Coherent Transient Study of Velocity-Changing Collisions

  • J. Schmidt
  • Paul R. Berman
  • Richard G. Brewer


The effect of velocity-changing collisions on the optical phase memory of coherently prepared molecular gas samples is examined by the method of Stark-pulse switching. Experiments are interpreted through the solution of a transport equation, which extends the earlier Fokker-P1anck description known both in NMR and in Dicke line narrowing. The magnitude of a characteristic velocity jump for binary molecular collisions and its cross section are thereby obtained.

It is well known that collisions between molecules can influence their optical lineshape through changes in molecular velocity. Theoretical discussions 1 – 5 of this problem usually invoke a Brownian motion diffusion model in velocity space that is based on a solution of the Fokker-Planck equation.6,7 A Doppler or Gaussian lineshape is predicted for low pressure and a Lorentzian profile for high pressure, the width becoming narrower with increasing presure as first recognized by Dicke.1 To be valid, these treatments imply characteristically small Doppler phase changes ktΔurms ≪ 1 over the period of observation t where \( \mathop {\rm{k}}\limits^ \to \) is the propagation vector of light and Δurms is a characteristic velocity jump, essentially the root mean square change in velocity per collision.


Spin Echo Density Matrix Element Velocity Jump Collision Kernel Photon Echo 
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Copyright information

© Plenum Press, New York 1974

Authors and Affiliations

  • J. Schmidt
    • 1
  • Paul R. Berman
    • 2
  • Richard G. Brewer
    • 1
  1. 1.IBM Research LaboratorySan JoseUSA
  2. 2.Physics DepartmentNew York UniversityNew YorkUSA

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