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J. E. Lawler, F. L. Roesler (Univ. of Wisconsin, Madison WI 53706), J. Harlander (St. Cloud State Univ., St. Cloud, MN 56301)
All reflection Spatial Heterodyne Spectrometer (SHS) designs have the potential to revolutionize spectroscopy in the VUV. The advantages of interferometric spectrometers such as the Kitt Peak 1m Fourier Transform Spectrometer (FTS) in the near UV, visible, and IR for laboratory measurements of spectroscopic data including emission branching fractions, improved level energies, and hyperfine/isotopic parameters are well documented. These advantages include: (1) very high spectral resolving powers, (2) excellent absolute wavenumber accuracy, (3) extremely broad spectral coverage, (4) high data collection rates, and (5) insensitivity to source drift during branching fraction measurements. Some progress has been made in extending spectroscopic interferometry into the VUV using modified versions of Chelsea Instruments FTS, but beam splitter performance issues and the problem of generally low sensitivity at wavenumbers above 67,000 cm-1 have proven to be quite stubborn. We are starting the construction of a SHS which has promise of extending spectroscopic interferometry to the window limit (~90,000 cm-1) and eventually above the window limit. In addition to the lack of transmitting optics, the SHS has other advantages. Optical imperfections are much more serious in a traditional Michelson FTS than in a SHS. The localized fringes of equal thickness in a SHS deviate from straight lines due to optical imperfections, but such deviations can be corrected with software after transferring the interferogram from the CCD. Similar optical imperfections from either figure or index of refraction variations in a Michelson FTS lower fringe contrast and degrade the instrument sensitivity. The use of a CCD detector array to record the spatially distributed interferogram means that the SHS is quite compatible with transient, low duty cycle sources which are common in the VUV.
Supported by NASA.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.