|There is often a need for reproducible, high-accuracy wave number standards not only for classical spectroscopic techniques but for laser based techniques as well. The optogalvanic spectra of uranium and thorium using commercial hollow cathode lamps have proven to be very useful standards over a broad range of wavelengths. These lamps are particularly useful in the near IR where the I2 standard becomes difficult to use.
The optogalvanic spectra is easily observed: a weak laser beam (less than 10 mW) is chopped and directed co-axially into the cathode of the lamp. Changes in the lamp current that occur when a resonance is achieved are detected by a drop in voltage across the lamp's ballast resistor with a lock-in amplifier. With have measured 23 thorium and 24 uranium lines with our Fabry-Perot wavemeter from 13 250 cm-1 to 17 450 cm-1 to a precision of better than 0.0004 cm-1.
For more details, please see the report on this work:
C.J. Sansonetti and K.-H., Weber, J. Opt. Soc. Am. B 1, 361 (1984).
W. DeGraffenreid and C.J. Sansonetti, J. Opt. Soc. Am. B, 19, 1711 (2002).