Page 239 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
same energy as one Joule of IPL energy. The fact that the energy is spread amongst a range of wavelengths is not that important. In fact, the range of wavelengths simply means that the heating process will vary along the length of the hair, with more heating occurring nearer the skin surface.
However, there are no studies – clinical or theoretical – which shows any significance to this distribution of heating.
There are probably more myths out there – please let us know if you come across any. We’ll be happy to dispel them.
When light enters the skin it begins to scatter almost immediately (See ‘Where do the photons go?’). This occurs when the photons interact with atoms in the stratum corneum. The likelihood of scattering is much greater than the likelihood of absorption. When a photon scatters, it inevitably changes direction from its original path.
As a consequence, all the photons spread out in all directions. Now, the three defining properties of laser light is that it is monochromatic (single wavelength), highly coherent and minimally divergent (see Chapter 1). Once the laser photons start to scatter, they lose their coherence rapidly and diverge all over the place! The only remaining property is the monochromacity – but even this will change if the scattering events are inelastic (losing energy making the photons ‘redder’).
So, it could be argued that ‘laser’ light stops being ‘laser’ when it starts to scatter! It then resembles ordinary light except that it is a single wavelength (colour)...
________________________________________________________________________ 239 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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