12 FI G. 14: The dependence of the center-of-gravity frequencies fo r the 6S 1 / 2 → 6P 3 / 2 → 7D 5 / 2 transition on the power (upper lef t)  the magnetic field (upper right)  and the Cs vapor pres- su re (bottom). The straight line in the power dependence pl ot is a linear weighted fit to the data. The vertical axis has be en offset and centered so that the nominal operating point is at zero. The power is plotted as a function of the fraction of the maximum power. The magnetic field is plotted as a fu nction of the residual magnetic field. FIG. 13: The experimental spectrum (upper trace)  fit to the 6S 1 / 2 → 6P 3 / 2 → 7D 5 / 2 transition (middle trace)  and of the calculated contribution from the 6S 1 / 2 → 6P 3 / 2 → 7D 3 / 2 transition (lower trace). Note that the vertical scales are different for the two figures. -0.1 0.0 0.1 1.0 0.5 0.0 Normalized Power Center-of-Gravity Frequency Shift [MHz] -0.2 0.0 0.2 2 1 0 Normalized Magnetic Field Center-of-Gravity Frequency Shift [MHz] -0.1 0.0 0.1 8 6 4 2 0 Pressure [mPa] Center-of-Gravity Frequency Shift [MHz] 0.7740 0.7738 0.7736 f$_{rep}$ - 1000 MHz [MHz] 0.7728 0.7726 0.7724 f$_{rep}$ - 1000 MHz [MHz] Experiment 7 D$_{5/2}$ Fit 7 D$_{3/2}$ Calculation Experiment 7 D$_{5/2}$ Fit 7 D$_{3/2}$ Calculation 7 2 P$^{✑}$ 6  2 S 1/2 Fluorescence from  6  2 S 1/2 ✒ 6  2 P 3/2  ✓ 7  2 D 3/2  5/2 Excitation 7  2 P$^{✔}$ 6  2 S 1/2 Fluorescence from  6  2 S 1/2 ✕ 6  2 P 3/2  ✖ 7  2 D 3/2 5/2 Excitation 0 1 2 0 2 4 1 3 5 Group 1 Group 2 Group 3 Group 4 Group 5 35 kHz in the optical frequency. There is no evidence for a dependence of the extracted hyperfine A constant  and w e find a magnetic-field uncertainty of 6 kHz for it. For th e B constant we find an uncertainty of 125 kHz. We see no clear evidence for any temperature depen- dent effects. Using the larger of standard deviation or the uncertainty in the mean  we find uncertainties of 7 kHz  1 kHz  and 38 kHz for the temperature-dependent uncer- tainties of the center-of-gravity frequency  the hyperfine A constant  and the hyperfine B constant  respectively Applying these uncertainties we find We have used the technique of velocity-selective two- photon excitation to measure the center-of-gravity fre- quencies and the hyperfine coupling constants for the 8S$_{1}$$_{/}$$_{2}$   9S$_{1}$$_{/}$$_{2}$   7D$_{3}$$_{/}$$_{2}$   and 7D$_{5}$$_{/}$$_{2}$ states of Cs. The results for all of the transitions are summarized and compared to other published experimental values in Table II. This technique has potential metrological applications for sec- ondary frequency standards at optical wavelengths. At a more fundamental level  the hyperfine coupling measure- ments are valuable in improving atomic structure calcu- lations. The measurement accuracy of multiple transi- tions at significantly different wavelengths rivals that of transition. For the first stage the intensity over the 10 nm bandwidth was varied from ≈ 22 W/cm 2 to ≈ 5 W/cm $^{2}$. Data were taken at cell temperatures corresponding to saturated vapor pressures of 0.15  1.05  3.9  and 8.5 mPa. The dependence of the center-of-gravity on the varied parameters is shown in Fig. 14 and are summarized in Table I. As with the previous transitions there was no signifi- cant shift arising from the light power. A linear fit gave a slope of − 23(62) kHz /P   where P is the normalized operating power. This gives us an uncertainty of 85 kHz in the center-of-gravity frequency. We found uncertain- ties in the hyperfine A and B constants of 11 kHz and 458 kHz  respectively. Unlike the other transitions studied here  we did ob- serve a dependence of the center-of-gravity on the mag- netic field (Fig. 14). There was clear evidence of broad- ening in the peaks at the largest magnetic fields. We attribute the shift to a break down of the line-shape model as the line broadens coupled with the overlap of the peaks. In this case  we base our estimate of the uncer- tainty on the difference of the point taken at the zeroed field with the residual field and find an uncertainty of V. CONCLUSIONS ν$_{6S}$$_{1}$$_{/}$$_{2}$$_{:7D}$$_{5}$$_{/}$$_{2}$ = 781 522 153 . 68(16) MHz A$_{7D}$$_{5}$$_{/}$$_{2}$ = − 1 . 717(15) MHz B$_{7D}$$_{5}$$_{/}$$_{2}$ = − 0 . 18(52) MHz .