GB2044243A - A method of fabricating a gas laser tube assembly - Google Patents

Abstract

A laser tube assembly wherein the component portions of the assembly are held together and thereafter sealed using a glass frit suspended in a suitable vehicle. The prefabricated component portions of the laser tube assembly are held together by means of an appropriate fixture, glass frit first being applied at the appropriate junctions between the component portions. The fixtured assembly is then placed in an oven, the oven being brought up to a temperature that melts the glass frit and seals the component tube portions together. In internal mirror type lasers, wherein a metal end flange is joined to the ends of the glass laser envelope to form part of the overall laser tube assembly, the prefabricated metal end flange is positioned against each end of the glass laser envelope, glass frit being applied between one end of the flange and the ends of the glass envelope prior to the assembly being placed in the oven.

Description

SPECIFICATION A method of fabricating a gas laser tube assembly Gas laser tubes have been commercially available for a number of years and have found many applications, such as in supermarket scanners, facsimile devices, medical apparatus, surveying systems, computer printers, etc. Helium-neon gas lasers, in particular, have been most widely utilized in these applications.

Xerox Corporation has commercially introduced a facsimile transceiver device, sold as the 'Xerox' 'Telecopier' 200 transceiver, which records on plain paper. The transceiver employs a low-energy helium-neon laser and uses the xerographic principle to receive and print messages on ordinary, unsensitized paper. Basically, when the transceiver is in the transmit mode, the laser provides a small stable beam of lightto raster scan the original document. The reflected light is detected by a photo sensorwhich translates the white and black of the document to electrical logic levels which may be transmitted by a phone line to a remote transceiver set to the receive mode.The receiver transceiver directs the laser beam onto a xerographic drum and by electrically modulating the laser with "1" or "0" logic levels in synchronism with the transmitter produces a copy of the original.

Although gas lasers have found commercial acceptance as evidenced by its multiple applications described previously, lasers are still considered to be in their early stages of development and additional applications therefor await further laser improvements. A substantial drawback to the expanded use of lasers is that they are typically not mass produced and therefore the cost per tube is relatively high. In particular, present fabrication techniques require glassblowing skills. The obvious disadvantage is that this technique requires high skill operations which in itself tends to reduce the production rate for such tubes and to increase the costs and complexity associated therewith. The present invention therefore aims at providing a fabrication technique wherein the cost of laser tube fabrication and the complexity thereof are substantially reduced.

Accordingly, the present invention provides a laser tube assembly wherein the component portions of the assembly portions of the assembly are held together and thereafter sealed using a glass frit suspended in a suitable vehicle. In the process of forming the assembly the prefabricated component portions of the laser tube assembly are held together by means of an appropriate fixture, glass fit first being applied at the appropriate junctions between the component portions. The assembly is then placed in an oven, the oven being brought up to a temperature that melts the glass frit and seals the component tube portions together.In internal mirror type lasers wherein a metal end flange is jointed to the ends of the glass laser envelope to form part of the overall laser tube assembly, the prefabricated metal end flange is positioned against each end of the glass laser envelope, glass frit being applied between one end of the flange and the ends of the glass envelope prior to the assembly being placed in the oven.

Fora better understanding of the invention, reference is made to the following description which is to be read in conjunction with the accompanying drawings wherein: Figures lA-lEshowin a simplified manner the prior art method of fabricating gas laser tube assemblies; Figure 2 shows an exploded view of a gas laser tube fabricated in accordance with the present invention, and Figure 3 illustrates the component portions of the gas laser tube of the present invention held together by a fixture.

In orderto put the present invention in perspective, a description of a method presently utilized in laser tube fabrication will be first set forth. A comparison can then be made of the relative inexpensive and simple method for fabricating laser tubes which has been provided by the present invention.

The laser tube assembly, it should be noted, which results from the prior art techniques and that formed by the process of the present invention are essentally the same.

Further, although the method described will be with reference to fabricating helium-neon gas tubes, the method can be utilized for any type of gas laser tube, including, for example, helium-cadmium and argon gas laser tubes.

Figures 1A-1 E illustrate, in a simplified form, the typical steps which have been utilized in the prior art to fabricate lasertubes. In particular, the figures illustrate the basic fabrication technique which has been utilized by Xerox Corporation to manufacture helium-neon laser tubes.

In the initial step, an apertured flange member 10, preferably made of'Kovar', is positioned on a holding fixture (not shown). The flange 10 can be fabricated utilizing ordinary stamping machines.

In the second step (Figure 1 B), a length of precision cut glass tubing 12, which will form a portion of the envelope of the assembled gas laser tube, is mounted in a lathe (not shown). The sealing area 14 of flange 10 is cleaned and oxidized in a process to be described in more detail hereinafter. A bead of glass 16 is applied to the seal area 14 and glass tubing portion 12 is positioned in contact with bead 16.

A gas torch (not shown) is applied to the bead 16 as the lathe is rotated thereby to form a seal between flange 10 and tubing 12, thereby forming the anode envelope portion ofthe assembled gas laser tube. It should be noted atthis point that this sealing procedure is time-consuming and requires the precision skills of a person trained in the art of glass blowing.

In the step shown in Figure 1(C), a length of electrod wire 18, preferably made of'Kovar', has a glass bead 20 formed thereon. The electrode wire 18 is then inserted into glass tubing portion 22, the glass bead 20 being torch heated, forming a glass melt 24 which acts to seal wire 18 to glass portion 22, thereby forming an electrode assembly portion 26.

This portion is then positioned about glass envelope portion 12 (Figure 1(B)), and a hole 28 is blown in the envelope as assembly 26 is sealed to the envelope.

Because, as will be described hereinbelow, flange 10 will be considered the anode electrode in the fabri cated tube assembly, assembly 26 is referred to as the anode electrode assembly portion.

Figure 1(D) illustrates the step in forming the laser bore tube 30 with its associated support member. In particular, a precision cut cylindrical piece of glass tubing 31 has a flange or skirt member 32 sealed thereto by the glass bead/torch technique described hereinabove.

Figure 1(E) illustrates the right-hand, or cathode envelope portion 34 of the laser tube assembly. This portion is fabricated in the same manner in which the anode envelope shown in Figure 1(B) portion was fabricated, and includes precision cut glass tubing 36, 'Kovar' flange member 38 and cathode electrode assembly 40 which was fabricated in a similar manner the anode electrode assembly 22. The bore tube assembly 30 is placed on a fixture 42, of which only a portion is shown, and the bore tube assembly 30 is inserted concentrically within the laser tube envelope 41 which comprises envelope portions 12 and 36. The disc shaped member 32 is positioned adjacent the area 46 wherein the anode and cathode envelope portions 12 and 36 are joined together.A glass bead 48 is applied around the circumference of the joined envelope ends, the lathe material holding the assembly being rotated. Atorch is applied to glass bead 48, causing the envelope portions 12 and 36 to be sealed to each-other, the top of the disc 32 in turn being sealed to the tube envelope at area 46.

At this point in the laser tube fabrication process it can be seen that the steps required are complex and require relatively large amounts of time and the skills of a glassblower. In contradistinction thereto, the process of the present invention described hereinbelow with reference to Figure 2 can be accomplished quickly and economically without the skills required of a glassblower.

Figure 2 is an exploded view of a gas laser tube fabricated in accordance with the reachings of the present invention. The figure has been simplified for purposes of clarity and understanding.

Metal end flanges 50 and 52, typically made from 'Carpenter' 49 alloy, can be fabricated by standard type stamping machines. Glass tubing portions 54 and 56, which when assembled will comprise the laser tube envelope, are formed from standard glass stock, such as 0120 glass, and are cut to very close tolerances on a wet wheel machine. A length of cylindrical glass tubing 58, which forms the laser bore tube, is similarly fabricated. A glass disc member 60, which forms the support member for the bore tube 58 within the tube envelope, and an impedance means to force the lasertube discharge through the bore tube 58, is positioned around the bore tube 58 as illustrated. Glass frit 62 is thereafter applied to the assembly as shown in the figure.In particular, frit 62 is placed on the flat side of metal flange 50, on the adjacent end of tube portion 54, at the contact area between bore tube 58 and glass disc 60, at the ends of tube portions 54 and 56 which will contact glass disc member 60 when assembled, at the other end of glass tube portion 62 and the flat end of flange member 52. It should be noted that cathode and anode electrode pins couid be formed on the envelope itself, as shown in Figure 1, in lieu of the electrode connections shown in Figure 2. A nic kel or copper evacuating tube 64 is formed in flange 52 and utilized both to evacuate the assembled tube and thereafter to fill the tube with the lasing medium gas.

The portions 50, 52, 54, 56,58 and 60 of the laser tube are then positioned on an appropriate fixture, such as fixture 70 shown in Figure 3, and then placed into a batch oven (not shown). The oven temperature is then raised to a temperature that melts the glass frit 62, thereby sealing the metal and glass portions together.

The fixture 70 comprises end members 72 and 74, preferably disc shaped, and rods 76 and 78 secured to end member 72. The ends of rods 76 and 78 are securable in apertures 80 and 82 formed in end member74, end member 74 being detachable from the structure comprising end member 72 and rods 76 and 78. Secured to end member72 is a cylindrical member, or mandrel 84, member 84 having a further extension 86 of a smaller diameter thereon. Secured to end member 74 is a cylindrical member, or mandrel 88, member 88 having a further extension 90 of a smaller diameter thereon. As shown, the flange members 50 and 52 are supported on members 84 and 88, respectively, envelope portions 54 and 56 are positioned and held as shown by the fixture structure and the tube 58 is supported by extensions 86 and 90.The two piece fixture shown, preferably made of stainless steel, holds the lasertube components in the postions shown and the tube 58 concentric with the flanges 50 and 52. When placed in the oven, the fixture 70 is positioned vertically (end member 74 above end member 72) therein. End member 74 is weighted to press the laser tube components together (pressure-flow method) to make the seal and hold the linear dimensions.

A helium-neon laser tube was typically fabricated as follows: (1) the materials, both glass and metal, which comprise the laser assembly are selected to be closely matching in thermal expansion. In the preferred embodiment, metal flanges 50 and 52 were fromed from 0.020 inch thick 'Carpenter' 49 metal, the term utilized by the Carpenter Steel Company, to describe a metal alloy comprising 49% nickel and 51% iron, and the glass tubing selected comprised Corning code number 0120, manufactured by the Corning Glass Works, Corning, New York (glass tubing sections 54 and 56 were 25.4mm in diameter and member 58 had a bore 2.84mm in diameter).

(2) Metal flanges 50 and 52 were degreased in an acetone bath, fired in wet hydrogen at 1 0000C for approximately 30 minutes and then vapor blasted with pure aluminum oxide to a matte finish at the seal area.

(3) The glass frit (or solder glass) 62, selected to be No.89 'Pyroceram' a finely powdered glass composition, manufactured bytheCorning Glass Works Company, was applied to the assembly portion as shown. The glass frit, is held in suspension by a low viscosity vehicle, such as amylacetate containing approximately one percent nitrocellulose binder.

(4) The entire assembly, as shown in the figure, was positioned in a fixture, the fixture being utilized to hold the component parts in the assembled position, and thereafter placed in a batch oven.

(5) After the batch oven is raised to the temperature required to melt the glass frit (approximately 4400C), the portions are then sealed to each other and the assembly similar to that shown in Figure 1 (E) is produced.

In particular, the steps for forming the seal are as follows: The glass frit slurry is allowed to dry for a period of approximately 15 hours to form a hardened powder.

The amylacetate is substantially volatilized during the drying process and the hardened powder excess dressed by standard techniques. The assembly is then placed in a fixture and then put into an oven, the fixture being arranged to hold the laser tube portions to very close tolerances.

The temperatures of the oven is then brought to approximately 350"C for about 30 minutes to burn off any organic binders in the hardened powder. The temperature then is increased to the fritting temperature of approximately 440"C for 50 minutes, during which time the hardened powder, including the glass frit, surrounds and wets the contacting areas of the portions and permits the formation of a seal and subsequent devitrification. The oven is then cooled slowly to approximately 150 C whereby the portions are hard sealed to each other.

Although not shown in the Figure, lasertube mirror assemblies, are welded by standard techniques to metal flanges 50 and 52, thereby providing an internal mirror type gas laser tube.

The fabricated laser tube assembly, including the laser tube mirror assemblies, is then baked and evacuated to a low pressure to produce outgassing of the envelope and associated parts before the envelope is filled with the lasing gaseous medium through tube 64.

Claims (6)

1. A method for fabricating a gas laser tube assembly from a plurality of individual component portions, comprising the steps of: applying a sealing material at predetermined areas on individual component portions; assembling said individual component portions on a fixture in their desired final positions; placing said fixture with its component portions thereon in an oven, and energizing said oven in a manner such that a heating cycle is applied to said component portions whereby said sealing material melts and thereafter causes each said component portion to be sealed to an adjacent component portion.

2. The method as defined in Claim 1 wherein said sealing material comprises a glass frit.

3. The method as defined in Claim 1 or 2 wherein said component portions include a glass envelope having members sealed to each end thereof.

4. The method as defined in Claim 3 wherein at least one end member is an apertured metal flange.

5. The method as defined in Claim 4 wherein apertured mirror end assemblies are fixed to said apertured metal flanges to form an internal mirror type laser tube.

6. A gas laser tube assembly fabricated in accordance with the method of any preceding claim.