Hollow-cathode spectral light source with means to prevent high voltage arcing

#The present invention relates to spectral light sources, and more particularly to hollow-cathode type light sources.

#Hollow-cathode spectral light sources are used in atomic absorption spectroscopy. Such light sources provide high intensity, sharply defined spectral lines for many analytical applications. A conventional hollow-cathode type light source design is seen in U.S. Pat. No. 3,264,511. The spectral light is produced as a result of a concentrated discharge which takes place between an anode and the hollowed portion of the cathode. The hollowed portion of the cathode contains the atomic species which generate the desired spectral light output. The discharge must be confined to the hollow portion of the cathode in order to achieve efficient operation. The teaching of U.S. Pat. No. 3,264,511 was that an insulating disc should be positioned between the anode and cathode, with the disc having a central aperture aligned with the hollow portion of the cathode. An insulating means is also taught as being disposed between the anode lead-in and the exterior of the cathode.

#The insulating disc serves as the primary insulating means between the anode and the exterior of the cathode to insure that the discharge is confined to the cathode hollow. In order to facilitate assembly of the device, the insulating disc has a diameter which is less than the inside diameter of the glass envelope. There is thus some spacing between the outer edge of the disc and the glass envelope. This spacing is advantageous during evacuation of the envelope, since this is carried out through the base of the envelope.

#The sole FIGURE is an enlarged perspective view partly in section of the hollow-cathode spectral light source of the present invention.

#The present invention can be best understood by reference to the embodiment seen in the drawings. In the sole FIGURE the hollow-cathode spectral light source 10 has a generally cylindrical, hermetically sealed light transmissive envelope 12. A selected fill gas, such as neon or argon, is provided within the space defined by the envelope at a pressure of several torr. The envelope 12 is a vitreous material such as glass, and has a base 14 at one end, and a highly transmissive window 16 at the other end which is typically formed of quartz.

#A plurality of electrical lead-ins 18, 20, 22 are sealed through the base 14. One lead-in 18 is electrically connected to and supports a hollow-cathode 24. The hollowed portion 26 of the hollow-cathode 24 is at the end facing the window 16. The hollow-cathode is aligned along the longitudinal axis of the envelope. The lead-ins 20 and 22 support and are electrically connected to a ring anode 28 which is spaced from the hollowed portion 26 of the cathode 24. Ceramic insulating sleeves 30a, 30b are provided over the lead-ins 20 and 22 to insulate these lead-ins from the cathode. In the embodiment shown a first insulating disc 32 is provided between the anode and cathode. The insulating disc 32 is preferably a thin mica disc. The disc 32 is supported by ceramic sleeve portions 34 provided over the lead-ins 20 and 22. The disc 32 has a central aperture 36 aligned with the hollow portion of the cathode. The disc 32 is disposed transverse to the envelope longitudinal axis. A second insulating disc 38 may be provided about the hollow cathode 24, parallel to and closely spaced from the first disc 32.

#The discs 32 and 38 have diameters which are just less than inside diameter of the cylindrical glass envelope.