Page 154 - Sensors and Control Systems in Manufacturing

Classification and Types of Sensors

FIGURE 2.108 Spectrum of standard white light. 115

active medium. For example, the ruby laser has a crystal of ruby as its
active medium while the CO laser has carbon dioxide gas.
2
The wavelength emitted by a laser is a function of the active
medium. This is because the atoms within the active medium have
their own characteristic energy levels at which they release photons.
It will be shown later that only certain energy levels within the atom
can be used to enhance stimulated emission. Therefore, a given active
medium can produce a limited number of laser wavelengths, and
two different active media cannot produce the same wavelengths.
Table 2.10 contains a list of materials commonly used in lasers and the
corresponding wavelengths that these materials produce.
The active medium is the substance that actually lases. In the
helium-neon laser, only the helium lases.

2.12.2.2 Excitation Mechanism
The excitation mechanism is the device used to put energy into the
active medium. Three primary types of excitation mechanisms exist—
optical, electrical, and chemical. All three provide the energy neces-
sary to raise the energy state of the atom, ion, or molecule of the active