Page 100 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
                    Power Density
Power density describes how ‘fast’ the fluence is delivered. Short pulse durations = high power densities; long pulse durations = low power densities.
So, it describes the flow of energy density per second, concentrated into a spot diameter being delivered in the pulse duration.
Target chromophores will absorb some of the incoming light energy and may heat up as a consequence.
The main tissue reactions are:
photo-chemical, photo-thermal (Selective Photothermolysis), photo-ablation, photo-mechanical.
When a photon of light interacts with an electron around an atom, the photon’s energy can be ‘taken’ by the electron causing it to be ‘excited’ – this process is absorption.
If an electron has absorbed a photon’s energy, then it will , after a short time, fall back into its original orbit around the nucleus. As it does it releases the energy it took from the photon. If the conditions are right, that energy will emerge as a new photon – this is a scattered photon.
     Understanding the above expressions will go a long way into understanding how laser/IPL treatments work, and how to get the best out of your equipment.
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
© The Laser-IPL Guys 2021

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