Page 86 - An Introduction to Laser Tattoo Removal

Chapter 2 – Fundamentals of Laser Tattoo Removal v1.0
In fact, Mike demonstrated that such a sound can be generated when firing a laser on skin with no tattoo ink (see video). The sound is created when a very high fluence interacts with the skin, regardless of its colour, or ink content. It has NOTHING to do with the photo-mechanical process in the inks.
The spot diameter is very important in laser tattoo removal. Computer modelling of light travelling through the dermis indicates that larger spot diameters can transfer more energy to deeper parts of the skin, compared with smaller diameters.
So, it’s obvious that larger spot diameters should always be used in this application, assuming an appropriate fluence can be maintained. Some people seem to think that a smaller diameter will help to ‘focus’ the energy into deeper pigment – this is wrong!
In the real world, a laser operator can only choose the fluence and spot diameter since the wavelength(s) and pulsewidth are engineered into the laser. The only exception is with the Nd:YAG laser when the operator may choose between 1064nm and 532nm, using the frequency-doubling crystal.
Power & Power Density
Power is the rate at which energy is delivered. In other words, it is the energy used over time and is measured in watts (expressed as a capital ‘W’). One watt is one joule per second:
1watt = 1joule/1second
So, a light bulb rated at 60 watts will emit 60 joules of light energy every second. Likewise, a 1 kilowatt (or 1 kW) electric fire will emit 1000 watts of radiative energy every second – in this case the energy will be seen as light (usually orange/red in colour) and felt as heat (which is infra-red energy) - watch this interesting video.
Power is probably the most important laser/IPL parameter after wavelength. This is simply because it is the power which determines the tissue reaction. If the power is too high or too low then the desired reaction will most likely not occur.
A high energy beam of light delivered over a long time may result in too much thermal damage in tissue. But, the same high energy beam delivered in a very short time may induce the perfect response, as in tattoo removal.
Similarly, a low energy beam delivered over a long time period may stimulate a low level tissue response, as with LED systems and skin rejuvenation.
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Chapter 2 LEVEL A Laser Tattoo Removal
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