Flyable windowless calibration lamps for far-UV spectroscopy

We present the design of a pinhole lamp recently flown aboard two NASA/JHU sounding rocket missions as a wavelength standard for a far-UV spectrograph with a 900-1400 Angstrom bandpass. Lamp configuration, spectral output, gas supplies, payload accommodation and operation procedures are discussed. This lamp could easily be incorporated into future far-UV spectroscopic orbital missions and would benefit science return. We also discuss the use of Bayard-Alpert tubes (ionization gauges) as far-UV sources, which have the advantage of not requiring an external gas supply, At pressures between 10(-5) and 10(-7) Torr these tubes produce a strong emission Line spectra, caused by electron impact with residual gas atoms in the vacuum. Below 10(-7) Torr the residual gas line intensities have weaken enough to reveal the long wavelength tail of a 150 eV bremsstrahlung spectrum produced by electron impact onto tungsten grid. The use of ionization gauges in flat field and end-to-end calibration experiments is described. We show how an ionization gauge and spectrograph can be used as a real-time residual gas analyzer sensitive to atomic and molecular gas species that emit within the bandpass. Such a device could be useful in material processing and contamination control environments.