Page 26 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Figure 2 - Melanin absorbs light from the UV (350nm) end of the spectrum up to the near infrared (NIR) part of the spectrum
Since we typically use infrared laser wavelengths, only a small amount of energy will heat up the epidermal basal layer – meaning that less thermal damage will occur there (relatively!).
This is precisely what we’re after – localised heat damage in the hair shaft while minimising the damage to the surrounding skin! If we set up our equipment properly, and apply it correctly, we should be able to thermally destroy the follicles, without damaging the skin.
Melanin and its effects on hair removal (Absorption Coefficients)
This next section is quite ‘scientific’. It explains the science behind what we’re trying to do with lasers and IPLs. It’s worth trying to get to grips with this stuff – it will help your understanding. But don’t be put off if you don’t ‘get it’ – it all helps!
We analysed of an IPL device’s output and were able to calculate the absorption coefficients for various wavelengths, and ranges of wavelengths, and compare them with those of the Nd:YAG, diode and alexandrite lasers.
We were trying to calculate the absorption coefficients of melanin at various wavelengths. This tells us how ‘strongly’ melanin will absorb these wavelengths. This is very important because they directly affect the energies we must apply. A fluence of 10 J/cm2 from a diode laser (emitting a 810nm wavelength) will not induce the same reaction as 10 J/cm2 from an Nd:YAG or an alexandrite laser, or from an IPL. This is mostly due to the different amounts of energy that the melanin will absorb. Melanin treated by an Nd:YAG laser will absorb approximately 39% of the energy emitted by a diode laser, (absorption coefficient at 1064nm = 50 cm-1; absorption coefficient at 810 nm = 129 cm-1: ratio = 50/129 = 0.39)
________________________________________________________________________ 26 Chapter 3 Laser/IPL Hair Removal
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