Page 197 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Figure 107 - Consistent placement is important in ensuring good treatment results
Why are long-pulsed Nd:YAG and Alexandrite lasers apparently ‘easier’ to use in hair removal?
In hair removal procedures, most long-pulsed Nd:YAG and Alexandrite lasers typically use short pulsewidths - usually less than 10ms, often less than 5ms. They can deliver all of their energy within these short pulses, whereas diode lasers and IPLs typically use longer pulses.
Such short pulses induce higher temperatures in the absorbing targets (melanin) in the skin, since there is less time for the heat energy to diffuse away, during the delivery of the pulse.
Hence, a diode laser delivering 10 Joules of energy in a 5ms pulse, will generate higher temperatures in a target than the same energy delivered by a diode laser in a 10 or 20 or 50ms pulse. In fact, the longer the pulse, the lower the peak (maximum) temperatures attained in the hair shafts.
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Most diodes and IPLs require longer pulses in order to deliver higher energies, compared with Alex and Nd:YAG lasers. This is simply a constraint of the technologies.
As a direct consequence, Alexandrite lasers will inevitably induce more thermal damage, for the same fluence, compared with diodes and IPLs. Given that hair removal is a photothermal process, these higher temperatures may result in 'better' clinical outcomes.
________________________________________________________________________ 197 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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