Module 7 : Laser- I
Lecture   : Line Broadening in Lasers
 

with
           $\displaystyle g(\nu_0) = \frac{2}{\pi\Delta\nu}$

  Exercise:
  Verify the normalization of the lineshape function.
   
2.5.3 Doppler Broadening:
 
We are familiar with Doppler effect in sound by which an observer perceives a change in the frequency emitted by a source when there is relative motion between the source and the observer. The apparent frequency is more than the source frequency when the source and the observer apprach each other and is less than the source frequency if they are receding from each other. Similar Doppler shift occurs in case of electromagnetic waves as well, excepting that unlike in the case of sound waves, the mediunm does not play any role.
When the observer and the source are stationary, the separation between two successive crests or troughs is $ \lambda_0$, where $ \lambda_0$is the wavelength emitted by the source. If $ c$is the velocity of light, the frequency $ \nu_0= c/\lambda_0$.
If the source is moving towards the observer with a speed $ v$, two effects have to be considered arising out of special theory of relativity.
   
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