ZaKi AbaaS
مؤسس المنتدى
عدد الرسائل : 91
العمر : 53
البلد : ismailia
العمل/الترفيه : التربية والتعليم
المزاج : رايق
تاريخ التسجيل : 18/11/2007
 |  موضوع: Chapter 14 : Laser  السبت يناير 12, 2008 2:43 am | |
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1- Spontaneous emission: It is the emission from one excited atom as it relaxes from a high energy level to a low energy level after its lifetime interval is over and under no external stimulus.
2- Stimulated emission:
It is the emission from one excited atom as a result of a collision with an external photon, which has the same energy as the one that caused it to be excited. Photons at the end come out in coherence, i.e. having the same phase, (direction and frequency)
3- Properties of laser beam:
a- spectral purity (monochromatic)
b- collimation (parallel rays)
c- Coherence (same phase and direction)
d- Concentration (high intensity and small diameter)
4- Laser Action: :
a- The active medium must be in the state of population inversion.
b- Emission of radiation of the excited atom through the stimulation emission.
c- Amplification of stimulated emission through the resonant cavity.
5- Basic elements of laser:
a- an active medium
b- a source of energy.
c- a resonant cavity.
6- He-Ne laser is a gas laser:
in which the active medium is a mixture of helium and neon in ratio 10: 1
7- Laser applications:
a- 3D photography (holography)
b- Medicine (e.g. treating retinal detachment) c- Communications.
d- Military application.
e- Industry.
f- CD recording.
g- Printing.
h- Arts and shows
i- Surveying
j- Space research |
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