Page 44 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
 Interesting...
When you go out on a sunny day you can feel the heat from the sun. What you are actually feeling is due to the sun’s infra-red photons being absorbed by your water molecules in the dermis.
However, you can’t ‘feel’ ultraviolet light – there’s very little sensation when those photons are absorbed. Yet, it is the UV photons which stimulate the tanning process in your skin – not the IR. Clouds will absorb much of the IR from the sun, while UV light just passes straight through them. Hence, you can get a suntan, even on a ‘cold’, sunless day!!
Frequency of Light
● The frequency is directly related to the wavelength through the speed of the light. However, the speed of light depends on which medium it is passing through.
● In outer space (which is essentially a vacuum), the speed of light is at its maximum – approx. 300,000 km/second (which is around 186,000 miles per second). In space the refractive index is 1.0.
● When light enters another medium, like water, the refractive index will be higher (there is no refractive index less than 1.0!) Refractive index can be thought of as the ‘optical density’ of a medium – the higher the index, the more optically dense it is, the slower light travels through it.
Figure 23: Light interacts with matter in various ways
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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