Page 78 - An Introduction to Laser Tattoo Removal
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Chapter 2 – Fundamentals of Laser Tattoo Removal v1.0
‘converted’ into 532nm light energy using a frequency-doubling crystal, known as a KTP (potassium titanyl phosphate) crystal. Note that by doubling the frequency, we half the wavelength from 1064 to 532nm.
This is quite unusual in lasers! Most lasers cannot be ‘manipulated’ like this to generate appreciable amount so useful energy at different wavelengths. The physics demands that this can only occur with very high power densities (see Chapter 1) which explains why this frequency-doubling process can only be done with high-powered lasers such as Q-switched or picoseconds. Long-pulsed Nd:YAG lasers cannot generate a 532nm output!
But this is not a 100% efficient process. Typically, around 70% of the incident 1064nm laser energy can be converted to 532nm. Hence, when using a KTP crystal, the final output which hits the skin will contain around 70% of 532nm light and 30% of 1064nm light.
   The ‘YAG’ component of these crystals is ‘Yttrium Aluminium Garnet’. This is the ‘host’ crystal which ‘holds’ the neodymium atoms. The neodymium is the active part of this crystal – its atoms are excited by the flashlamp light energy. When the electrons fall back into their original orbits, the wavelength emitted is 1064nm.
What are the differences between these wavelengths in skin?
Today we have a choice of four wavelengths to use for laser tattoo removal. How do these compare when interacting with the skin and tattoo inks?
Let’s look at 532 nm first:
This is the frequency-doubled Nd:YAG wavelength. It is green. This suggests that it should be excellent at treating red ink. In many cases, it is, but it is not quite as simple as that.
Firstly, we should consider that the 532nm wavelength is strongly absorbed in both melanin and blood (Mike published an article on the absorption by blood vessels in the skin with all these wavelengths – except 755nm).
This can have significant effects on treatment outcomes since some of the energy may be ‘lost’ to these chromophores before racing the deeper tattoo inks. In addition, 532nm may cause unwanted effects in terms of vessel damage and natural pigment alterations.
However, the upside is that it can be used to trat benign pigmented lesions such as age and liver spots, freckles, Café au Lait, solar lentigos etc. It also strongly absorbed in ink colours such as red.
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Chapter 2 LEVEL A Laser Tattoo Removal
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