Method and device for producing rod lenses

Abstract

A method for producing rod lenses with an enveloping diameter of the rod lens face of up to 200 mm and an edge length of at least 800 mm. The method is characterized in that fabrication is performed from a cylindrical rod lens element made from synthetic quartz glass material configured as a fused silica ingot. This is performed using a flame hydrolysis method with a direct one stage deposition process of SIO.sub.x particles from a flame stream onto die that rotates and is moveable in a linear manner with respect to the flame stream.

Claims

1. A method for producing rod lenses with an enveloping diameter of a rod lens face of up to 200 mm and an edge length of at least 800 mm, comprising directly fabricating the rod lenses from a cylindrical fused silica ingot element prepared by generating synthetic quartz glass material SiO.sub.x particles in a flame hydrolysis nozzle and depositing the particles onto a rotating die in a direct, one-stage deposition process, and moving the rotating die away from the flame hydrolysis nozzle in a linear fashion with respect to a flame stream from the nozzle such that the distance from the flame of the flame stream and a surface of a forming silica glass layer on the ingot remains constant, wherein the fused silica ingot is free of bubbles, layers, inclusions, and cords over the edge length of the rod lens.

2. The method of claim 1, wherein the synthetic quartz glass material deposited in the deposition process has an OH content of more than 1,000 ppm and/or a H.sub.2 content of more than 0.8×10.sup.18 molecules/cm.sup.3.

3. The method of claim 1, wherein the synthetic quartz glass material deposited in the deposition process has an OH content of more than 1,200 ppm and an H.sub.2 content of more than 0.8×10.sup.18 molecules/cm.sup.3.

4. The method of claim 3, wherein the H.sub.2 content is about 1.2×10.sup.18 molecules/cm.sup.3.

5. The method of claim 1, wherein the synthetic quartz glass material deposited in the deposition process has maximum transmissivity for ultraviolet radiation in the wave length range of 193-400 nm.

6. The method of claim 1, wherein the fused silica ingot element has a high axial refractive index homogeneity with a refractive index deviation of 4.Math.10.sup.−6 or less, measured directly after preparation of the fused silica ingot element.

7. The method of claim 1, wherein the synthetic glass material deposited in the deposition process has a value of stress double refraction of less than 5 nm/cm.

8. The method of claim 1, wherein the synthetic glass material deposited in the deposition process has a value of stress double refraction of less than 3 nm/cm.

9. The method of claim 1, wherein the rod lens edge length is ≧1500 mm.

10. The method of claim 1, wherein the fused silica ingot element is prepared in a muffle furnace, with an internal temperature of 1100° C. to 1300° C.

11. The method of claim 10, wherein the internal temperature is maintained by monitoring and adjusting the temperature of an exhaust gas exiting the muffle furnace.

12. The method of claim 10, wherein a distance between an inner wall of the muffle furnace and an enveloping lateral surface of the cylindrical rod element is from 40-75 mm.

13. The method of claim 10, wherein a distance from an inner wall of the muffle furnace and a melting surface of the cylindrical rod element is from 10-25 mm.

14. A method for producing a cylindrical rod ingot suitable for directly producing a rod lens, comprising generating synthetic quartz glass material SiO.sub.x particles in a flame hydrolysis nozzle and depositing the particles onto a rotating die in a direct, one-stage deposition process, and moving the rotating die away from the flame hydrolysis nozzle in a linear fashion with respect to a flame stream from the nozzle such that the distance from the flame of the flame stream and a surface of a forming silica glass layer on the ingot remains constant, wherein the cylindrical rod element is free of bubbles, layers, inclusions, and cords over a length of at least 800 mm.

15. The method of claim 14, wherein the synthetic quartz glass material amount deposited in the deposition process has maximum transmissivity for ultraviolet radiation in the wave length range of 193-400 nm.

16. The method of claim 14, wherein the method takes place in a muffle furnace, with an internal temperature of 1100° C. to 1300° C.

17. The method of claim 16, wherein the internal temperature of the muffle furnace is maintained by monitoring and adjusting the temperature of an exhaust gas exiting the muffle furnace.

18. The method of claim 16, wherein a distance between an inner wall of the muffle furnace and an enveloping lateral surface of the cylindrical rod element is from 40-75 mm.

19. The method of claim 16, wherein a distance from an inner wall of the muffle furnace and a melting surface of the cylindrical rod element is from 10-25 mm.

20. The method of claim 13, wherein an extension is laterally connected to an end muffle furnace remote from the flame hydrolysis nozzle, the extension having a length of at least 50 mm.

21. A method for producing rod lenses with an enveloping diameter of a rod lens face of up to 200 mm and an edge length of at least 800 mm, comprising: directly fabricating the rod lenses from a cylindrical fused silica ingot element prepared by generating synthetic quartz glass material SiO.sub.x particles in a flame hydrolysis nozzle and depositing the particles onto a rotating die in a muffle oven in a direct, one-stage deposition process; providing a uniform muffle oven temperature of 1000° C. to 1300° C. during the deposition process; keeping a constant distance between a melting surface of the deposited fused silica ingot and an inner wall of the muffle oven; and moving the rotating die away from the flame hydrolysis nozzle in a linear fashion with respect to a flame stream from the nozzle such that the distance from the flame of the flame stream and a surface of a forming silica glass layer on the ingot remains constant, wherein the fused silica ingot is free of bubbles, layers, inclusions, and cords over the edge length of the rod lens.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is subsequently described in more detail based on an embodiment. FIGS. 1 and 2 are being used for further illustration. Identical reference numerals are being used in the figures for identical or equivalent components wherein:

(2) FIG. 1 illustrates a basic muffle configuration; and

(3) FIG. 2 illustrates an oven extension.

DETAILED DESCRIPTION

(4) The proposed flame hydrolysis method is performed in a muffle oven. The muffle oven includes a configuration that is known for ovens of this type. It is made from a tubular or tunnel shaped muffle 1 in which the deposition process is performed. Preferably the muffle has a multi shell wall configuration from a porous heat insulating material 1 a, in particular a fibrous and/or ceramic material, a concrete- or fire brick wall 1b and an inner fairing 1c made from a material that is sufficiently resistant with respect to high temperatures in particular aluminum oxide or silicon carbide.

(5) The muffle 1 has respective openings at its ends. One of the two openings is used for inserting a die 4. The opposite opening includes a burner 2 inserted therein which can also be configured with plural flames. The burner 2 is configured with a feed line 3 for a reactant that includes silicon which is introduced in gaseous form into the burner portion and oxidized into silicon oxide SiO.sub.x. The silicon oxide particles thus formed are driven in the flame stream towards the die 4 and deposit on the die. The die 4 is rotatably supported, so that an even coverage of the die surface is provided with the particle flow. This forms a growing layer of synthetically generated quartz glass in the form of a fused silica ingot (FS-ingot) 5 on the surface of the die 4.

(6) The process is run so that the distance between the flame portions of the burner 2 and the surface of the forming quartz glass layer is substantially maintained constant. Thus, the die 4 is pulled back with a continuous speed so that a quartz glass cylinder or the FS-ingot 5 forms with an increasing length on the die 4. It represents the forming rod lens base element which can be removed, cooled tested and subsequently be directly used as a semi finished product for producing one or plural rod lenses immediately after the deposition process is completed.

(7) The method provides high temperature uniformity over the entire deposition process and for large portions of the rod lens element. A melting length that is as long as possible in the FS ingot is important, wherein inhomogeneitites can be effectively prevented in longitudinal direction of the FS-Ingot. Kiln temperatures in a range of 1,100-1,300° C. have proven advantageous, wherein the temperature is controlled through adjustment and monitoring of the exhaust air temperature. Thus an exhaust air temperature of 230-270° C. has proven useful.

(8) The distance b between the muffle inner wall and the melting surface of the deposited FS-ingot is preferably kept constant through a light beam monitoring. Distances of 10-25 mm have proven useful.

(9) Adjusting and preselecting a reproducible reaction cavity volume between the forming FS ingot and the muffle inside is advantageous. Herein respective different muffle geometries are used which provide a distance a between the enveloping surface of the FS-ingot and the muffle inner wall in a range of 40-75 mm.

(10) In this context an adapted and variably configured extension 7 of the oven cavity is advantageous which laterally connects to the actual muffle 1. An oven extension of this type is illustrated in FIG. 2. The oven extension additionally contributes to temperature consistency in the muffle cavity. The extension includes for example a length L of approximately 50-250 mm.

(11) It has become apparent that the method recited supra facilitates in particular producing rod length elements with a large ratio between edge length and height/thickness. Typical lengths of the rod length element are at least at 800 mm and can be 1500 mm and more without problems. Thus, the edge length L is many times greater than the height H or the thickness D for comparatively normal rod lenses.

(12) The synthetic quartz glass of the finished rod lens element is completely homogenous over its entire length without bubbles, layers, inclusions and cords. It includes a high content of OH groups of at least 1,000 ppm, in particular 1,200 ppm and more. The content of molecular hydrogen H.sub.2 is above 0.8×10.sup.18 molecules per cm.sup.3, typically 1.2×10.sup.18 molecules per cm.sup.3. The value of the stress double refraction is less than 5 nm/cm and is typically below 3 nm/cm. In axial direction a high refractive index homogeneity with a deviation of 4×10.sup.−6 and less is achieved. The glass material has a maximum transmissivity for light in the ultra violet spectral range, this means in a range of 193 to 400 nm over its entire length. Simultaneously this suppresses undesirable fluorescences under the influence of irradiated laser light in the finished rod lens.

(13) Without any problem two or plural rod lenses can be produces from a quartz glass cylinder (rod lens base element) which are essential identical with respect to their material properties irrespective from which section of the original cylinder the eventually provided rod lens has been cut.

(14) The invention was described based on exemplary embodiments. Other embodiments will be apparent to a person skilled in the art and can also be derived from the dependent claims.

(15) TABLE-US-00001 REFERENCE NUMERALS AND DESIGNATIONS 1 muffle 1a heat insulating material 1b concrete or fire brick wall 1c inner fairing 2 burner 3 feed line for reactive agent 4 die 5 FS-Ingot 6 melting surface 7 oven cavity extension a distance enveloping surface FS-ingot to muffle inner wall b distance melting surface to muffle inner wall L length of kiln cavity extension

(16) As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

(17) While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.