Page 20 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
The basic parameters (settings) on lasers and IPLs
We discussed the basic parameters (settings) in Chapter 1, but we will do a wee review here:
Parameters Purpose (Settings)
Wavelength
We choose an appropriate wavelength of light which we know will be preferentially absorbed by the melanin in the hairs. This tends to be at the red end of the spectrum, partly due to absorption, but mostly due to the fact that red light can penetrate more deeply into the dermis than all the other visible wavelengths!
We usually measure this in nanometres (nm). These are billionths of a metre.
Most diode lasers emit between 808 and 810nm, which are infrared wavelengths. They are invisible to the human eye, but are reasonably well absorbed by melanin.
Alexandrite lasers emit a 755nm wavelength (we call this ‘near’ infrared), which is more strongly absorbed by melanin – but about 30% more than the diode wavelengths!
Long-pulsed Nd:YAG lasers emit at 1064nm. This wavelength is absorbed the least by melanin - about 40% the absorption of the diode wavelengths. But, this has a major advantage for darker-skinned people. The relatively low absorption of this wavelength means that there is much less risk of epidermal damage in darker skins.
It also means that there is less absorption in the hair melanin too, which is why the fluences (see below) used with these lasers is typically significantly higher than with the other systems.
IPLs are not the same as the above lasers. IPLs are NOT lasers. But this doesn’t matter – they still output light energy. They emit a wide range of wavelengths, including blue, green, yellow, red and infrared.
For hair removal, we use filters to allow through only those wavelengths we require. Typically, this is in the range 600 to 1200nm (or thereabouts), which includes red and infrared light.
All of these wavelengths can be absorbed by melanin (see graph later in this book). In fact, the 600nm wavelength is much more strongly absorbed than all of the above laser wavelengths, while the 1200nm is absorbed the least.
________________________________________________________________________ 20 Chapter 3 Laser/IPL Hair Removal
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