Page 53 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
The shorter the wavelength, the stronger scattering i.e. blue light is scattered much more strongly compared with red light, see picture below. The implication of this phenomena is that red light can reach further into the skin compared with shorter visible wavelengths.
The optical scattering properties of skin is a quite complicated topic but there are some pretty straight forward physical models that can explain the phenomena. However, on this level you only have to be aware of the scattering effect and understand the wavelength dependency.
Figure 19 – Scattering in the clouds
The strong scattering process in the skin "dilutes" the power density of the light inside the skin which effectively limits the penetration depth of light. Compare the fact that sun light is much less intense on your skin when the sunlight is obscured even by a thin cloud.
An important factor to consider is that light scattering in skin is dependant of the colour (wavelength) of the light.
Optical scattering in human skin and its light colour/wavelength dependence. Red light reaches deeper into the skin compared with blue and green light. Note! The back scattered light is not shown in this picture. Note also that the absorbing skin chromophores is absent in this model as we only want to show how the light scattering of non-absorbing skin cells, which are in huge majority compared with the absorbing skin cells.
Penetration Depth
Penetration depth is discussed in some detail in Chapter 1 – please read that section. Here we present a short review:
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