Page 28 - 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 above process continues for a time generating many, many stimulated photons. Some of them can escape from the laser cavity since the output coupler mirror (4) is a “partial” reflector. This mirror reflects anywhere between 90 and 99% of the photons back into the cavity thereby releasing a small percentage into the outside world.
The photons will escape from the cavity make up the laser beam. As you can see, most of the laser energy remains ‘trapped’ within the cavity, never being released into the world. They will eventually be absorbed by electrons within the medium and generate thermal energy (heat) instead of light. This is part of the reason why many lasers need to be cooled during operation.
Spontaneous Emission
 An electron absorbs some energy from the pumping source and jumps into a higher orbit.
After a very short time, it falls back into its natural orbit, releasing a photon with the same energy it had absorbed.
This energy determines the photon’s wavelength, via the Planck equation (see the LEVEL C section for more detail on this).
 Only a relatively small number of materials can be made to ‘lase’ – that is, generate stimulated photon emissions. Most materials can never lase and so cannot be used to create laser beams.
 Laser wavelengths
Ultraviolet Visible
Mid infrared
      Near infrared
Wavelength (nm)
Figure 10: Some common laser wavelengths
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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