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Research Program

The main objective of our research on the NIST IR-vis-UV Fourier transform spectrometer is the observation and analysis of complex atomic spectra. In particular we are interested in the neutral, singly-ionized and doubly-ionized rare earth and transition group elements, where the spectra may consist of many thousands of lines from hundreds of energy levels. The high resolution of the Fourier transform spectrometer is needed to identify these lines correctly and to assist in locating new energy levels. The linear intensity response of the spectrometer is also needed to be able to measure line intensity ratios correctly, and thus deduce branching ratios and transition probabilities.

One of our principal research programs involves observation and analysis of the spectra of neutral and singly-ionized dysprosium and holmium, which are elements of interest for the lighting industry. These elements are commonly used in new high-intensity lighting designs, and accurate atomic data are needed to model the discharge and predict the probable effect of changes in the design. We are using high-current hollow cathode lamps to excite the spectra. These lamps combine good excitation with narrow line widths, and are excellent sources for use with a Fourier transform spectrometer as they are very stable sources.

Another important program involves the observation of spectra of interest to astrophysics, in particular for the study of chemically-peculiar stars. In addition to the high-current hollow cathode lamps, we also use a Penning discharge source. This provides higher excitation than hollow cathode lamps, and can generate spectra of doubly-ionized and in some cases, triply-ionized spectra. The elements of particular interest here are the iron-group elements which have many thousands of lines that dominate solar and stellar spectra. Some of this research is done in collaboration with research groups at Imperial College, London, UK and at Lund University in Sweden.