Page 29 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Device
Wavelength (nm)
Absorption (cm-1)
1064
50
Nd:YAG
Diode
808 - 810
600 - 1200
1200
128.5
122.2
32.7
755
160.4
Alexandrite
IPL (averaged)
600
365
IPL
IPL
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.
Using a process called ‘normalisation’ we can take the spectral output from an IPL Xenon lamp, between 600 and 1200nm, and find its ‘average’ or ‘mean’ value. Doing this shows that the mean is around 818nm, just slightly higher than most commercial diode lasers used today. The absorption coefficient for 818nm is 122 cm-1, as above.
Skin Colour and melanin concentration
The Fitzpatrick Scale is used across the world to describe skin ‘colour’ – but this is a mistake. Dr Fitzpatrick (an American dermatologist) created his scale, in 1975, 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:
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
________________________________________________________________________ 29 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2025