Page 27 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Device
Wavelength (nm)
Absorption (cm-1)
1064
50
Nd:YAG
808 - 810 129
600 - 1200 122
1200 32.7
Table 3 - Absorption Coefficients at various wavelengths
If we take an average for IPL wavelengths, the absorption coefficient is 122 cm-1 (when using the range 600-1200nm) – very similar to that of the diode laser at 129 cm-1. Table 3 shows us that the alexandrite laser is the most strongly absorbed wavelength (755nm) in melanin, whereas the Nd:YAG wavelength (1064nm) is the weakest. This means that higher fluences must be used with Nd:YAG lasers to achieve the same results as an alexandrite laser.
Skin Colour and melanin concentration
The Fitzpatrick Scale is used across the world to describe skin ‘colour’ – but this is a mistake. Dr Fitzpatrick (a Californian dermatologist) created his scale to determine the likelihood of a patient developing skin cancers, based on their reaction to the sun’s ultraviolet energy. It was never intended to be a ‘skin colour’ scale.
A much better way to describe skin colour is to look at the concentration of melanin in the epidermis. Steve Jacques (an American laser-tissue scientist) devised a scale which does precisely this. He determined that we can describe the colour of skin by the concentration of melanin, as follows:
Diode
755
164
Alexandrite
IPL (averaged)
600
365
IPL
IPL
Skin Colour
Melanin Concentration
1
Up to 10%
2
10 – 16%
3
16 – 23%
4
23 – 33%
5
33 – 43%
6
More than 43%
Table 4 - Melanin concentration scale
________________________________________________________________________ 27 Chapter 3 Laser/IPL Hair Removal
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