GB2065960A - Structure of waveguide gas laser - Google Patents

Abstract

The elongated chamber in which laser gas is excited by an alternating electric field is formed of two spaced alumina blocks sandwiched between two alumina plates on the outer faces of which are formed electrodes for creating the electric field. The waveguide structure 100 thus formed is held between two ceramic blocks 132 and 134 which are clamped between shelves 158 formed integrally with an extruded tube 150. To permit assembly the tube has sufficient resilience to enable the distance between the shelves 158 to be increased by squeezing the sides of the tube, thereby enabling the guide structure to be inserted. <IMAGE>

Description

SPECIFICATION Structure of waveguide gas laser The present invention relates to a waveguide gas laser and is concerned particularly with the mechanical structure thereof.

European Patent Application No. 79100034 as published on 8th August 1979 under No.

0003280 describes a waveguide laser excited by means of radio frequencies in the range of 30 Mhz to 3 Ghz and in which a laser gas is disposed in an elongated chamber and a discharge is established by application of an alternating electric field to the chamber along a direction transverse to its length.

Our prior U.K. patent application No. 8030766 filed on 24 September 1980 describes a waveguide gas laser with RF excitation but in which the applied electric field extends longitudinally of the laser gas chamber. It also describes various ways in which the hot spot problem can be overcome, whether the waveguide gas laser has transverse or longitudinal excitation.

EPA Publication No. 0003280 describes in outline a waveguide gas laser structure consisting of a pair of opposed, elongated, aluminium electrodes between which the transverse exciting field is applied and a pair of opposed, elongated, dielectric members, for example of alumina, forming the sides of the laser gas chamber. U.K. application No. 8030766 describes a preferred structure for a longitudinally excited waveguide comprising a pair of aluminium oxide side blocks sandwiched between two ceramic plates, the electrodes being coated on the outer surfaces of the ceramic plates.

It is an object of the present invention to provide a housing and support for the waveguide structure of a gas laser which is suitable for mass production.

In accordance with the invention there is provided a waveguide laser structure comprising: means defining an elongated chamber of cross-sectional dimensions suitable for guiding laser light; a laser gas disposed in said chamber; means for establishing an alternating dielectric field in said chamber to establish the laser-exciting discharge in said laser gas; and an elongated elastic metal tube containing said elongated chamber defining means in compressive engagement along the entire length thereof.

The invention will now be described in more detail with the aid of an example illustrated in the accompanying drawings, in which Fig. 1 is a perspective view of a waveguide with electrodes for longitudinal excitation, Fig. 2 is a circuit diagram for the excitation circuit of the waveguide of Fig. 1, Fig. 3 is a cross-section of a waveguide laser structure in accordance with the invention incorporating the waveguide of Fig. 1, Fig. 4 is a perspective view of the housing for the structure of Fig. 3, and Fig. 5 is a side view of one end of the waveguide laser structure of Fig. 3.

Figs. 1 and 2 in the present application were Figs. 1 3 and 1 6 of U.K. Application No. 8030766 but will be described again here to provide a sufficient description of the present invention.

The waveguide 100 in Fig. 1 has a bore 102 which is formed by a pair of aluminium oxide side blocks 104 and 106 sandwiched between a pair of ceramic dielectric plates 108 and 110, which may also be composed of aluminium oxide. Each of the plates 108 and 110 is coated on its outside surface, as shown in Fig. 1 for the upper plate 108, with elongated electrodes 11 2 and 11 6 which respectively have tongues 114 and 11 8 projecting perpendicularly from them. The ends of the tongues 114 and 11 8 alternately overlap the region of the bore 1 02 and are spaced apart along the length of the bore to create a longitudinally directed field within the bore.At any instant of time the electrode 112 with its tongues 114, together with the corresponding electrode on the underside of the plate 11 0, is of opposite polarity to the electrode 11 6 and its tongues 11 8.

In the structure of Fig. 1, dimension "F" is typicaliy 0.02 inches, dimension "G" is typically 0.04 inches, and dimension "H" is typically 0.25 inches. In addition, waveguide bore 102 is square in crosssection with walls 0.08 inch in length defining the chamber.

Fig. 2 represents an electric circuit including various means for reducing or eliminating the hot spot problem as discussed in our earlier application. The electrodes are applied in the form of thin film metallization ho the outer surfaces of the dielectric plates 1 08 and 110 and the spacing of the electrodes from the laser gas chamber introduces a ballasting capacitance. A resonant conductor Lr is connected across the electrodes and the top and bottom electrode pairs of like polarity are interconnected by means of conductors 140 and 142, respectively, which also provide electrical interconnection to transformer 144. The transformer is connected to a voltage source Vq through a drive circuit consisting of a quater-wavelength line 146 having a characteristic impedance equal to or greater than 1.5 times the source impedance.In Fig. 2 it is assumed that the source impedance is 50 Ohms and that the characteristic impedance of line 146 is equal to or greater than 75 Ohms. A generator control device 148 is included to provide a delayed excitation power characteristic.

Figs. 3 to 5 show how the waveguide of Fig. 1 may be mounted in a housing in a manner which is conducive to lower cost mass production techniques. The waveguide 100 is sandwiched between alumina blocks 1 32 and 134 which provide insulation and prevent discharge outside the waveguide bore 102. The assembly is held in compression by a resilient tube 1 50 which serves as an evacuable housing prividing RF shielding and also as a heat sink. The tube 1 50 also serves to hold the waveguide in alignment with the optical system.

The tube 1 50 is of circular cylindrical form having an outer shell 1 52 and a pair of spaced-apart parallel shelves 1 58 extending longitudinally and parallel to the axis of cylinder 1 50. Shelves 1 58 are extended along the length of tube 1 50 from opposing locations along the interior periphery of shell 1 52 by respective necks 1 54. Each such shelf 1 58 includes a pair of parallel, generally perpendicular walls 156 to form rectangular grooves suitable for receiving and aliging the alumina blocks 132 and 134 of the waveguide structure.Typical dimensions of one embodiment of the invention employing the elastic metal tube 1 50 which may be readily manufactured by extruding materials such as 6063-T5 aluminium and the like, may be defined by Figs. 3 and 4 taken in conjunction with the following table:

REFERENCE DESIGNATION TYPICAL DIMENSIONS IN FIGS. 3 AND 4 (INCHES) K 0.475 +.01 0.390 i .01 M 0.125 +:01 N 0;375 +.01 S 0.025 * .005 P 1.25 +.01 Q 0.035 +.005 0.125 + .01 Typically, the distance between outside opposing surfaces of alumina blocks 1 32 and 134, is slightly larger than the preinstallation distance L.Accordingly, in order to insert the waveguide structure into the elastic tube 150, a compressive force is applied in planes 1 51 and 1 53 as indicated in Fig. 4, which causes the distance L between shelves 1 58 to increase to a distance suitable for receiving the waveguide structure. Thereafter, removal of the force applied in planes 151 and 153 results in a compressive force between the shelves applied through the waveguide structure in the range of 200 to 1000 psi. Consequently, it will be seen that the shelves 1 58 provide compressive alignment of the alumina blocks 132 and 134 and the entire waveguide structure by the spring action provided by the novel tube 1 50.In addition to prividing structural rigidity for the entire laser head configuration, tube 1 50 also provides substantially improved thermal contact with more efficient heat sinking action.

As shown in Fig. 5, the ends of tube 150 are chamfered at an angle 0 preferably equal to about 450. This results in the substantial advantage of providing automatic alignment for mirror mounts 1 60 which to those skilled in the art will recognize as a distinct advantage to the configuration of the present invention in which mirrored end surfaces are sometimes desirable. With mirror mount 1 60 also chamfered as shown in Fig. 5, mount 160 is readily vacuum dealed to the end of tube 1 50 by means such as a continuous solder bead 1 62 which may be applied around the entire circumference of the interface between mirror mount 1 60 and tube 1 50.

Claims (8)

1. A waveguide laser structure comprising: means defining an elongated chamber of cross-sectional dimensions suitable for guiding laser light; a laser gas disposed in said chamber; means for establishing an alternating electric field in said chamber to establish the laser-exciting discharge in said laser gas; and an elongated elastic metal tube containing said elongated chamber defining means in compressive engagement along the entire length thereof.

2. A waveguide laser structure as claimed in claim 1 in which the means defining an elongated chamber comprise a pair of electrically insulating blocks sandwiched between a pair of ceramic plates.

3. A waveguide laser structure as claimed in claim 2 in which the blocks and plates are all composed of alumina.

4. A waveguide laser structure as claimed in claim 2 or 3 in which the means for establishing an alternating field comprise electrodes coated on the surfaces of the said plates remote from the said chamber.

5. A waveguide laser structure as claimed in any of the preceding claims in which the means defining the chamber are sandwiched between a pair of electrically non-conductive blocks and the metal tube further comprises a pair of elongated spaced-apart parallel shelves extending from opposite points of the inner periphery of the tube along at least a portion of the length of the tube, the said shelves being in compressive engagement with the non-conductive blocks.

6. A waveguide laser structure as claimed in claim 5 in which each of the parallel shelves comprises substantially perpendicular walls to define a rectangular groove of width substantially equal to the width of said electrically non-conductive blocks for automatic alignment thereof.

7. A waveguide laser structure as claimed in claim 6 in which the eleastic metal tube is adapted to receive compressive force along a plane substantially parallel to said shelves for temporarily increasing the spacing between said parallel shelves without distorting their parallelism and without distorting said rectangular grooves.

8. A waveguide laser structure substantially as descrtibed with reference to Figs. 1, 3, and 4 of the accompanying drawings.