Page 117 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
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 28 - 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.
Long-Pulsed Nd:YAG Laser – Threshold fluences
The absorption of 1064nm light by melanin is relatively low compared with the above three devices (see Figure 55). As a consequence, a higher fluence is required from Nd:YAG lasers to achieve the same level of temperature rise in the hairs.
Body area
Threshold fluence (J/cm2)
Upper lip
24.5
Chin/arms
44.5
Arm pits/legs
51.0
Bikini
59.7
Table 29 - Threshold fluences for Nd:YAG lasers
The threshold at the skin surface for this laser is approximately 24.5 J/cm2, assuming a 10ms pulsewidth. The absorption by melanin of this wavelength is much weaker compared with the other hair removal systems. This explains why such relatively high fluences are required to achieve results. However, the absorption in the dermis is also very low which is why the Nd:YAG laser penetrates so deeply into the skin.
________________________________________________________________________ 117 Chapter 3 Laser/IPL Hair Removal
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