Four-Wave Mixing Data

We began pumping 6852.5 angstrom light into the sodium vapor. Two photons of this energy excited the atoms to a virtual state just above the 3d state.  Then, we slowly lowered the energy to approach the resonant 3d line. As the incident energy approaches the energy of the 3d lines, the emissions from levels just above the 3p lines are suppressed. It seems that as we approach resonance, the phase matching condition is less easily met.   We also see a slight suppression in the main peaks as we move closer to resonance with thh 3d state.  Scanning the incident wavelengths from 6852.5 to 6855 angstroms, we found the main emission peaks shifted by about 0.4 angstroms.

Here you can see this higher emission level.

When the incident photon energy is decreased to match the 3d level, the line starts to be suppressed.

More suppression of the line...phase matching condition can't be met.

Due to the phase matching requirement, the light from the sodium vapor will be in a cone shape.  Here are two actual photos of the emission:

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