There was some question in class today about what happens when the
photon has an anergy above vs. below the atomic resonance in the
context of scattering. Think of it like the slinky demo I did at the
start of the semester: if you oscillate the slinky too slowly, it
doesn't respond much and you dont get very much energy transfer to the
slinky. If you oscillate it too fast, it just shakes and never
receives much energy from your hand. If you shake it just right, it
transfers lots of energy and you get a resonance effect. Same thing
for these atoms: the electron acts like a spring and the scattering
effect goes way up near the resonance frequency. Away from the
resonant frequency on either side the electron doesn't respond as
much, and you dont get much scattering. This also can be used to
understand the effect of dispersion. Scott will talk about that on
Friday and I can review it with you briefly on Monday.