Electric lamp and discharge devices – With optical device or special ray transmissive envelope – Polarizer or special ray transmission
Patent
1990-09-10
1992-05-26
Yusko, Donald J.
Electric lamp and discharge devices
With optical device or special ray transmissive envelope
Polarizer or special ray transmission
313635, 313637, 359359, 359580, H01J 6140
Patent
active
051171503
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a deuterium lamp with a discharge bulb of quartz glass for spectral analyzers, in particular spectral photometers, in which the radiation produced passes through a portion of the bulb.
BACKGROUND OF THE INVENTION
Deuterium lamps of the type defined above are known for instance from the W. C. Heraeus GmbH brochure entitled "Deuteriumlampen--Baureihe D 800/900" [Deuterium Lamps--Series D 800/900](D 310 686/2C 7.86/VN Ko). These deuterium lamps furnish a continuous, line-free spectrum in the ultraviolet spectral range between 160 and 360 nm. They are used particularly in photometry equipment, preferably spectral analyzers. The bulb of these deuterium lamps is of quartz glass, and if synthetic quartz glass is used, the lamp bulb becomes transparent for wavelengths of up to approximately 160 nm. Deuterium lamps of this previously known type have proved to be excellent in operation. They are distinguished by a long service life and particularly high radiation stability. However, it has been found that the radiation noise of the lamp is a limiting factor when these lamps are used for detecting very slight concentrations. The known deuterium lamps have a radiation noise level of approximately 2.times.10.sup.-4 AU (AU=absorption units).
SUMMARY OF THE INVENTION
It is the object of the present invention to further reduce the radiation noise level of the deuterium lamps defined at the outset above, while retaining the aforementioned favorable properties of the known deuterium lamps.
For deuterium lamps of the type defined at the outset above, this object is attained in accordance with the invention in that at least the aforementioned portion of the bulb has on its surface a multiple interference filter layer of alternating aluminum oxide and either silicon dioxide or magnesium fluoride; the physical thickness of each layer is in the range from 10 to 70 nm, and the first effective layer of the interference filter, facing the bulb surface, comprises aluminum oxide, and the multiple interference filter layer has an absorption edge at a wavelength from approximately 190 to 200 nm, but has maximally high transmission for wavelengths greater than 200 nm. In the deuterium lamps according to the invention, it has proved successful to provide at least 10 pairs of layers for the multiple interference filter layer. The term "pair of layers" is understood to mean a combination of one aluminum oxide layer and one layer of either silicon dioxide or magnesium fluoride. According to the invention, the multiple interference filter layer has a steep absorption edge in the wavelength range from approximately 190 to 200 nm.
By embodying the deuterium lamp according to the invention, the radiation noise level can be reduced by over 50%, at least. If the number of pairs of layers is increased, a reduction by approximately one order of magnitude was even attainable; that is, it was possible to lower the radiation noise level to a value of 2 .times.10.sup.-5 AU The deuterium lamps provided with interference filters embodied in accordance with the invention are distinguished not only by the steep absorption edge in the range from 190 to 200 nm, but also by the fact that at a wavelength greater than 200 nm, they have an extraordinarily high transmission for the longer-wave UV radiation, or in other words precisely the radiation that one seeks to use for performing spectral analysis tests. In terms of their service life, the lamps according to the invention have not changed, compared with deuterium lamps without a multiple interference filter layer; nor has the transmission of UV radiation at a wavelength of greater than 200 nm undergone any disadvantageous change, even when operated for periods of over 1500 hours. Another advantage of the deuterium lamps according to the invention that should be stressed is that ozone formation, which not only impedes spectral analysis but may also harm persons working with it, does not take place.
Interference filter layer combinations of aluminum oxide and silicon dioxide have
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E. T. Fairchild, "Interference Filters for the VUV (1200-1900 .ANG.", Applied Optics, vol 12, No. 10, pp. 2240-2241, Oct. 73.
Original Hanau Quarzlampen GmbH, datasheet entitled "Deuterium-Lampe D60 & D60F", Sep. 1973.
W. C. Heraeus GmbH, Original Hanau Division, datasheet entitled "Deuteriumlampen-Baureihe D800/900" (undated).
Kremmling Horst
Lotz Hans-Georg
Schwarz Werner
Thomas Gunter
Hamadi Diab
Heraeus Instr. GmbH & Leybold AG
Yusko Donald J.
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