Page 27 - LASERS & IPLS IN MEDICAL/AESTHETIC APPLICATIONS

Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.1
Basic Laser Design
Laser is an acronym for Light Amplification of Stimulated Emission of Radiation.
All solid-state lasers follow a basic design (apart from semi-conductors – see below).
At the heart of every laser is a medium. This may be a crystal, a gas or a liquid. This medium is the stuff that is ‘excited’ and it determines the laser output parameters. The collection of medium, a pumping energy source and 100% and partial mirrors are known as the ‘laser cavity’.
Figure 8: The basic layout of a solid-state laser
The pumping energy source is the ‘driver’ of the laser. The atoms in the medium must be ‘excited’ – this means that the electrons in the outer shells of those atoms absorb energy from the pumping source and ‘jump’ into higher orbits.
However, the electrons cannot stay on those higher energy orbits for long – quantum physics doesn’t “like” it! When those electrons fall back into their natural orbits the energy they gained from the pump source is released as photons of light. This is known as ‘spontaneous’ emission. (See picture below). Click here to see a good video on how lasers work...
Figure 9: Laser rods – each rod will generate a different wavelength
These spontaneous photons fly around in all directions. But some of them will move in the same direction as the axis of the medium and strike the mirrors. The ‘rear’ mirror is a ‘total reflector’ – it will reflect 100% of the photons striking it.
Those photons will fly back through the medium and interact with other atoms, stimulating their electrons. When those electrons fall back into their orbits, they will also release photons – these ones are ‘stimulated’ since they were excited by the spontaneous photons. This is where the term ‘stimulated emission of radiation’ comes from! At this point, the medium is ‘lasing’.
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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