Page 272 - Blog Posts v1

travel, many photons can easily be heading in the ‘wrong direction’ back towards the skin’s surface. They will be lost as ‘back-scattered’ light, if they leave the skin.
• My friend, PA Torstensson, did some Monte Carlo calculations on this and found that up to half of all photons of the 1064 nm persuasion might be lost from back- scattering!! See my paper on this.
• This is remarkable, especially when considering laser treatments of the skin. We might be losing half of our energy simply due to scattering.
• Another important issue is that, as you saw above, scattering causes the photons to ‘spread out’ as they penetrate into the skin. This means that the spot diameter increases with depth.
• This is not good!! If we have set our laser to generate a certain fluence at the skin surface, say 5 J/cm2, then, at some depth in the skin it will fall to 4 J/cm2, then 3 J/cm2, then 2 J/cm2 and then 1 J/cm2. What is fluence?
• Now, if the target we want to destroy (blood vessel, hair follicle) requires a minimum of, say 3 J/cm2, then, simply because of scattering, the treatment will stop at some depth. Below this depth, the fluence will be too low to effect the changes we
want click here.
• So, it is important to consider the depth of your target when setting your fluence at the skin surface.
• Back to our little, red photon. So, we have encountered many wonderful atoms and molecules and exchanged many energies with them on our trip so far. However, it is important to know that the photon we are currently sitting on has absolutely no
Mike’s Blog Posts 272