A very simplified version of laser mechanics; the laser produces a beam of light energy that is coherent, monochromatic and collimated. That means the light is all the same wavelength, the waves are in phase and it is focused into a fine beam.
The various lasers used in dentistry are usually identified by the active medium material such as Yag, Diode, Erbium,Chromium:Yttrium, CO2 or Alexandrite. This material is what determines the wavelength of the laser.
Different wavelengths of light energy are absorbed by different substances. For example some wavelengths are absorbed by water and some wavelengths pass right through water. If a substance absorbs the laser energy it will immediately take on the energy of the laser, usually as heat. The rapid heating of the tissue is what causes the changes we see with a laser.
Each wavelength will affect the tissues in quite different ways. For example a diode laser is absorbed by dark colors such as hemoglobin. That makes it ideal for cutting soft tissue but it will have no effect on tooth structure. On the other hand the energy produced by the YSGG (Biolase) is partially absorbed by water and can be used to remove tooth structure.
According to Dr. Clara Munera the High Tech Marketing Manager for Ivoclar the reason the diode is so gentle is that the energy is directed to the tissue practically on the cell level. There is very little inflammation, edema or cell damage. By comparison electrosurge energy is dispersed into adjacent tissues and results in much more trauma and post operative inflammation.
Lasers have many advantages over conventional modalities. Lasers will seal blood vessels, lymphatic vessels and nerve fibers. As a result there is less swelling, less scarring, little need for sutures, and post operative pain is decreased by 90%.