Laser oscillator

Abstract: The invention relates to a laser oscillator containing at least one pair of main electrodes (12, 13) within a laser tube (2). In accordance with a first aspect of the invention, a downstream one (13) of the main electrodes provided within the laser tube (2) which is located downstream, as viewed in the direction of flow of a laser gas, is substantially L-shaped, with its distal end (13b) being supported to extend in a direction to intersect with the axial direction of the laser tube (2). This improves the oscillation efficiency in exciting the laser radiation as compared with the prior art. According to the second aspect of the invention, a pair of ring-shaped pre-ionization electrodes (221) are disposed upstream of the main electrodes (212, 213) and there is provided a pre-ionization power supply (222) which applies a high voltage, which may be a pulse wave or an alternating voltage, across the pair of pre-ionization electrodes (221). The provision of the pair of pre-ionization electrodes enables a uniform pre-ionization, thus allowing a stabilised main discharge to be achieved across the main electrodes.

Description: The invention relates to a laser oscillator, and more particularly, to a laser oscillator containing at least one pair of main electrodes within a laser tube. A laser oscillator is known in the art as disclosed in Japanese Laid-Open Patent Application No.291, 391/94. This laser oscillator includes a plurality of sets of the main electrodes disposed in the axial direction of a laser tube, each main electrode being formed to be L-shaped and the distal ends of the main electrodes of the respective set being disposed so as to be opposite to each other. However, a disadvantage is pointed out with this conventional laser oscillator that it suffers from a poor oscillation efficiency. Also in this equipment, the opposite ends of a laser tube are supported by support members, and two sets of main electrodes are disposed axially within the tube. However, with a conventional laser oscillator which is provided with only main electrodes as mentioned, it may not be possible that a discharge across the main electrodes start up smoothly. Accordingly, in the prior art, there has been proposed a laser oscillator in which preliminary ionization electrodes are provided in addition to the main electrodes to produce a preliminary ionization before the main discharge takes place. An arrangement is proposed, as an example, in which a preliminary ionization takes place between the main electrode which serves as a cathode and a ring which serves a preliminary ionization electrode (see, for example, Japanese Laid-Open Patent Applications No.103, 889/89, No.15, 974/92 and No.22, 178/92). Secondly, there is also a proposal in which a preliminary ionization takes place between a pin which serves as a preliminary ionization electrode and the main electrode which serves as an anode (see, for example, Japanese Patent Publication No.105, 812/94). Thirdly, there is a proposal in which a preliminary ionization occurs between a ring serving as a preliminary ionization electrode and the main electrode which serves as an anode (see, for example, Japanese Patent Publication No.54, 864/95). However, with conventional arrangements which are provided with a preliminary ionization electrode, one of preliminary ionization electrodes is served by the main electrode. Accordingly, in such a conventional arrangement, there is a disadvantage that a uniform preliminary ionization of the laser tube cannot occur as the external diameter of the laser tube increases. Also, before a discharge across the main electrodes takes place, a d.c. high voltage source which is used as a power source for the main electrodes must be previously driven at a lower output. Patent Abstracts of Japan, vol 10, no 363 and JP 61160984 disclose a laser oscillator provided with a pair of cathodes and a pair of anodes together with, in the neighbourhood of the cathodes and located upstream thereof, a pair of parallel conductive auxiliary discharge electrode plates to rectify the flow of gas. The invention provides a laser oscillator comprising at least one pair of main electrodes disposed within a laser tube, a d.c. power source which applies a high voltage across the main electrodes, and gas feed means for feeding a gas into the laser tube, wherein a pair of ring-shaped preliminary ionization electrodes are disposed upstream of the main electrode, as viewed in the direction of the gas flow which passes through the laser tube, and a preliminary ionization power source is provided which applies either a pulse wave of high voltage or an a.c. high voltage across the preliminary ionization electrodes. With this arrangement, the preliminary ionization electrodes are provided separately from the main electrodes, and a preliminary ionization power source is provided separately from the d.c. source for the main electrodes. As a consequence, a uniform preliminary ionization can take place by the preliminary ionization electrodes to allow a stabilized main discharge across the main electrodes, independently from the magnitude of the diameter of the laser tube. In other words, if the external diameter of the laser tube increases, a uniform preliminary ionization is assured by the preliminary ionization electrodes. In addition, since the preliminary ionization power source is provided separately from the d.c. source for the main electrodes, the d.c. source from the main electrodes may be driven only when a laser radiation output is required. In other words, it is unnecessary to drive the d.c. high voltage source, which provides a power source for the main electrodes, previously at the lower output before the main discharge takes place. The invention will now be described in more detail and by way of example with reference to the accompanying drawings of which: Fig.1 is a view illustrating an embodiment of laser oscillator provided with some of the features of the invention, but excluding the preliminary ionization electrodes of an oscillator according to the invention; Fig.2 is a cross section to an enlarged scale of a left-hand laser tube 2 of the oscillator shown in Fig.1; Fig.3 is a cross section taken along the line III-III shown in Fig.2; Fig.4 is an enlarged view of a part shown in Fig.3; Fig.5 is a cross section taken along the line V-V shown in Fig.2; Fig.6 is an enlarged view of a part shown in Fig.2; Fig.7 is a cross section taken along the line VII-VII shown in Fig.2; Fig.8 is an enlarged view of a part shown in Fig.2; Fig.9 graphically shows the performance of the embodiment of Fig. 1 in comparison to the prior art; Fig.10 is a cross section of a modification of the laser oscillator shown in Fig. 1; Fig.11 is a cross section of an embodiment according to the invention; Fig.12 is an enlarged cross section of a part shown in Fig.11; Fig.13 is a cross section of a further embodiment according to the invention; Fig.14 is an enlarged view of a part shown in Fig.13; and Fig. 15 is a cross section of a yet further embodiment according to the invention. In the following description, the references to the laser oscillators illustrated in Figs.1 to 10 are included by way of introduction to the description of laser oscillators according to the invention shown in Figs.11 to 15. Initially referring to Fig. 1, there is shown a laser oscillator 1 having a pair of laser tubes 2, which have an identical construction, disposed in axial alignment. One end of each of the laser tubes 2, which are disposed opposite to each other, is supported by a manifold 3 which serves as a common support member. The other end of the respective laser tube 2 is supported by a manifold 4A or 4B which also serves as a support member. Laser gas feed means 5 feeds a laser gas to each of the laser tubes 2 through the manifolds 4A, 4B located at the opposite ends, and the laser gas from the respective laser tubes 2 are discharged externally from a central manifold 3 so as to allow a recirculation of the laser gas again into the respective laser tubes 2 through the manifolds 4A, 4B located at the opposite ends. The laser gas feed means 5 comprises a heat exchanger 6 disposed downstream of the central manifold 3 for cooling the laser gas which is discharged from the laser tube 2, and a blower 7 disposed downstream of the heat exchanger 6. Connection tubes 8 connect between the manifold 3 and the heat exchanger 6 and between the heat exchanger 6 and blower 7. The blower 7 is capable of delivering the laser gas in two directions. The laser gas from one of branches from the blower 7 is fed to one of the laser tubes 2 through a connection tube 8A, a heat exchanger 9A which heats the laser gas and the manifold 4A while the laser gas from the other branch is fed to the other laser tube 2 through a connection tube 8B, a heat exchanger 9B which heats the laser gas and the manifold 4b. Each of the connection tubes 8A, 8B is manufactured from a insulating material, and is cylindrical in configuration. One of the manifolds, 4B, is provided with a reflecting mirror 10 which reflects the laser radiation excited within the associated laser tube 2 while the other manifold 4A is provided with an output mirror 11 which reflects laser radiation excited within the associated laser tube 2 and also transmits the laser radiation therethrough. The reflecting mirror 10 and the output mirror 11 are disposed in opposing relationship with each other on the axis of the pair of laser tubes 2. Laser radiation which is driven into resonance between the pair of mirrors 10, 11 can be emitted to the left through the output mirror 11. Each of the laser tubes 2 contains two sets of main electrodes disposed in opposing relationship with each other, each set comprising a pair of main electrodes 12, 13. One of the main electrodes in each pair comprises a ground electrode 12, which is disposed toward either end of each laser tube 2, or adjacent to the respective manifolds 3, 4A, 4B. The other or non-grounded electrode is disposed at the center of each laser tube. In the present embodiment, the ground electrode 12 is used as an anode while the non-grounded electrode 13 is used as a cathode. Alternatively, the ground electrode 12 may be used as a cathode and the non-grounded electrode 13 may be used as an anode. The electrodes 12, 13 of the respective pairs are connected through leads 14 to a d.c. high voltage circuit 15 which functions as a power source to apply a high voltage across the electrodes 12, 13 of each pair while passing a laser gas through the laser tube 2, thus producing a discharge across the pair of main electrodes to enable the laser gas to be excited. Fig.2 is an enlarged cross section of the left-hand laser tube 2. The laser tube 2 has a wall thickness which is uniform throughout the axial length thereof. However, the laser tube has a portion 2a of an increased diameter at its opposite axial ends and at its central portion while it has a portion 2b of a reduced diameter in the remainder. The portion 2b of a reduced diameter and the portion 2a of an increased diameter are jointed together by a tapered portion 2c. As mentioned previously, the ground electrode 12 (anode) is disposed in the potions 2a of the laser tube which are disposed at the opposite ends while the non-grounded electrode 13 (cathode) is disposed in the portion 2a of an increased diameter which is disposed at the center of the laser tube 2. The portion 2a of the laser tube 2 which has an increased diameter is provided with a plurality of protuberances 2d which extend radially outward. Either the ground electrode 12 (anode) or the non-grounded electrode 13 (cathode) in the form of a rod radially extends through the center of each protuberance 2d and is secured in place by an intermediate glass member. The purpose of the intermediate glass member is to accommodate for thermal expansion which the respective electrodes 12, 13 experience. As shown in Figs.3, 5 and 7, six protuberances 2d are provided which are spaced apart at an equal interval circumferentially of the laser tube 2, each protuberance 2d containing either the ground electrode 12 (anode) or non-grounded electrode 13 (cathode). Thus, in the present embodiment, each of the ground electrode 12 (anode) and the non-grounded electrode 13 (cathode) comprises a set of six rods which are spaced apart circumferentially. As shown in Fig.6, the non-grounded electrode 13 (cathode) which is disposed in the portion 2a of an increased diameter which is located at the center of the laser tube 2 is generally L-shaped. Specifically, the electrode 13 comprises a connection piece 13a which is connected to the protuberance 2b of the laser tube 2 and supported to extend along the radial direction of the laser tube 2, and a distal end 13b which continues from the inner end of the connection piece 13a and is bent at right angles therefrom. The electrode 13 thus constructed has its distal end 13b directed toward the ground electrode 12 (anode). Thus, referring to Fig.2, the right-hand electrode 13 (cathode) has its distal end 13b directed downstream as viewed in the direction of the flow of laser gas. Conversely, the left-hand non-grounded electrode 13 (cathode) has its distal end 13b directed toward the left-hand ground electrode 12 (anode), or upstream as viewed in the direction of flow of the laser gas. In addition, as indicated in Fig.5, the distal end 13b of the electrode 13 (cathode) lies substantially on the same plane as the inner peripheral surface of the portion 2b of a reduced diameter, as viewed in the radial direction of the laser tube 2. By contrast, the ground electrode 12 (anode) which is located on the upstream side (or to the left) as viewed in the direction of flow of the laser gas comprises a rectilinear rod, as indicated in Figs.7 and 8. The inner end of the ground electrode 12 or its distal end lies substantially on the same plane as the inner peripheral surface of the portion 2b of a reduced diameter, as viewed in the radial direction of the laser tube 2. In the present embodiment, in order to improve the efficiency of exciting the laser radiation, the ground electrode 12 which is disposed downstream (or to the right) as viewed in the direction of flow laser gas is modified in a manner to be described below. Thus, referring to Figs.3 and 4, the ground electrode 12 which is disposed downstream is generally substantially L-shaped. The ground electrode 12 comprises a connection piece 12a connected to the protuberance 2d of the tube 2 and extending radially of the laser tube 2, and a distal end 12b which continues from the inner end of the connection piece 12a and is bent therefrom at an obtuse angle. In the present embodiment, the distal end 12b of the downstream ground electrode 12 thus constructed is supported to extend in a direction intersecting with the axial direction of the laser tube 2, as shown in Fig.4. In addition, the distal end 12b of the ground electrode 12 which is supported in this manner has its end located to be slightly displaced radially outward from the inner peripheral surface of the portion 2b of the laser tube 2 which has a reduced diameter. In this manner, the distal end 12b of the ground electrode 12 extends in a direction of tangent to the inner peripheral surface of the portion 2b of a reduced diameter, and all the distal ends are directed in a similar orientation. Preferably, the connection piece 12a and the distal end 12b of the ground electrode 12 form an angle of approximately 120 therebetween. It is to be understood that the right-hand laser tube 2 shown in Fig.1 has the identical construction as the left-hand laser tube 2, mentioned above, as referenced to the direction of flow of the laser gas, and therefore will not to be described. As described, in the present embodiment, the ground electrode 12 (anode) which is disposed downstream as viewed in the direction of flow of the laser gas is substantially L-shaped, and its distal end 12b is disposed to intersect with the direction of flow of the laser gas. This is effective in improving the oscillation efficiency when exciting the laser radiation. Fig.9 graphically indicates a result of experiment which compared the present embodiment against the prior art with respect to the oscillation efficiency in exciting the laser radiation. It will be appreciated from Fig.9 that the oscillation efficiency in exciting the laser radiation according to the embodiment is improved over the prior art. The prior art which is relied upon in this experiment is a laser oscillator disclosed in Japanese Laid-Open Patent Application No.291, 391/94. In this laser oscillator of the prior art, not only the central electrode 13, but the ground electrode 12 is also L-shaped in the same manner as the non-grounded electrode 13, with the distal ends of the both L-shape electrodes 12, 13 disposed in opposing relationship with each other within the laser tube 2. Fig. 10 shows a modification of the above-detailed embodiment in a simplified form. While the two pairs of main electrodes 12, 13 are disposed within a single laser tube 2 in the first embodiment mentioned above, only one pair of main electrodes 112, 113 are disposed in the second embodiment. Specifically, an L-shaped main electrode 113, which serves as an anode, is disposed at an upstream position, as viewed in the direction of flow of the laser gas, with its distal end 113b supported to extend downstream. By contrast, an main electrode 112 which is disposed downstream as viewed in the direction of flow of the laser gas serves as a cathode, and is constructed in the same manner as in the first embodiment, with its distal end 112b supported to intersect with the axial direction of the laser tube 2 in the same manner as in the first embodiment. The second embodiment thus constructed achieves a similar function and effect as achieved by the first embodiment. In the second embodiment, parts corresponding to those shown in the first embodiment are designated by like numerals and characters as used before, to which 100 is added. As an alternative, only the right-hand half, located to the right of the axial center of the laser tube 2 shown in Fig.2 may comprise a laser tube 2. With this arrangement, a similar function and effect can be achieved as achieved by the described embodiments. Fig. 11 shows an embodiment according to the invention which is based on the construction of the laser tube according to the embodiment shown in Fig.2, and to which preliminary ionization electrodes are added. Thus, referring to Fig.11, a pair of ring-shaped preliminary ionization electrodes 221 are disposed around the outer periphery of a laser tube 202 at a location which is upstream of a most upstream (or leftmost) main electrode 212, as viewed in the direction of flow of a laser gas. As shown to an enlarged scale in Fig.12, each of the preliminary ionization electrodes 221 comprises a thin sheet of copper. The pair of preliminary ionization electrode 221 are mounted around the outer peripheral surface of the laser tube 202 so that an equal distance or a spacing L can be maintained therebetween, as viewed in the axial direction of the laser tube 202, over the entire circumferential range of the laser tube 202. The both preliminary ionization electrodes 221 are connected to a devoted a.c. high voltage source 222. Immediately before a main discharge takes place across the main electrodes 212, 213, an a.c. voltage of 3,000V is applied from the source 222 across the both the preliminary ionization electrodes 221, thus producing a preliminary ionization within the laser tube 202 at a location of the both electrodes 221. This allows a subsequent main discharge to occur smoothly. In the embodiment thus constructed, the pair of ring-shaped preliminary ionization electrodes 221 are provided separately from the main electrodes 212, 213 and are connected to the devoted a.c. source 222. Accordingly, an even preliminary ionization can occur within the laser tube 202 independently from the diameter of the laser tube 202. This allows a smooth and stabilized main discharge to occur between the main electrodes 212, 213. Because the pair of preliminary ionization electrodes 221 are spaced apart at an equal spacing over the entire circumferential range thereof, it is possible to produce an even preliminary ionization over the entire circumferential range thereof. Accordingly, in this embodiment, the oscillation efficiency in exciting the laser radiation can be improved over the embodiments shown in Figs. 1 to 10. In this embodiment, a downstream ground electrode (anode), as viewed in the direction of flow of laser gas, is substantially L-shaped, with its distal end disposed in a direction transverse to the direction of flow of laser gas in the similar manner as in the embodiments of Figs. 1 to 10. However, where a pre-ionization electrode is provided, the distal end of the downstream L-shaped ground electrode (anode) may be directed toward the upstream electrode. Figs.13 and 14 show another embodiment of the invention in which preliminary ionization electrodes are provided. In this embodiment, each of the preliminary ionization electrodes 321 comprises a copper wire which is circular in section. In this embodiment, a pair of annular grooves 302e, which are spaced apart by a given axial distance, are formed in the outer peripheral surface of a laser tube 302 for receiving the preliminary ionization electrodes 321 comprising the copper wires therein. As a result of forming the annular grooves 302e in the outer peripheral surface of the laser tube 302, annular projections 302e are formed in the inner peripheral surface of the laser tube 302 at corresponding positions in this embodiment. This embodiment again achieves a similar function and effect as achieved by the fourth embodiment. Fig.15 shows an embodiment of the invention in which the annular projections 302e formed in the laser tube 302 of Figs.13 and 14 are eliminated to provide a smooth inner peripheral surface for a laser tube 402. In other respects, the arrangement is similar to the embodiment of Figs.13 and 14, and achieves a similar function and effect. In the embodiments of the invention, an a.c. high voltage source is used as a power source for the preliminary ionization electrodes. However, the a.c. source may be replaced by a power source which produces a pulse wave of a high voltage to be applied across the preliminary ionization electrodes.

Claims: A laser oscillator having at least one laser tube (202) comprising at least one pair of main electrodes (212,213) disposed within the laser tube, a d.c. power source which applies a high voltage across the main electrodes, and gas feed means which feeds a gas into the laser tube (202) and maintains a gas flow through the laser tube; wherein a pair of ring-shaped preliminary ionization electrodes (221) are disposed upstream of the main electrodes (212,213) as viewed in the direction of the gas flow which passes through the laser tube (202); a preliminary ionization power source (222) being provided for applying a pulse wave of high voltage or an a.c. of high voltage across the preliminary ionization electrodes (221). A laser oscillator according to claim 1 in which the pair of preliminary ionization electrodes (221) are disposed around the outer peripheral surface of the laser tube (202) while maintaining a given spacing therebetween in the axial direction of the laser tube (202). A laser oscillator according to claim 1 or 2 in which the pair of preliminary ionization electrodes (321) are disposed in a pair of annular grooves (302e) which are formed in the outer periphery of the laser tube (302) with an axial separation therebetween. A laser oscillator according to claim 1 in which one (13) of the main electrodes of the pair which is disposed downstream as viewed in the direction of the gas flow is substantially L-shaped, with a distal end (13b) of the main electrode being supported to extend in a direction to intersect with the direction of the gas flow. A laser oscillator according to claim 4 in which two pairs of main electrodes (12,13) are sequentially disposed within the laser tube in the axial direction thereof, a most downstream one of the main electrodes of the two pairs, as viewed in the direction of the gas flow, being L-shaped.

Inventors: KOSEKI RYOJI, MURAYAMA KATSUKI, KOSEKI, RYOJI, MURAYAMA, KATSUKI, KOSEKI, RYOJI, C/O SHIBUYA KOGYO CO., LTD.,, MURAYAMA, KATSUKI, C/O SHIBUYA KOGYO CO., LTD.,
Applicants: SHIBUYA KOGYO CO LTD, SHIBUYA KOGYO CO., LTD
Application year: 1997
Main classification: H01S3
IPC codes: H01S3