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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
When light encounters an atom or a molecule it can interact in a number of ways:
 This can be thought of as a photon of light ‘bouncing’ back off an object it interacts with. Without reflection it would be difficult to see anything!
Refraction occurs when a beam of light changes from one medium (air) into another medium (water). This usually means that the wavelength changes too – usually to a shorter length. We can observe refraction by looking through a bottle of water – the objects behind the bottle appear to ‘bend’ slightly, from their true direction. This is principally due to refraction of the light through the water.
When light encounters an object, it may be reflected from its surface or enter the object. Occasionally, it will encounter an ‘edge’. At such a location, diffraction may occur – this is the ‘dispersal’ or ‘spreading’ of the light beam from that edge.
  Absorption occurs when the energy within photons of light are transformed into another form of energy within some medium. This may be heat or vibration (which can be perceived as sound). In medical/aesthetic treatments, absorption is critical since it determines the outcome of the treatments. (See video.)
When light interacts with atoms or molecules, it invariably scatters. This typically involves absorption of the photons followed by the generation of new photons. These ‘new’ photons will usually move in a different direction to the original photons. This change of direction is what physicists call ‘scattering’. (See video.)
  Refraction – how it changes wavelengths in the skin
● When light enters the skin it ‘slows down’. This is due to the change in refractive index (the refractive index of air is about 1.0, whereas the skin is in the range 1.33 to 1.55).
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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