Page 119 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Increasing the fluence – what happens?
All the fluences in the previous section are based on achieving an Omega of 1 in the germ cells – this is the Arrhenius parameter which tells us if those cells are irreversibly denatured – dead! Technically, an Omega of 1 means that 63% of the volume of those cells are dead. Those fluences are the absolute minimum required to achieve this state.
What happens to the cells if we increase the fluence? The most obvious answer is that more of the cells will be irreversibly cooked – a greater volume that 63%. So, what it this relationship between fluence and the volume of dead cells?
Using our thermal transfer model we calculated the new values of Omega for the above thresholds plus 1 J/cm2, and then plus 2 J/cm2. These are modest increases in fluence, but they reveal a very interesting outcome.
Device / fluence
Final Omega
% volume dead cells
IPL:
Threshold – 11.5 J/cm2
1.0
63.2
12.5 J/cm2
5.3
99.5
13.5 J/cm2
26.5
100
Diode:
Threshold – 11.15 J/cm2
1.0
63.2
12.15 J/cm2
5.4
99.5
13.15 J/cm2
27.9
100
Nd:YAG:
Threshold – 24.5 J/cm2
1.0
63.2
25.5 J/cm2
2.1
87.8
26.5 J/cm2
4.6
99.0
Alexandrite:
Threshold – 9.4 J/cm2
1.0
63.2
10.4 J/cm2
7.3
99.9
11.4 J/cm2
51.1
100
Table 31 – Final values of Omega when increased fluences are applied
These data reveal something very interesting, and not intuitive! A small increase in applied fluence can make a huge difference in the value of Omega, from a 63.2% damaged level to nearly 100%.
________________________________________________________________________ 119 Chapter 3 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2022