Page 69 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal
P. 69
Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Figure 23 – The five main parameters required for efficient and safe photothermal treatments
Pulsewidth
The pulsewidth determines how long the energy pulse is ‘ON’. Many people appear to be concerned about the ‘correct’ pulsewidth to choose, mainly because its effects are not properly explained.
We can think of the pulsewidth as the ‘cooking time’ of the cells. In particular, we must consider the cooking time of the real targets – the germ cells. The Arrhenius Equation tells us that we must maintain the elevated temperature of those cells for a certain amount of time to ensure irreversible denaturation (cell death).
As a direct consequence, this means that there are, in fact, an infinite number of possible combinations of temperature and time which will result in complete cell death.
The theory of Selective Photothermolysis states that the energy pulses should be less than the thermal relaxation time of the absorbing target. However, as we have shown previously, this is incorrect since it makes no allowance for the time required for the germ cells to properly cook.
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