Simple ultraviolet calibration source with reference spectra and its use with the Galileo orbiter ultraviolet spectrometer
J. M. Ajello, D. E. Shemansky, B. Franklin, J. Watkins, S. Srivastava, G. K. James, W. T. Simms, C. W. Hord, W. Pryor, W. McClintock, V. Argabright, and D. Hall
J. M. Ajello,3
D. E. Shemansky,1
B. Franklin,3
J. Watkins,3
S. Srivastava,3
G. K. James,3
W. T. Simms,3
C. W. Hord,2
W. Pryor,2
W. McClintock,2
V. Argabright,2
and D. Hall1
1University of Arizona, Lunar & Planetary Laboratory, Tucson, Arizona 85721
2University of Colorado, Department of Astrophysical, Planetary & Atmospheric Science, Laboratory for Atmospheric & Space Physics, Boulder, Colorado 80309
3The other authors are with California Institute of Technology, Jet Propulsion Laboratory, Pasadena, California 91109.
J. M. Ajello, D. E. Shemansky, B. Franklin, J. Watkins, S. Srivastava, G. K. James, W. T. Simms, C. W. Hord, W. Pryor, W. McClintock, V. Argabright, and D. Hall, "Simple ultraviolet calibration source with reference spectra and its use with the Galileo orbiter ultraviolet spectrometer," Appl. Opt. 27, 890-914 (1988)
We have developed a simple compact electron impact laboratory source of UV radiation whose relative intensity as a function of wavelength has an accuracy traceable to the fundamental physical constants (transitions probabilities and excitation cross sections) for an atomic or molecular system. Using this laboratory source, calibrated optically thin vacuum ultraviolet (VUV) spectra have been obtained and synthetic spectral models developed for important molecular band systems of H2 and N2 and the n1P0 Rydberg series of He. The model spectrum from H2 represents an extension of the molecular branching ratio technique to include spectral line intensities from more than one electronic upper state. The accuracy of the model fit to the VUV spectra of H2 and N2 is sufficient to predict the relative spectral intensity of the electron impact source and to serve as a primary calibration standard for VUV instrumentation in the 80–230-nm wavelength range. The model is applicable to VUV instrumentation with full width at half-maximum ≥0.4 nm. The present accuracy is 10% in the far ultraviolet (120–230 nm), 10% in the extreme ultraviolet (EUV) (90–120 nm), and 20% in the EUV (80–90 nm). The n1P0 Rydberg series of He has been modeled to 10% accuracy and can be considered a primary calibration standard in the EUV (52.2–58.4 nm). A calibrated optically thin spectrum of Ar has been obtained at 0.5-nm resolution and 200-eV electron impact energy to 35% accuracy without benefit of models over the EUV spectral range of 50–95 nm. The Ar spectrum expands the ultimate range of the VUV relative calibration using this source with the four gases, He, Ar, H2, and N2, to 50–230 nm. The calibration of the Galileo orbiter ultraviolet spectrometer for the upcoming Jupiter mission has been demonstrated and compared to results from other methods.
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Low-Pressure Electron Impact EUV Calibration Relative Intensities of Argon at 200 eV and 0.5-nm Resolution*
Interval #
Wavelength Interval (nm)
Relative Calibration Area
I
46.8–49.8
0.178
II
49.8–52.8
0.193
III
53.4–56.4
0.380
IV
56.4–58.9
0.432
V
58.9–62.1
0.159
VI
65.3–68.6
0.533
VII
70.8–73.6
0.333
VIII
78.1–81.2
0.510
IX
81.2–84.2
0.814
X
85.5–89.4
1.941
XI
91.1–93.9
1.000
Relative uncertainty 35%. Foreground abundances for calibration intensities given in interval IX and X must be measured with abundances <2 × 1011 cm−2 since IX and X are Ar I resonance lines. Features I–VII and XI are independent of pressure since they are Ar II lines.
Tables (8)
Table I
Absolute Cross Sections of the Rydberg Systems, H Ly-α, H Ly-β and E, F Systems at 100 eV
Low-Pressure Electron Impact EUV Calibration Relative Intensities of Argon at 200 eV and 0.5-nm Resolution*
Interval #
Wavelength Interval (nm)
Relative Calibration Area
I
46.8–49.8
0.178
II
49.8–52.8
0.193
III
53.4–56.4
0.380
IV
56.4–58.9
0.432
V
58.9–62.1
0.159
VI
65.3–68.6
0.533
VII
70.8–73.6
0.333
VIII
78.1–81.2
0.510
IX
81.2–84.2
0.814
X
85.5–89.4
1.941
XI
91.1–93.9
1.000
Relative uncertainty 35%. Foreground abundances for calibration intensities given in interval IX and X must be measured with abundances <2 × 1011 cm−2 since IX and X are Ar I resonance lines. Features I–VII and XI are independent of pressure since they are Ar II lines.