Page 57 - An Introduction to Laser Tattoo Removal

Chapter 2 – Fundamentals of Laser Tattoo Removal v1.0
(Nd:YAG; fundamental), 755 nm (alexandrite), 694 nm (ruby) or 532 nm (Nd:YAG, 2nd harmonic).
Laboratory studies have measured the absorption of wavelengths across the visible spectrum and into the near infrared region. These wavelengths are all absorbed by melanin to a certain extent (although very little of the 1064 nm energy is absorbed).
Since tattoo pigment is all located in the dermis, the laser energy must pass through the basal layer containing most of the melanin absorbing cells (melanocytes). This causes at least two effects:
1. Absorption in this layer generates heat which conducts into both the epidermis and dermis;
2. It also reduces the amount of energy available for the deeper ink particles.
Neither of these are particularly useful in the treatment process. Heating the basal layer can induce thermal damage in the epidermis quite easily, especially if excessive fluences are used. This can destroy much of the epidermis leaving behind an area where bacteria can easily access the skin.
Skin surface cooling is therefore essential following laser treatment, to minimise any such effects.
The second issue, lower energy in the dermis may interfere with the overall treatment process, leading to slow ink removal.
It is important to understand these effects and the relative importance of the wavelength chosen. The 532 nm light will be most strongly absorbed compared with the other three wavelengths. In fact, the amount of melanin absorption decreases as the wavelength increases, such that there is minimal absorption with the 1064 nm wavelength.
So, it important to consider the patient’s skin colour (or rather, their melanin content, to be precise) when choosing an appropriate wavelength. If no choice is available, then careful consideration must be given to the cooling aspects of the skin.
532nm light is the most strongly absorbed in melanin, while it also penetrates the least distance into the skin.
The table above shows the ranking order of melanin absorption and penetration depth by wavelengths. The longer the wavelength, the deeper its penetration into the dermis. However,
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Chapter 2 LEVEL A Laser Tattoo Removal
© The Laser-IPL Guys, 2021
Wavelength (nm) 532 694 755 1064
In ranking order...
Melanin absorption 1 2 3 4
Penetration depth 4 3 2 1