Types of Lasers

The laser diode is a light emitting diode that uses an optical cavity to amplify the light emitted from the energy band gap that exists in semiconductors. (See Figure 6.) They can be tuned to different wavelengths by varying the applied current, temperature or magnetic field.

Figure 6. Semiconductor laser diagram


Gas lasers consist of a gas filled tube placed in the laser cavity as shown in Figure 7. A voltage (the external pump source) is applied to the tube to excite the atoms in the gas to a population inversion. The light emitted from this type of laser is normally continuous wave (CW). One should note that if brewster angle windows are attached to the gas discharge tube, some laser radiation may be reflected out the side of the laser cavity. Large gas lasers known as gas dynamic lasers use a combustion chamber and supersonic nozzle for population inversion.



gas laser diagram



Figure 7. Gas laser diagram

Dye lasers employ an active material in a liquid suspension. The dye cell contains the lasing medium. These lasers are popular because they may be tuned to several wavelengths by changing the chemical composition of the dye. Many of the commonly used dyes or liquid suspensions are toxic.

Free electron lasers such as in Figure 8 have the ability to generate wavelengths from the microwave to the X-ray region. They operate by having an electron beam in an optical cavity pass through a wiggler magnetic field. The change in direction exerted by the magnetic field on the electrons causes them to emit photons.


electron laser

Figure 8: Free electron lasers

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