Page 125 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
APPENDICES
Appendix 1 - Summary of Light-Tissue Interactions
The important points to note about the way light interacts with tissues are:
Wavelength
The wavelength determines how deeply the light can penetrate It also determines how much energy is absorbed by the targets.
Energy
Energy is what does the “work” in raising temperatures in the absorbing targets.
Pulse duration
Pulse duration is the time in which the light energy is delivered. This has a strong correlation with the resulting temperature rise in the absorbers. It can be anything from picoseconds (trillionths of a second) to many seconds or minutes.
Power
Power is simply how quickly or slowly energy is delivered to the site. If the energy us delivered very quickly, then the power is ‘high’. If the same energy is delivered more slowly, then the power is lower than before. We can calculate the power by dividing the energy by the pulse duration.
Spot diameter
The spot diameter also determines how deeply the light can penetrate principally due to scattering.
Energy Density (Fluence)
A laser will generate a beam with a certain amount of energy. We can focus this energy into a small spot size using lenses. Different lenses produce different spot diameters. The ‘concentration’ of energy in the spot diameter is known as the ‘fluence’ or ‘energy density’.
Power Density
Power density is just like energy density except it all includes the delivery time or pulse duration. So, it describes the amount of energy concentrated into a spot diameter being delivered in the pulse duration.
________________________________________________________________________ 125 Chapter 3 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2022