Reference lines in the optogalvanic spectra of uranium and thorium over the wavelength range 694–755 nm

The optogalvanic spectra of uranium and thorium are convenient sources of lines with which to calibrate wavemeters for high-resolution laser spectroscopy. We used hollow-cathode lamps for both uranium and thorium to observe the spectra, using a single-frequency cw dye laser operating over the wavelength range 694–755 nm. Eight uranium and seven thorium lines were measured with an accuracy of a few parts in10

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 with our Fabry–Perot wavemeter. The estimated uncertainty of the measurements is 0.0002 cm-1 for both species. The results were compared with several previous measurements of these lines and were found to be in good agreement with values determined by Fourier-transform spectroscopy.