Page 172 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Let’s assume, for simplicity, a spot size of 1 cm2. Then a 5000W laser will deliver 10 J/cm2 in 2 ms, while a 500W laser will deliver the same fluence in 20 ms.
The longer pulsewidth means that more of the heat energy will dissipate DURING the pulse – but that is not so important since we want heat to dissipate out to the stem cells!
This difference in power merely changes the maximum temperature attained in the hair shaft melanin. Such high temperatures can lead to rapid steam formation inside the follicle, particularly in telogen hairs, which can force the hair shaft to be ejected during treatments. Anecdotal evidence shows that such hairs may be simply ‘wiped’ away from the skin using a tissue or cloth. However, this does not guarantee a successful outcome since many of the follicle’s stem cells may survive this exposure.
Long-pulsed Alexandrite Laser – Threshold fluences
The threshold at the skin surface for this laser is approximately 9.4 J/cm2, assuming a 10ms pulsewidth.
Body area
Threshold fluence (J/cm2)
Upper lip
9.4
Chin/arms
16.8
Arm pits/legs
19.2
Bikini
22.4
Table 31 - Threshold fluences for Alexandrite lasers
The Alexandrite wavelength (755nm) is more strongly absorbed by melanin than the other lasers. Only the lower wavelengths of IPL systems are more strongly absorbed. This makes the Alexandrite laser very useful for hair removal, but it also poses a higher risk due to the higher absorptions. Careful and appropriate cooling must be applied to ensure minimal epidermal damage. In addition, the Alexandrite laser should not be used of darker skin tones – this will inevitably induce unwanted damage.
During a training exercise, Mike successfully applied a fluence of 44 J/cm2 to a skin tone 2 – with no damage to the skin (using a well-known laser unit). Of course, he used ice packs to pre-cool the skin for two minutes prior to applying the laser energy, and then again for two minutes after, to remove excess heat energy. The trainee said she felt a pain level of around 4 out of 10, and suffered no unwanted effects post-treatment.
________________________________________________________________________ 172 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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