Page 88 - An Introduction to Laser Tattoo Removal

Chapter 2 – Fundamentals of Laser Tattoo Removal v1.0
Power Density
1 cm
IPLs
Over 2.5 km
Around 100 – 5000 cm
Typical lasers
QS lasers
Figure 42: Comparison of Power Densities between IPLs, lasers and QS lasers (when ‘heights’ are used to represent power densities)
The power density of the IPL system is calculated by dividing 20 J/cm2 by 10 ms yielding 2,000 W/cm2. However, the laser’s power density is 5 J/cm2 divided by 10 ns. A nanosecond is 1 billionth of a second so the peak power density of this laser will be 500,000,000 W/cm2 in each pulse.
So, you can see that this laser can produce a power density which is 250,000 times that of the IPL system! If you were to draw a graph and show the maximum power density of the IPL as a 1 cm high point, then the laser would need a point 2.5 km high on the same graph (see figure 41 above)!! Picosecond lasers are even higher!
Given that we now know that power density determines the outcome of any treatment you can see how knowing the fluence is not enough – you MUST know the power density.
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Chapter 2 LEVEL A Laser Tattoo Removal
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