Page 150 - An Introduction to Laser Tattoo Removal
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Chapter 2 – Fundamentals of Laser Tattoo Removal v1.0
Appendix 7 - Absorption of laser energy by ink particle atoms
What determines the temperature rise on the surface of an ink particle? Well, it depends on a number of important things:
1. The incident wavelength
2. The absorption properties of the ink
3. The incident fluence
When a photon of light encounters an atom, there is a certain probability of that photon being absorbed. That probability depends on two factors:
a. The absorption cross-section of the atom for the incident wavelength, σabs
b. The total area of that atom presented to the incoming photon, A
The probability can be found by calculating the cross-sectional area divided by the total area:
Probability of absorption = σabs / A
The cross-sectional area, for any given ink atom, depends on the wavelength. This explains why some colours absorb some wavelengths better than others – the cross-sectional areas are simply larger!
Figure 73: The red photon encounters an atom with a relatively small absorption cross-section. Therefore, its probability of being absorbed by the atom is small. The green photon encounters the same atom, but this time the cross-sectional area is larger – simply because the photon is green! As a direct consequence, the probability of absorption is much greater.
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Chapter 2 LEVEL A Laser Tattoo Removal
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