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Summary

 

Here we gather summarize the main results of what follows in this section.

To determine the scattering properties of a particular potential, one first divides space into three regions as in Figure 7. The potential is taken to be constant in the ``source'' region s, extending by convention from tex2html_wrap_inline1621 to x=0. This is the region from which particles from an external source come to interact with the potential. It is also this region into which particles reflect back. The potential is also be taken constant in the ``transmitted'' region t, extending by convention from x=L to tex2html_wrap_inline1629 . This is the region into which particles originating from the source in Region s may be transmitted. Finally, in Region c, where the collisions generating the scattering takes place, the wave functions may take on arbitrarily complicated forms. Note that one may generalize our results to situations where the particles are incident onto the potential from the right by changing the direction the x-axis.

Once the potential is determined, the first step in analyzing the problem is to solve the TISE with left-incident boundary conditions, which state that the form of the wave function in Region t is just some pure beam state tex2html_wrap_inline1637 of particles traveling to the right. This determines the entire solution to the TISE, which, by multiplying through by a normalization constant, may always be put into the following general form,

equation251

where tex2html_wrap_inline1645 is the wave vector in Region t written as a function of the incoming wave vector in Region s. Once the quantum amplitudes r(k) and t(k) for the reflected and transmitted beams, respectively, are determined, all of the relevant issues in scattering may be studied.

Probability of Reflection and Transmission- The magnitudes of the scattering amplitudes give the probabilities of a particle reflecting or transmitting,

eqnarray267

respectively, where tex2html_wrap_inline1583 is the wave vector about which the incoming wave packet is centered.

Time delays- The time delays for transmission and reflection after the source packet collides with Region c are determined by the phases of the quantum amplitudes, which are defined through

eqnarray270

The reflected packet emerges into Region s a time tex2html_wrap_inline1661 after the source packet collides with Region c, and the transmitted packet emerges into Region t a time tex2html_wrap_inline1667 after the source packet collides with Region c,

  eqnarray274

Here, tex2html_wrap_inline1583 is the wave vector about which the incoming wave packet is centered and tex2html_wrap_inline1673 is the classical velocity expected of a particle propagating in Region s.


next up previous contents
Next: Solutions of the TISE Up: General Features of Scattering Previous: General Features of Scattering

Prof. Tomas Alberto Arias
Thu May 29 15:19:37 EDT 1997