Page 119 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
The ‘pulsewidth’ is also known as the ‘pulse length’ or the ‘pulse duration’ – they all describe how long the light energy is ‘ON’ for, and is usually referred to as the ‘ms’ or ‘milliseconds’ when discussing laser/IPL hair removal, by many operators. Just as with most ‘cooking’ devices, the longer the pulsewidth, the more cooking will occur. So, with many laser/IPL devices, a longer pulsewidth will deliver more light energy into the target. Consequently, longer pulses usually means higher temperatures.
But, it’s not quite as simple as that. It really depends on whether the device being applied to the skin is ‘continuous’ or ‘pulsed’. In the simplest scenarios, the following tends to be true:
Device
Diode laser
IPL
Delivery Result
Continuous/Pulsed
Longer pulsewidths usually mean higher fluences resulting in higher temperatures when applied to the skin – if the light energy is ‘semi-continuous’. Diodes are generally not the same as the other technologies. But, if the energy is pulsed, then longer pulses can result in lower peak temperatures!!
Pulsed
IPL systems can deliver the energy over a range of pulsewidths. Shorter pulses, for any given fluence, will result in higher maximum (peak) temperatures in the target since a longer pulse allows more time for the heat energy to conduct from the absorbing target, during the pulse.
Nd:YAG
Alexandrite
Pulsed
Like IPLs, the pulsed output from a long-pulsed Nd:YAG laser will generate lower temperatures when longer pulses are used.
Pulsed As with the IPL and Nd:YAG technologies.
So, pulsed laser/IPL systems typically generate higher maximum temperature in the hair when shorter pulses are used, whereas continuous lasers (including diodes) are the opposite. This is discussed on more detail in Section 3.4.
Results from our computer modelling has shown that the temperature of the hair shaft is not so important when considering the temperatures in the surrounding stem cells. The hair shaft melanin heats up rapidly when hit by a high intensity light pulse of energy.
________________________________________________________________________ 119 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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