Page 140 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Case 2 – However, in some cases, the photons entering the skin will be scattered and its path will be turned so much that they leave the skin altogether. These are known as back-scattered photons. Once they leave the skin they are back in the environment and a number of things might happen.
They may strike your clothing and be absorbed by atoms there. They might even strike your skin and raise the temperature there a little – usually this is not noticeable.
Or, a ‘rogue’ photon might escape the room through a window and be released into the atmosphere. Up there it will encounter many gaseous atoms, or water vapour, and be scattered all over the place. It is entirely possible that such a photon might be scattered enough times that it ends up just outside Sao Paolo and fly up a dog’s left nostril, only to finally absorbed there! Who knows? That dog might be called Raul...
This photon might have existed for around 1 to 10 seconds. Possibly longer depending on how many scatterings it encountered.
Case 3 – Another possibility is that a photon escapes from the Earth’s atmosphere and is released into space. This is not very likely but it is still possible.
The above image was kindly supplied by https://drawception.com/game/ydSQ9T4APY/alien- sandwich/
Such a photon might then travel through space for millions of years, quite happily minding its own business. Eventually, it may encounter a strong gravitational field, say from a star, and be redirected towards a spacecraft, which just happens to be passing by. Possibly, it might enter the spacecraft through a window and be reflected of its shiny interior until finally striking a ‘sprongeeiej’ sandwich (delicious!!), which is in the process of being eaten by an alien called Bob!!
This photon, from Earth, will raise the temperature of the sprongeeiej sandwich, slightly. Of course, this might occur millions of years in the future, so none of us will notice...
You might think that this is highly unlikely. But you should remember that every time you fire a shot of laser or IPL energy you are generating a huge number of photons. So, even though the probability of any individual photon going on a space trip is very small, it is not zero!
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