Page 88 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
● Since IPL systems have a wide range of wavelengths across the visible spectrum the light energy can be deposited throughout the full thickness of the skin in most cases.
● However, if the user decides to filter out some of the shorter wavelengths then the energy may mostly be absorbed in the deeper regions of the dermis rather than the superficial layers.
● This can be achieved by filtering out the blue, green and yellow wavelengths, leaving mostly red light. This is how we can choose to destroy deep target tissues while leaving the upper tissues relatively untouched.
Effect of Spot Diameter
• The penetration depth of light into the skin can also be affected by the spot diameter of the beam (for lasers and IPLs).
• At this point we should point out that the standard definition of ‘penetration depth’ is a physics concept – it is determined by finding the depth at which the value of the energy has dropped to a certain value (usually 50% or 36.8%).
Skin surface
Figure 49: Scattering causes the light beam to ‘spread out’ thereby reducing the fluence. The red lines show how the photons may spread after entering the skin. The solid red areas above show where a ‘useful’ fluence exists within the skin. It is clear that a larger spot size at the skin surface results in a deeper ‘useful zone’ where the desired reactions may still occur. Smaller diameter spots result in shallower zones. (The above fluences are the same in both spot sizes). (Image courtesy of Caerwyn Ash – Effect of wavelength and beam width on penetration in light-tissue interaction using computational methods)
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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