Download 4-23

應用物理學系 0932365 張勝騏
Pedrotti OPTICS: Problem 4-23
Estimate the Doppler broadening of the 706.52-nm line of helium when the gas is at
1000K. Use the root-mean-square velocity of a gas molecule given by
3RT
M
where R is the gas constant, T the Kelvin temperature, and M the molecular weight.
 r m s
Ans:
 rms =
J  K/mole.K
3  8.314  1000
(
) = 2.497  10 3 (m/s)
kg/mole
0.004
'

= 1
c
，  '  (1 -
2.497  10 3
)  706.52 (nm) ，  ' = 706.514 (nm)
3  10 8
   ' -  = 0.006 (nm)
So the answer is
，because spectral width is 2 
2  = 0.012 (nm).
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