Absorption and Emission Spectra: Ground State Hyperfine Structure

The first graph that was generated was an absorption spectrum produced by the probe beam. This spectrum did not include the excited state hyperfine peaks because the pump beam was not going through the cell. The peaks in this spectrum represent the following transitions.

The transition represented by the red line for ⁸⁷Rb corresponds to the first peak in the spectrum (going from left to right) at approximately -14,250 MHz. The transition represented by the orange line for ⁸⁷Rb corresponds to the last peak in the spectrum at approximately -6000 MHz. The transition represented by the green line for ⁸⁵Rb corresponds to the second large peak in the spectrum at approximately -12,900 MHz. The transition represented by the blue line for ⁸⁵Rb corresponds to the third peak in the spectrum at approximately -9000 MHz. The spectrum is shown below. ¹

There seems to be a smaller peak apparent to the left of the second absorption peak. This peak results from the excited state hyperfine structure. The first main peak, peak 1, is showing some hyperfine structure. The separation between the two levels in the excited state hyperfine structure is great enough so we can see that there is more than one peak, or one transition happening. We will not be able to see all of the excited state hyperfine structure peaks until we use both the probe beam and the pump beam, however.

Looking at the graph, the frequency difference between the levels in the ground state hyperfine structure for ⁸⁷Rb is 8750 MHz. This compares to a reported value of 6834.6 MHz for the frequency difference between the levels in the ground state hyperfine structure for ⁸⁷Rb. The frequency difference between the levels in the ground state hyperfine structure for ⁸⁵Rb is 3900 MHz. This value compares to a reported value of 3035.7 MHz for the frequency difference between the levels in the ground state hyperfine structure for ⁸⁵Rb.

The emission spectrum peaks (shown below) correspond to these same transitions except the electron is returning to a lower energy state, emitting a photon. Here too there are signs of the excited state hyperfine structure in the second and fourth peaks.

There are four distinguishable peaks in the emission spectrum just as there are in the absorption spectrum. These four peaks fall at approximately the same frequencies as to the absorption peaks. This indicates that much of the time the electrons are emitting photons of the same frequency as they absorbed to jump to higher energy levels.

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