Page 75 - An Introduction to Laser Tattoo Removal

Chapter 2 – Fundamentals of Laser Tattoo Removal v1.0
Laser Tattoo Removal – how it works
So, how does this treatment work? Well, the processes are still not fully understood and more work is currently underway to attempt to explain it (including by Mike!).
The Physics
In laser tattoo removal we utilise the energy of laser light to generate heat in the target ink particles within the skin. In essence, we use light energy to induce heat energy in the ink particles/aggregates – it’s merely a ‘transference’ process! What is ‘absorption’?
Laser energy is used simply because a useful amount of energy can be transferred in a suitably short time. A similar amount of energy may be transferred over a much longer period of time (say, a few milliseconds) but this would allow sufficient time for some of the induced heat energy to conduct, or, spread out, from the target ink DURING the pulse. Therefore, a suitably high peak temperature could not be achieved, since the conduction would prevent it. (Mike presented a report to the British Medical Laser Association conference in May 2021. Watch his presentation here.)
So, using a very short-pulsed laser allows us to input the required energy in a time short enough to reduce conduction to a minimum. This is why picosecond lasers were developed, since their pulses are even shorter than nanosecond laser outputs (which should, therefore, induce an even higher temperature rise on the ink particle surfaces).
Research has indicated that very high peak temperatures are required to induce the desired reaction in tattoo inks. But it is thought that this heat energy induces the photomechanical reaction and, hence, the desired outcome. (Although, this may not be the case...)
The Biology
Tattoo pigment resides at various depths within the dermis (there is no ink in the epidermis). Since the photomechanical process occurs when light is absorbed by the ink, the ink is essentially removed in a layer-by-layer process (figure 34) since the light cannot reach underlying ink.
Hence the number of treatment sessions required by a tattoo will depend how ‘thick’ it is, and how deep it is. Thicker tattoos will require more sessions than ‘thinner’ tattoos. This feature is determined by the tattoo artist – some use a ‘heavy handed’ approach with a lot of ink, while others are much more gentle in their approach. Unfortunately, it is not possible to determine the thickness of tattoo by standard visual inspection alone!
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Chapter 2 LEVEL A Laser Tattoo Removal
© The Laser-IPL Guys, 2021