Page 74 - LASERS & IPLS IN MEDICAL/AESTHETIC APPLICATIONS

Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.1
Reflection
● When light encounters a surface it may undergo one of a number of events. One of these is reflection. In particular, it may undergo ‘specular’ or ‘diffuse’ reflection (see figure 39 below).
SPECULAR REFLECTIONS:
occur when the surface is relatively smooth (compared with the light’s wavelength). Light reflecting off a specular surface will ‘keep’ any information it possesses – such as spatial info like in an image. This is why mirrors are useful to observe the state of our hair in the morning...
DIFFUSE REFLECTIONS:
differ from specular reflections in that they occur at ‘rough’ surfaces such as the stratum corneum of the skin. This layer is composed of dead keratin cells stacked on each other in disarray, with no real pattern.
This creates an irregular surface, again, compared to the wavelength of the incident light. When light strikes such a surface the photons will reflect off in many different directions, losing any spatial information it may have possessed.
● Most natural objects will reflect light diffusely – only polished or ‘shiny’ objects generate specular reflections
Figure 39: Specular vs Diffuse reflections
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
Specular reflection – from a smooth surface like a mirror
Diffuse reflection – from rough surfaces like skin
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