Page 147 - An Introduction to Laser Tattoo Removal

Using the equation:
Optical Density = log10 (EDi / MPE)
Chapter 2 – Fundamentals of Laser Tattoo Removal v1.0
Calculating the minimum Optical Density for a QS/picosecond laser
To calculate the minimum optical density required for a Q-switched or picosecond laser, we must carry out the following calculations:
where EDi is the maximum incident energy density on the eye’s surface
and the MPE is the Maximum Permissible Exposure of the eye to that wavelength, which we can find in the chart below (this chart comes from the BS EN207:2017 Laser Eye Safety Standard)):
Figure 71: MPE (Energy Densities) curves for the wavelength range 400 nm to 10 microns
So, let’s imagine a Q-switched or a picosecond laser can output 12.5 J/cm2, what is the minimum OD we need to protect our eyes?
12.5 J/cm2
5 x 10-6 J/cm2
3 x 10-6 J/cm2 ________________________________________________________________________ 147
Maximum ED
MPE for a 5 ns (5x10-9 s) pulse at 1064nm
Chapter 2 LEVEL A Laser Tattoo Removal
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Or, for a 500 ps (0.5x10-9 s) pulse at 1064nm