Page 139 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Appendix 8 – Sitting on a Photon
What actually happens when we use lasers or IPLs?
Let’s look at all the various processes that may occur when we’re treating hair (or vessels or tattoos etc).
The first thing that must happen is that a new photon must be generated. This will occur when an electron, orbiting an atom’s nucleus, is ‘excited’ by another photon, or by some other external force, such as a voltage. This excited little electron jumps from its usual orbit (known as the ‘ground state’) into a higher orbit as it gains energy.
However, all good things must come to an end, and the little electron will eventually fall back into its designated orbit - as it does it will release the energy it gained during the excitation process. These images came from NASA.
At this point, a brand new photon has been generated. It now faces an interesting future...
There are a number of possible paths for this photon to take.
Case 1 - The simplest is that it enters the skin, is scattered around by various atoms in the skin, and then is absorbed by another atom. In this case, another electron will be excited by the absorption process, but, as it drops back into its natural ground state, the energy it releases is ‘felt’ as a vibration rather than a photon. This vibration is essentially heat energy. When many, many electrons de-excite, their collective vibrational energies will translate as heat energy in the absorbing medium, raising its temperature.
This is what happens in most tissue interactions. So, the melanin in hair or in the epidermis will absorb many photons and use their energy to generate heat. These photons only exist for a very short time – typically around 10 or 20 nanoseconds in total!
________________________________________________________________________ 139 Chapter 3 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2022