A UNITED STATES NBS TECHNICAL NOTE 496 DEPARTMENT OF COMMERCE PUBLICATION Rare Gas Resonance Lamps NATIONAL BUREAU OF STANDARDS The National Bureau of Standards ' was established by an act of Congress March 3, 1901. Today, in addition to serving as the Nation's central measurement laboratory, the Bureau is a principal focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. To this end the Bureau conducts research and provides central national services in four broad program areas. These are: (1) basic measurements and standards, (2) materials measurements and standards, (3) technological measurements and standards, and (4) transfer of technology. 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Virginia 22151. UNITED STATES DEPARTMENT OF COMMERCE Maurice H. Stans, Secretary NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director NBS TECHNICAL NOTE 496 ISSUED OCTOBER 1969 Nat. Bur. Stand. (U.S.), Tech. Note 496, 55 pages (Oct. 1969} CODEN: NBTNA Rare Gas Resonance Lamps R. Gorden, Jr., R. E. Rebbert, and P. Ausloos Physical Chemistry Division Institute for Materials Research National Bureau of Standards Washington, D.C. 20234 NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be listed or referred to in the open literature. For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C, 20402 - Price 60 cents Contents Page I. Introduction 1 II. General Design Characteristics 4 III. Procedure for Filling Rare Gas Resonance Lamps 7 IV. Actinometry 10 A. Apparatus and Procedure for the Measurement of Saturation Ion Currents 10 B. Extinction Coefficients and Ionization Quantum Yields for Various Substances 12 V. Xenon, Krypton and Argon Resonance Lamps 16 A. Transmission of Windows 16 B. Operational Characteristics 18 VI. Helium and Neon Resonance Lamps 20 A. Aluminum Windows 20 B. Operational Characteristics 25 1. Spectral Purity of Helium and Neon Lamps 2 5 2. Intensity of Neon and Helium Lamps 27 a) Effect of Helium and Neon Pressure ... 27 b) Effect of Power ana Distance of Discharge from Window 28 VII. References 30 li Rare Gas Resonance Lamps R. Gorden, Jr., R. E. Rebbert and P. Ausloos Rare gas resonance lamps having high spectral purity, high intensity, and long lifetimes have successfully been manufactured. The design and filling procedure for these lamps is described in detail. Particular operational characteristics of the xenon, krypton, argon, neon, and helium resonance lamps are also given. Windows suitable for use with each of these lamps are described, with particular emphasis given to the procedure for fabricating thin aluminum windows for use with neon and helium lamps. In addition, a method for determining extinction coefficients and ionization quantum yields based on the mea- surement of saturation ion currents is described. Key words: Resonance lamps; rare gases; photo- chemistry; photoionization; extinction coefficients; ionization quantum yield; aluminum window; saturation ion current. I. Introduction Light sources for use in vacuum ultraviolet photochemistry, photo- electron spectroscopy, as well as other applications, which utilize the emission of the characteristic resonance lines from excited rare gas atoms Til* (see Table I) have now been in use for a number of years. L J The rare gas resonance lamps fall into two categories according to their design; namely, those which have windows and those which are windowless. Enclosed lamps, utilizing windows which are transparent in the appropriate wavelength region, are generally fairly simple to make and to use, but until now have been restricted to the energy region including xenon, krypton, and argon resonance radiation because there was no readily available window material Figures in brackets indicate the literature references on page 30 TABLE I Lowest Resonance Emissions and Ionization Energies of the Rare Gases Resonance Emission Ionization Energy Gas (eV) (A) (eV) (A) He 21.22 584.3 24. 59 504.3 Ne 16. 85 73 5.8 21. 56 574.9 16. 67 743.7 Ar 11. 83 1048.2 15.76 786.7 11. 62 1066.7 Kr 10 64 1164.9 14.00 885.6 10 03 1235.8 Xe 9 57 1295.6 12.13 1022.1 8 44 1469.6 . 1 which would transmit photons of energy higher than 11.8 eV. Windowless lamps, on the other hand,, can utilize the rare gases which emit higher energy radiation, but are much more complicated in design since they require differential pumping and impose severe limitations on the pressure of the gas to be irradiated. It has long been known that certain metals, such as tin or aluminum, [21 or oxides such as SiO, will transmit high energy photons. J The require- ments of nuclear physics and electron microscopy have spurred the develop- ment of techniques for forming thin aluminum films supported on very fine mesh screens. If these films are sufficiently thin, yet sufficiently strong, they can be used as windows for rare gas resonance lamps. Recently, 3 1 the use of such a window on a "continuous plasma" helium lamp was reported; Lf J the lamp design described in that publication is, however, fairly complicated and difficult to fabricate and use. In this laboratory, enclosed microwave-operated xenon, krypton, and r 4 argon lamps have been in routine use for