Page 91 - Chapter 3 - An Introduction to Laser/IPL Hair Removal
P. 91
Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
We must always remember that the end-goal is to denature the germ cells. They are not near the hair (relatively speaking!) The heat energy MUST conduct from the hair to the follicle wall when the germ cell bulge is located. This takes some time – our calculations reveal that it can take between approximately 57 and 91 milliseconds for the germ cells to reach their maximum temperatures after the pulse has stopped.
Pulsewidth
Peak temperature achieved at time
Delay between end of pulse and peak temp
0.1
91.4
91.3
1
91.9
90.9
10
96.5
86.5
50
120.5
70.5
100
156.7
56.7
Table 21 – Times when the germ cells reach their maximum temperatures (all in milliseconds)
The table above shows that the maximum (peak) temperatures in the germ cells are attained a significant time after the pulses have stopped heating the hair shafts. In fact, there is little resemblance between the pulsewidths and the timings of the peak temperatures. This appears to show that the pulsewidths are only really important when determining the peak temperatures of the hairs, but don’t really have much influence over the timings in the germ cells.
Our research shows that the fluence has a more significant influence on the outcome than the pulsewidth. Once that threshold fluence has been exceeded, the pulsewidth becomes less important. As the fluence increases above the threshold, the influence of the pulsewidth becomes less relevant.
This indicates that we should probably focus more on the applied fluence rather than the pulsewidth when treating hair – whilst keeping the pulsewidth within ‘safe’ limits. Too long a pulse will inevitably cause unwanted damage to the adjacent tissues.
At present, our results show that keeping the pulsewidth in the range from around 5 to 50 ms is a ‘safe zone’ – a supra-threshold fluence will always successfully denature the germ cells. Again, we should remember that the fluence has an upper limit too – otherwise damage is likely.
As fluence is increased, the importance of pulsewidth diminishes
________________________________________________________________________ 91 Chapter 3 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2022
