Page 61 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Melanin absorption – how they compare across devices?
Figure 23 – The melanin absorption curves for six skin colours
The above graphs show the melanin absorption curves for six skin colours – ST1 to ST6. These skin colours are based on the Steve Jacques epidermal concentration analysis and better reflect the optical properties of the epidermis. This is a far more accurate representation of the skin colour compared with the Fitzpatrick scale (which is, in essence, a ‘response to ultraviolet energy’ scale!)
Table 13 - The wavelengths and corresponding melanin absorption coefficients for four typical hair removal systems. Many IPL systems typically use a range between 600 and 1200nm – this equates to an absorption coefficient
of 122.2 cm-1, which is equivalent to a wavelength of 818nm.
The absorption coefficients in the table above show clearly how strongly each wavelength is absorbed by melanin (both epidermal and in follicles). The IPL range, 600 to 1200nm, is fairly typical in many hair removal treatments. Using a normalised analysis of the output spectrum of an IPL Xenon flashlamp, it is possible to calculate the “equivalent single wavelength” from the average absorption coefficient. This turns out to be 818nm – very close to the standard diode laser output used in these treatments (810 and 820nm). Interestingly, if the range 700-1200nm
________________________________________________________________________ 61 Chapter 3 Laser/IPL Hair Removal
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Device Wavelength (nm) Absorption Coefficient (cm-1)
IPL 600-1200 122.2
Diode 810 128.5
Alex 755 160.4
Nd:YAG 1064 50.4