Lasers | 農藥百科
![Lasers](https://i.imgur.com/WMTbIbA.jpg)
由DWBall著作·2006·被引用119次—Whenapopulationinversionexists,anupper-statesystemwilleventuallygiveoffaphotonoftheproperwavelengthanddroptothegroundstate.Thisphoton, ...
![Lasers](https://i.imgur.com/WMTbIbA.jpg)
Under normal circumstances, the higher an energy level is, the less it is populated by thermal energy. Under some circumstances (for example, the presence of an upper energy level that has a relatively long lifetime), a system can be constructed so that there are more atoms/molecules in an upper energy level than is allowed under conditions of normal thermodynamic equilibrium. Such an arrangement is called a population inversion.
When a population inversion exists, an upper-state system will eventually give off a photon of the proper wavelength and drop to the ground state. This photon, however, can stimulate the production of other photons of exactly the same wavelength because of stimulated emission[1] of radiation. Thus, many photons of the same wavelength (and phase, and other similar characteristics) can be generated in a short time. This is light amplific...