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A Importance of optical period in coherent radiation

  1. Nov 23, 2016 #1
    I am reading a text on coherent radiation and not quite understanding a particular statement. To provide some background, the authors state that coherent radiation can arise from light-matter interactions even when considering lengths, ##L##, much smaller than the wavelength (i.e. ##V \sim L^3 << \lambda^3##) due to phase coherence in the medium if it satisfies certain conditions (e.g. initial population inversion, dephasing effects are negligible on the time-scale, ##T_P##, of the coherent bursts of radiation). Now the author states the following about the regime where ##T_P < \frac{\lambda}{c}##:

    "This regime is not physical: in order to observe it, one would have to realize the inversion of the medium in a time shorter than the optical period."

    It may be quite obvious what the author is saying, but why exactly cannot the burst occur on a timescale quicker than the optical period? If an ensemble of atoms, with ##L < \lambda## can coherently radiate, why can't atoms radiate on timescales of less than ##\frac {\lambda}{c}##? As long as they are sufficiently close and the interactions causal (i.e. ##T_P > \frac{L}{c}##), why can't coherent radiation occur? Perhaps at such high densities, dipole-dipole interactions may disrupt the process, but I don't quite understand the significance of ##T_P## being larger than the optical period. Any thoughts?
     
  2. jcsd
  3. Nov 29, 2016 #2
    Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.
     
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