths, whereas IPLs can generate longer pulses by using ‘trains’ of sub-pulses.
________________________________________________________________________ 226 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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All of these wavelengths can penetrate deep into the dermis – the Nd:YAG penetrates about 3.5mm compared with the Alexandrite which only goes as far as 2mm.
(These are the standard physics definitions of the “1/e” penetration depths which is where the incident energy drops to about 37% of the original value.)