EP0780881A2 - Electrodeless discharge lamp - Google Patents

Abstract

An electrodeless low-pressure discharge lamp (1), in particular a deuterium lamp, has a cylindrically symmetrical diaphragm body (2), each of which contains a cavity (4, 5) on its end faces (8, 9); the two cavities (4, 5) are connected to one another by a bore (7) which serves as an aperture in order to constrict the plasma generated inside by coupling in a high-frequency electromagnetic field in order to increase the intensity of the radiation emitted. Both end faces (8, 9) of the cylinder-symmetrical diaphragm body (2) are provided with a hermetic seal, at least one of which is designed as an exit window (11); In a preferred embodiment, the electromagnetic field is coupled in capacitively by electrodes (13, 14) on the end faces, which have at least one opening (15) for the radiation to exit, provided that they are arranged adjacent to an exit window (11) . <IMAGE>

Description

The invention relates to an electrodeless low-pressure discharge lamp, in the lamp bulb of which a plasma is formed by coupling in a high-frequency electromagnetic field and radiation generated by the plasma emerges from the bulb along a predetermined radiation axis, a narrowed part of the lamp bulb being in the region of the plasma as a continuous bore along the Exit axis is provided.

From DE-OS 41 20 730 an electrodeless low-pressure discharge lamp is known, in the lamp bulb of which a plasma is formed by coupling in a high-frequency electromagnetic field and radiation generated by the plasma emerges from the bulb; a diaphragm body made of high-temperature-resistant material is arranged in the area of the plasma, which contains an opening for constricting the plasma area, the diaphragm body having an optical axis through the opening, along which the radiation emerges. In order to achieve sufficiently high radiation flows and radiation densities in the plasma constriction in the high-frequency field, the materials have to tolerate high wall loads so that they do not decompose, melt, release impurities at temperatures of more than 1500 ° Kelvin, or even as a result of thermal shock during insertion and Shut off the lamps.

According to DE-OS 41 20 730, boron nitride is preferably used as the material for the diaphragm body.

The heat removal from the area of the diaphragm body in which the plasma is constricted proves to be problematic due to the lamp bulb surrounding it; in the course of With increasing miniaturization of radiation sources, the known discharge lamp proves to be relatively complex in terms of its structure.

Furthermore, from GB-PS 10 03 873 an electrodeless high-frequency discharge spectral lamp is known, which contains a hollow lamp bulb made of translucent material, the lamp bulb being divided into two parts, which are connected to one another by means of a capillary feedthrough, and with electromagnetic arrangements for excitation a discharge are provided within the metal vapor located in the piston. The coupling of the electromagnetic energy for the discharge is maintained via a coil arrangement surrounding the lamp bulb, the actual ignition taking place via external electrodes.

According to the GB-PS, the considerable ignition problems prove to be problematic, so that additional electrodes have to be provided in the outer region of the lamp bulb, which initiate the ignition; a directed radiation along a preferred beam axis is not provided.

It is also a relatively complex construction, which stands in the way, particularly in the case of small construction types, as are desired with increasing miniaturization.

The object of the invention is to realize a low-pressure discharge lamp, in particular a low-pressure gas discharge lamp with a continuous spectrum with the highest possible radiance with high radiation stability; Furthermore, a simple mechanical structure should also be achieved with small geometric dimensions, so that it can be used as a light source in spectrophotometers and HPLC detectors, in particular, a spectral range of wavelength λ of 200-350 nm with high radiation stability is to be achieved.

The object is achieved by the characterizing features of claim 1.

In the case of gas discharge lamps in particular, the large spectral bandwidth in the continuum of the emitted radiation and the lack of impairment of the lamp atmosphere by introduced electrode material have proven to be advantageous; Furthermore, the simple geometric structure enables a very small size, so that the radiation source can possibly be applied to a printed circuit board.

Further advantageous refinements are specified in claims 2 to 12.

The possibility of providing a discharge lamp with two opposite radiation exit windows along the optical axis has proven to be particularly advantageous, since the spectrum of the radiation guided along the optical axis can be supplemented with the aid of an additional radiation source; in this way it is possible, for example, to superimpose additional portions of the visible and / or infrared spectrum of the UV radiation generated with the discharge lamp according to the invention.

• Figur 1 zeigt schematisch einen Längsschnitt durch eine erfindungsgemäße Gas-Entladungslampe mit einem elektrisch isolierenden Blendenkörper mit einseitigem Strahlenaustritt, wobei eine kapazitive Einkoppelung der Energie vorgesehen ist.
• Figur 2 zeigt eine modifizierte Ausführungsform der in Figur 1 dargestellten Lampe mit zweiseitigem Strahlenaustritt.
• Figur 3 zeigt schematisch die Anordnung einer kapazitiv angeregte Gas-Entladungslampe zusammen mit der elektrischen Schaltungsanordnung im Blockschaltbild.
• Figur 4 zeigt das Spektrum einer erfindungsgemäßen Entladungslampe mit Deuteriumfüllung.
• Figur 5 zeigt eine weitere Ausführungsform der Entladungslampe mit einem metallischen Entladungskörper im Längsschnitt.

The subject matter of the invention is explained in more detail below with reference to FIGS. 1 to 5.

• FIG. 1 schematically shows a longitudinal section through a gas discharge lamp according to the invention with an electrically insulating diaphragm body with one-sided radiation exit, with a capacitive coupling of the energy being provided.
• Figure 2 shows a modified embodiment of the lamp shown in Figure 1 with two-sided beam exit.
• FIG. 3 schematically shows the arrangement of a capacitively excited gas discharge lamp together with the electrical circuit arrangement in the block diagram.
• Figure 4 shows the spectrum of a discharge lamp according to the invention with deuterium filling.
• Figure 5 shows a further embodiment of the discharge lamp with a metallic discharge body in longitudinal section.

According to FIG. 1, the lamp 1 has a cylindrically symmetrical diaphragm body 2, the interior of which is divided into two sub-spaces 4 and 5 by a diaphragm 3. Both subspaces are connected to one another via an aperture 7 running along the cylinder axis 6. The two subspaces 4 and 5 are each closed off on the end faces 8 and 9 of the diaphragm body 2, the end face 8 being closed by a cover 10 made of the material of the diaphragm body, but the end face 9 having an exit window 11 made of a material which is radiation-permeable to the radiation generated, through which the radiation emerges along axis 6. Both end faces 8 and 9 are each provided with externally applied electrodes 13, 14, via which the excitation takes place by capacitive coupling of the energy into the interior of the lamp 1 in such a way that a plasma is generated in the subspaces 4, 5 and in the area of the aperture 7 is that is constricted in aperture 7 to increase the intensity. The Flat circular electrode 14 is provided along axis 6 with a radiation exit opening 15 arranged adjacent to exit window 11.

In a preferred embodiment, aluminum oxide is used as the material for the diaphragm body, while the radiation exit window 11 consists of quartz glass; the connection between the window 11 and the panel body 2 is created with the aid of glass solder, with a hermetically sealed closure by heat treatment; However, it is also possible to provide a sealed connection between the exit window 11 and the panel body by melting transition glasses. The diaphragm has a bore or diaphragm opening 7 with a diameter of 0.1 to 6 mm and has a length of 0.01 to 90 mm. The discharge vessel of lamp 1 is filled with deuterium at a cold filling pressure of 1 to 100 mbar. The outer diameter of the overall system consisting of electrode, discharge vessel and orifice is in the range from 5 to 80 mm.

In a further embodiment, aluminum nitride is used as the material for the diaphragm body; In addition to quartz glass, it is also possible to use glass or sapphire as the material of the exit window. Inside the lamp, aperture 3 fills the largest possible volume of the interior space consisting of subspaces 4 and 5. Both the rear part of the diaphragm body 2 and the diaphragm 3 can be mirrored within the lamp 1 and serve as a reflector, this being possible, for example, by lining the surfaces with a reflecting ceramic or by means of a metallic coating or metallization of the surface.

Furthermore, it is possible to design the diaphragm body in such a way that it has an axially symmetrical reflector geometry, such as e.g. is in the form of a hollow cone or truncated cone or in the form of paraboloids or hyperboloids.

It is also possible to use boron nitride, thorium oxide, beryllium oxide or polycrystalline diamonds as the material for the diaphragm body, these materials surviving high thermal wall loads and surviving at temperatures of more than 1500 ° Kelvin without impairment or deformation.

FIG. 2 shows a lamp 1 with a cylindrically symmetrical diaphragm body 2 ′, which, in contrast to the diaphragm body of FIG. 1, has an opening on its two end faces 8 and 9 along its optical axis 6, along the one through the diaphragm opening 7 leading cylinder axis 6, the two end faces 8 and 9 are each hermetically sealed by a radiation exit window 11 and 12; The electrodes 13, 14, which are provided along the radiator axis 6 with openings 15, 16 for the beam exit, are located on the beam exit windows. Here, too, as already described with reference to FIG. 1, the subspaces 4 and 5 can be provided with a reflective inner surface, moreover it is also possible to give the two subspaces 4 and 5 a reflector geometry, for example in the form of a hollow cone or truncated cone or the inner surface of a Assign paraboloid.

It has proven to be particularly advantageous that, by means of the arrangement shown in FIG. 2, a plurality of lamps can be arranged along a beam axis 6, it being possible to achieve an increase in the radiation intensity by superimposing the radiation emerging from the individual lamps.

According to FIG. 3, the circuit arrangement shown in the block diagram is provided for electrical control; The lamp symbolically represented under number 1 has on its end faces 8, 9 in each case an electrode 13, 14, which via an electrical control network 17 and a directional coupler 18 from a generator 19 - i.e. is capacitively excited by means of the electrodes 13, 14. The generator 19 is available for delivering powers in the range from 10 to 100 watts, the upper frequency limit being approximately 2.45 gigahertz and the lower one being 0.01 MHz. The directional coupler 18 is only used to decouple a measurement signal in order to optimize the control network 17.

In practice, the generator 19 is operated in the frequency range from 0.01 to 2450 megahertz, the directional coupler 18 located between the control network 17 and the generator 19 being connected to a vector voltmeter 20 for carrying out measurements.

In practice, the operation of the lamp in the frequency range 500 to 2450 megahertz has proven to be advantageous, the reactance of the lamp being the impedance of the supply line with the usual characteristic impedance of e.g. Approximates 50 Ω so that only small losses occur. In principle, however, any frequencies can be used to control the lamp, with lower frequencies, e.g. a direct adjustment of the generator output impedance is possible in the range from 100 kHz to 500 MHz, so that small losses also occur here.

FIG. 4 shows as curve A the spectral energy distribution over the wavelength λ when using the radiation arrangement according to the invention as a deuterium lamp. With a full width at half maximum From about 5 to 8 ° along the beam axis 6, the spatial radiation characteristic according to the invention is directed much more strongly than is the case with conventional deuterium lamps with a half-value width of over 36 °. The range of the continuum has a maximum at approximately 220 nm, the emission being line-free in the range from approximately 180 nm to approximately 360 nm.

According to FIG. 5, it is also possible to use a discharge lamp with a diaphragm body 2 'made of a high-temperature-resistant metal, such as molybdenum or tungsten; In this case, the electrically conductive diaphragm body is electrically insulated from the electrodes 13, 14 to avoid a short circuit, the electrical insulation of a first electrode 13 being effected by an annular insulating body 22, for example made of high-temperature-resistant ceramic material, such as aluminum oxide or aluminum nitride, while the second electrode 14 is insulated from the diaphragm body by the electrically insulating material of the exit window 11. The outlet window and the insulating body are attached and sealed, for example, by gas solders. This lamp can also be operated according to DE-OS 41 20 730 with deuterium with a cold filling pressure of 1 to 100 mbar, preferably at 9 mbar. The opening in the diaphragm body 2 has a length in the range from 0.01 to 90 mm, the diaphragm opening 7 designed as a bore containing a diameter in the range from 0.1 to 6 mm. In practice, in spite of the expectation of eddy current fields in the diaphragm body 2, no excessive heating can be determined.

Claims (12)

Electrodeless low-pressure discharge lamp, in the lamp bulb of which a plasma is formed by coupling a high-frequency electromagnetic field and radiation generated by the plasma emerges from the bulb along a predetermined radiation axis, a narrowed part of the lamp bulb being provided in the region of the plasma as a continuous bore along the exit axis, characterized in that the lamp bulb has a cylindrically symmetrical diaphragm body (2, 2 ') which is gas-tightly sealed along the beam axis (6) by at least one radiation-permeable outlet window (11, 12) applied as a separate component. Discharge lamp according to claim 1, characterized in that for the capacitive coupling of the electromagnetic field the diaphragm body (2, 2 ') along the beam axis (6) is provided at each end with a planar electrode (13, 14), at least one the electrodes (14) contains an opening in the axis (6) of the beam exit, which is arranged adjacent to the exit window (11). Discharge lamp according to claim 1 or 2, characterized in that the diaphragm body (2, 2 ') has an end face with an outlet opening, the end face facing away from the outlet opening having at least on its inside a surface reflecting the radiation generated. Discharge lamp according to Claim 1 or 2, characterized in that the diaphragm body (2, 2 ') has a continuous bore through both end faces (8, 9) along the optical axis (6), each with one of the electrodes (13, 14) opening (15, 16), each of the openings (15, 16) being arranged adjacent to a radiation exit window (11, 12). Discharge lamp according to Claim 4, characterized in that the beam axis (6) is arranged along the beam axis of an additional radiation source, radiation from the additional radiation source also being guided through the aperture (7). Discharge lamp according to one of claims 1 to 5, characterized in that the diaphragm opening (7) is circular, its diameter being in the range from 0.1 to 6 mm. Discharge lamp according to one of claims 1 to 6, characterized in that the diaphragm body (7) consists of aluminum oxide, aluminum nitride, boron nitride. Discharge lamp according to one of claims 1 to 6, characterized in that the diaphragm body (7) consists of thorium oxide, beryllium oxide or polycrystalline diamond. Discharge lamp according to one of claims 1 to 8, characterized in that the radiation exit window (11, 12) consists of quartz glass, UV-permeable glass or sapphire. Discharge lamp according to one of Claims 1 to 6, characterized in that the diaphragm body (2 ') consists of metal which is resistant to high temperatures, an electrically insulating component serving as an exit window (11;) between the electrodes (13, 14) and the diaphragm body (2'). 12) or as an insulating body (22). Discharge lamp according to one of Claims 1 to 10, characterized in that the filling is deuterium with a cold filling pressure of 1 to 100 mbar. Discharge lamp according to one of Claims 1 to 11, characterized in that the electrodes (13, 14) are connected to a high-frequency generator (19) which generates an excitation frequency in the range from 0.01 to 2450 MHz.

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