Page 30 - LASERS & IPLS IN MEDICAL/AESTHETIC APPLICATIONS

Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.1
Technical point...
In reality, no laser can truly emit a ‘single’ wavelength – that goes against the laws of physics – Heisenberg’s Uncertainty Principle, to be precise. In truth, there is a very small range of wavelengths around a ‘fundamental’. This might be a few nanometres, or less than 1 nm, in some cases. So, a laser wavelength quoted as 1064nm is, in reality, in the range 1062 – 1066nm (approximately, depending on the laser design).
Divergence (or Directionality)
● Most lasers can be viewed as a “point source”. This means that their light emanates from a ‘point’ rather than an ‘extended source’ (like a light bulb). The emerging beam is usually very narrow and does not spread out much over distance (apart from some diode lasers). This is a measure of its divergence. Ordinary light sources diverge all over the place – their light fires out in all directions simultaneously.
● Lasers are unique in that their light diverges very slightly over distance. However, in reality, it does diverge – the beam size expands the further you move from the laser source. If you fire a laser beam at the moon the beam diameter will have expanded to around 6,500 metres by the time it reaches the moon’s surface (around 385,000 km from the Earth’s surface – more info here).
● However, at the distances we use here on Earth, the divergence is usually very small. It is this small divergence that allows us to direct all of the energy to a small area on tissues.
Figure 11: Due to divergence a laser beam diameter increases with distance from the laser’s aperture
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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