Light Source

Abstract

A light source to be powered by microwave energy, having a dielectric body or fabrication of material lucent for exit of light therefrom, a receptacle within the dielectric body or fabrication, and a lucent microwave-enclosing Faraday cage surrounding the dielectric body or fabrication. The dielectric body or fabrication within the Faraday cage forms at least part of a microwave resonant cavity. A sealed plasma enclosure of lucent material within the receptacle has a means for locating the plasma enclosure within the receptacle with respect to the dielectric body or fabrication.

Claims

1. A light source to be powered by microwave energy, the source having: a dielectric body or fabrication of material which is lucent for exit of light therefrom, a receptacle within the dielectric body or fabrication, a lucent, microwave-enclosing Faraday cage surrounding the dielectric body or fabrication, the dielectric body or fabrication within the Faraday cage forming at least part of a microwave resonant cavity, a sealed plasma enclosure of lucent material within the receptacle within the dielectric body or fabrication, means for locating the plasma enclosure within the receptacle with respect to the dielectric body or fabrication, wherein the means for locating the plasma enclosure comprises: one or more recesses in the body or fabrication at the receptacle and one or more complementary formations on the enclosure, the arrangement being such that in use the formation(s) engage in the recess(es) and maintain the enclosure centred in the receptacle with a regular air gap therebetween.

2. A light source according to claim 1, wherein the dielectric body is formed of a single piece of lucent material.

3. A light source according to claim 2, wherein the receptacle is formed by a through bore.

4. A light source according to claim 1, wherein the dielectric body is formed by a front wall, a back wall and a circumferential wall, the light source further comprising a backing disc adjacent the back wall.

5. A light source according to claim 4, wherein the receptacle is formed by a tube fused to the front wall at a first end and the back wall at a second end.

6. A light source according to claim 1, wherein the plasma enclosure is formed of a drawn tube.

7. A light according to claim 6, wherein the tube is sealed hemispherically at the diameter of the tube.

8. A light source according to claim 1, wherein the dielectric body and the plasma enclosure are fabricated of the same material.

9. A light source according to claim 6, wherein the material is quartz.

10. A light source according to claim 1, wherein the formation is a strand of material extending longitudinally around the plasma enclosure.

11. A light source according to claim 1, wherein the recess is a pair of opposing longitudinal recesses in the receptacle.

12. A light source according to claim 11, wherein the formation is a pair of opposing longitudinal strands of material fused to the plasma enclosure.

13. A light source according to claim 10, wherein the strand is the same material as that of the enclosure.

Description

[0051] To help understanding of the invention, two specific embodiments thereof will now be described by way of example and with reference to the accompanying drawings, in which:

[0052] FIG. 1 is a cross-sectional view of a light source of the invention on one central longitudinal plane;

[0053] FIG. 2 is a similar view on an orthogonal central plane;

[0054] FIG. 3 is a rear view of the crucible of the FIG. 1 light source;

[0055] FIG. 4 is a corresponding rear view of the capsule of the FIG. 1 light source; and

[0056] FIG. 5 is a view similar to FIG. 1 of a second embodiment of a light source of the invention.

[0057] Referring to FIGS. 1 to 4 of the drawings, a light source 1 has a base 2 for supporting a lucent crucible 3. The base is of round aluminium having a ceramic insert 4 in it. The insert has an indent 5 for an end 6 of an enclosure/bulb/capsule 21 and a bore through which a microwave transmitting antenna 8 extends. A mesh Faraday cage 9 surrounds the crucible in contact with it and is screwed 10 to the base, thereby holding the crucible on the base. These features are in accordance with our current production, except that at present the crucible is fabricated to have a central, sealed, excitable-material-containing void.

[0058] The crucible is of fused quartz, 20 mm long between end flats 11 and 49 mm in diameter.

[0059] In accordance with the invention, we provide the loose capsule or bulb 21 received in a central receptacle 22 in the crucible. Our conventional excitable material void in a bulb was of the order of 4 mm internal diameter, which corresponds in embodiments where it was of tube fabricated into the crucible, to a 6 mm outside diameter. We have referred to such a thing as a bulb. In so far as the capsule 21 is of 10 mm outside diameter, we prefer to call it a capsule.

[0060] The central receptacle is a nominal 10 mm bore, polished out to a 10.6 mm to provide a 0.3 mm air gap all round with the 10 mm OD capsule centred in the bore. On either side of the receptacle a pair of half moon recesses 23 are machined at opposite sides of the inner orifice 24 of the receptacle. They extend 2 mm in from their end flat and 2 mm radially. Their extent is approximately 75. They are equally angularly spaced with respect to a bore 12 in the crucible for the antenna (and one of them would intercept the bore if they were not so spaced.)

[0061] The capsule has a length at 10 mm diameter substantially equal in length to the 20 mm thickness of the capsule. Its front end is domed and the Faraday cage has a central aperture 14 to accommodate its slight protrusion. At the opposite end it has the 7 mm domed end to be received in the indent 5. At the full 10 mm diameter, immediately inwards of this dome, it has two 1 mm diameter, 5 mm long strands of quartz partially-circumferentially fused on around opposite sectors of the tube. These formations fit in the half moon recesses and locate the capsule both longitudinally and centrally in the receptacle, to establish the nominal 0.3 mm clearance between the capsule and the receptacle. When the capsule, crucible and Faraday cage are all assembled to the base, the strands are held bottomed in the recesses.

[0062] In a second embodiment, the crucible is replaced by a quartz fabrication 103, having front and back walls 111,112, a circumferential wall 113. A central tube 114 is provided to form a receptacle for a capsule. The walls and tube are fused together. The back wall has an aperture 115, oversize with respect to the bore of the receptacle tube 114, to provide an annular recess 116 for the formations of the enclosure. The fabrication has a lower volume average dielectric constant than the solid crucible, but this is compensated for by a back-up piece of alumina 117 through which an antenna extends centrally.

[0063] The invention is not intended to be restricted to the details of the above described embodiments. For instance, where a continuous recess such as the recess 116 is provided, the enclosure formation can be continuous as for instance a 360 ring of fused on strand or a small upset of the capsule material.