Laser Light Amplification by Stimulated Emission of Radiation

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???????(Laser) Light Amplification by
Stimulated Emission of Radiation
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???????????????????????????

• 1. ?????????????? ?????????????????????????
• 2. ??????????????????????????????????????????
• 3. ??????????????????????? ???????????????????
  ????????? ??? ? ???????????????????
• 4. ???????????????????????

3
????????????? ??????????
4
???????????????????????????????????????? f
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???????????????? (Emission)
?????????????????????????? (Spontaneous
Emission) ????????????????????????????????????????
???????????????????????????????????????????????
E2 -E1 ??????????????????????????????????????????
???????
E2
E1
Spontaneous Emission
??????????????????????????????????? (Stimulated
Emission) ?????????????????????????????
??????????????????????????????? E2 -E1
?????????????????????? ??????????????????????????
??????????????????????????????? E2 -E1
?????????????????????????????????
???????????????????? ??????
E2
E1
Stimulated Emission
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????????????????
Excited medium
If a medium has many excited molecules, one
photon can become many. Stimulated emission leads
to a chain reaction and laser emission.
This is the essence of the laser. The factor by
which an input beam is amplified by a medium is
called the gain and is represented by G.
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??????????????
1. ?????????????? ???? , ?????(dye)
????????????,..
????? metastable state
2. ????????????????? ??????? , ?????? ,
?????????, ..

• 3. ?????????? --gt ???????????????????? 100
  ??????????????? lt100

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?????????????? (Laser medium)
excited state
1. ???????????????????????? 2 ????????????
?????????????????????????? (population inversion)
?????? ????????????????
Pump
LasingTransition
ground state
Two-level Laser
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2. ???????????????????????? 3 ????????????
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3. ???????????????????????? 4 ????????????
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Lasers