We use a diode laser locked to a Rb transition as the frequency reference, along with a scanning Michelson interferometer, to make precise frequency measurements of atomic energy levels. The high precision is possible because the Rb reference frequency is known with submegahertz accuracy. We measured the frequencies of the D lines in K and obtained the following values: 12 985.169 60(20) cm-1 for the 4P1/2 state (D1 line), 13 042.875 95(21) cm-1 for the 4P3/2 state (D2 line), and 57.706 35(24) cm-1 for the 4P3/24P1/2 fine-structure interval. The errors represent approximately an order-of-magnitude improvement over tabulated values.

© 2004 Optical Society of America

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Figures (2)

Fig. 1
Fig. 1

Energy levels of  39K. The relevant energy levels of  39K in the ground 4S state and the first excited 4P state are shown. The various hyperfine levels are labeled with the values of the total angular momentum F, and the number on each level is the energy displacement (in megahertz) from the unperturbed state (from Ref. 11). The two insets at the left are saturated-absorption spectra on the D1 and D2 lines for transitions starting from the F=2 ground level.

Fig. 2
Fig. 2

Line shape of the saturated-absorption spectrum for F=2F transitions. Probe detuning is measured from the center of gravity of the line. The measured spectrum, shown as open circles, is a convolution of six peaks. The solid curve is a fit to the six peaks with the linewidth as a fit parameter. The best fit yields a linewidth of 22.3(7) MHz. The dotted curve is the expected line shape if the linewidth is the natural linewidth of 6.1 MHz. The peak of the spectrum is shifted from the center of gravity by +1.5 MHz for the solid curve and by +3.5 MHz for the dotted curve.

Tables (2)

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Table 1 Measured Wavelength Ratios and Energy Levels in Ka

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Table 2 Results of Second Set of Measurements of Wavelength Ratios and Energy Levels in Ka

Equations (3)

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4P1/212 985.169 60(13)(15)cm-1,
4P3/213 042.875 95(14)(15)cm-1,
4P3/2-4P1/257.706 35(19)(15)cm-1.