Page 86 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
Depth of Penetration of Light in the Skin
It is useful to know how far light energy penetrates into the skin. This depends on a number of factors including the wavelength and the spot diameter.
Effect of Wavelength
● The penetration depth is the depth within the skin which the light can reach. This is mostly determined by the wavelength of that light and the properties of the tissue.
● In the visible part of the spectrum the penetration depth increases from the blue end to the red end – in other words, blue light is absorbed near the top of the skin (which easily ‘burns’ the skin) while red light may penetrate all the way down to the fatty layer beneath the dermis. Click here for a video of this process.
          So, it’s quite obvious that the choice of wavelength is crucial – it is dictated by the depth of the target AND the absorption characteristics of that target – watch this video, or read this pdf.
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
Epidermis 0.1 mm
Dermis 2 - 3 mm
Subcutis
  Figure 47: Different wavelengths of light penetrate to different depths. Blue light does not go far into the dermis, while red and near infrared penetrates much deeper.
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