Page 73 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
● The light we see coming from any object is the light which is not absorbed by that object. This is why it is difficult to determine colours at night – many street lights use sodium, which is why they appear yellow. But when this yellow light bounces off red or blue or green cars, they don’t exhibit their ‘normal’ colours.
● That’s because we are seeing only yellow light being reflected off the car’s pigments – there is no ‘subtraction’ process as with white light. Click for a video of this process.
Figure 38: Why is a blue object, blue?
● We can exploit absorption in medical/aesthetic treatments with light. Using special equipment, it is possible to determine the wavelengths which are more strongly absorbed by targets such as blood, hair, melanin etc.
● These are known as ‘chromophores’ (see next section). If we know the strongly absorbed wavelengths for any particular chromophore, we can choose a laser with that wavelength, knowing that a lot of its energy will be preferentially absorbed by that chromophore.
    This is the basis of a very important mechanism in medical/aesthetic laser treatments –
Selective Photothermolysis
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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