LASER OSCILLATING DEVICE

Abstract: A support unit (20a) for supporting an OPM holder (15a) so as to be vertical to the laser beam axis is disposed in the lower part of the OPM holder (15a). A rotary shaft (19) is inserted into the support unit (20a) and rotary shaft support unit (20b), and the OPM holder (15a) and DT base (17) are assembled together. Thus, a rotation support unit (200) is composed. The rotation support unit has a degree of freedom in the rotating direction of arrow (202). On the other hand, in the lower part of an RM holder (15b), a support bar (21) is provided. At the DT base (17), a rotating element (22) and a rotating element support unit (23) supporting the rotating element are composed so as to support the support bar. Thus, a slider structure (220) slidable in the optical axis direction is formed. The slider structure has a degree of freedom in the direction of arrow (222).

Description: TECHNICAL FIELD The present invention relates to a laser oscillator, and more particularly to an axial flow type gas laser oscillator having a discharge tube disposed in the optical axis direction. BACKGROUND ART Fig. 8 shows an example of a schematic configuration of a so called axial flow type gas laser oscillator. Referring to Fig. 8, the axial flow gas laser oscillator (hereinafter called AFGLO) is explained. As shown in Fig. 8, the AFGLO is mainly composed of a laser resonator, a power supply unit 4, and a laser gas circulation part. The laser resonator is composed of a discharge tube 1 having a discharge space 5, a rear mirror (hereinafter called RM) 6, and an output mirror (hereinafter called OPM) 7. The discharge tube (hereinafter called DT) 1 is composed of glass or other dielectric materials, and electrodes 2, 3 are disposed near both ends of the DT 1. In the DT 1 between the electrodes 2 and 3 the discharge space (hereinafter called DA) 5 is placed. The RM 6 and OPM 7 are disposed to enclose a plurality of DAs 5. The RM 6 is a reflector having a reflectivity of nearly 100%. The OPM 7 is a partial reflector, and a laser beam 8 is emitted from the OPM 7. The power supply unit 4 is connected to the electrodes 2, 3 to perform a discharge in the DA 5. The laser gas circulation part (hereinafter called LGCP) is composed of a blower 13, heat exchangers 11, 12, a laser gas passage 10, and a plurality of DAs 5 in DTs 1. The laser gas circulates in the LGCP composing the AFGLO in a direction of arrow 9. The blower 13 is for circulating the laser gas. By this blower 13, the flow velocity of laser gas is set at about 100 m/sec in the DA 5. The pressure in the LGCP is about 100 to 200 Torr. When a specified voltage is applied to the electrodes 2, 3 from the power supply unit 4, the DA 5 discharges. By this discharge and operation of the blower, the temperature of the laser gas elevates. The heat exchangers 11 and 12 are provided to cool the laser gas raised in temperature. Described above is the configuration of the conventional AFGLO, and its operation is explained below. The laser gas sent out from the blower 13 is guided into the DT 1 through the laser gas passage 10. In this state, when a specified voltage is applied to the electrodes 2, 3 from the power supply unit 4, the DA 5 discharges. The laser gas in the DA 5 obtains this discharge energy and is excited. The excited laser gas becomes a resonant state in the laser resonator formed of the RM 6 and OPM 7. As a result, a laser beam 8 is emitted from the OPM 7. The output laser beam 8 is used for laser machining or other application. Problems of the conventional AFGLO are described below. A first problem is described. Fig. 9 shows a schematic configuration of the laser resonator including an optical bench of conventional AFGLO. The OPM 7 is held by an output mirror holder 150a. The RM 6 is held by a rear mirror holder 150b. On the other hand, the DT 1 is held by a discharge tube holder base (hereinafter called DT base) 170 which is an optical bench, by way of a discharge tube holder (hereinafter called DT holder) 160. Both ends of the DT base 170 are connected to corresponding mirror holders 150a, 150b. The mirror holders 150a, 150b, and DT base 170 are assembled to be in an unitary structure. The DT holder 160 and mirror holders 150a, 150b are connected through a connection tube 180 with both ends held with O-rings or the like so as to be slidable. In this configuration, the axis linking the center of the RM 6 and the center of the OPM 7, and axes of the RM 6 and OPM 7 are disposed to be perpendicular to each other. That is, the RM 6 and OPM 7 are disposed parallel to each other. The parallelism is adjusted to a precision of several µm or less to each other. The axis linking the centers of the RM 6 and OPM 7 is disposed to coincide with the central axis of the DT 1. To obtain a normal laser output,following conditions are required; the parallelism of RM 6 and OPM 7 of 10 -6 radian or less, and the precision of the axis formed by the mirror and the axis formed by the DT is tens of µm or less. To maintain this precision, the mirror holders and the DT base are formed in an unitary rigid structure. In the conventional laser oscillator having such configuration, the first problem is explained. The degree of vacuum in LGCP is about 100 to 200 Torr. On the other hand, its outside is an atmospheric pressure (760 Torr). Between the inside and outside of the LGCP, a stress due to the pressure difference (hereafter called vacuum force) is applied. Usually, both ends of the DT base 170 are held by a support structure (not shown). The LGCP is also held by a support structure (not shown). Therefore, in the DT holder 160 in the central part shown in Fig. 8, a downward stress is applied due to the pressure difference. The DT base 170 is made of material of high rigidity such as steel so as not to be bent by the stress due to such pressure difference. To maintain the rigidity, the DT base 170 has a considerably large structure as compared with other parts such as DT 1. For the purpose of increasing the rigidity, however, the size is limited. Therefore, by the vacuum force, the DT base 170 may be bent by about tens of µm. As described above, the DT base 170 and mirror holders 150a, 150b are assembled in an unitary structure. Accordingly, if the DT base 170 is bent only by tens of µm, the parallelism between the mirror holder 150a and mirror holder 150b is changed. By this change in parallelism, the laser output may be lowered. Besides, since the thermal capacity of the DT base 170 is large, if ambient temperature varies, it cannot follow up the temperature changes. Due to change in ambient temperature, a temperature difference may occur in the parts of the DT base 170 (for example, temperature difference between upper part and lower part, or temperature difference between right side and left side, as shown in Fig. 9). If a temperature difference occurs, the DT base 170 is bent due to a thermal expansion or a thermal shrinkage. As a result, the parallelism of RM 6 and OPM 7 cannot be maintained. By this change in parallelism, the laser output may be lowered. Fig. 10 schematically shows the change in the laser output depending on the ambient temperature. To address this problem, hitherto, the following measures were taken. As a measure against bending of DT base 170 by vacuum force, for example, it was attempted to user a canceler for canceling the stress due to pressure difference in order to keep balance of stress due to pressure difference between inside and outside. However, the canceler generated an unexpected stress, and produced adverse effects. On the other hand, as a measure against the expansion and the shrinkage due to the temperature difference, it was attempted to control the DT base 170 at a constant temperature. This attempt is intended to pass liquid (for example, water) in the DT base 170, and control the liquid temperature constant. However, the volume of the DT base 170 is large in order increase the rigidity. Therefore, the thermal capacity of the DT base 170 becomes larger, and the temperature difference cannot be eliminated completely. Document JP 02 021 678 discloses an axial-flow type gas laser with a resonator mirror support structure comprising a set of rods connecting the two resonator mirror holders to each other. Document JP 02 168 683 discloses a gas laser oscillator in which the mirror holders are connected by rods and are provided with fixing parts for fixing the holders to the support base. The first fixing part has a rotational degree of freedom and the second fixing part is slidable along the laser axial direction. A second problem of the conventional AFGLO is as follows. The flow of laser gas in the DT 1 is preferred to be uniform in the gas flow direction as far as possible from entry of gas in the DT 1 until its exhaust. When the gas flow is uniform, the discharge state is stable. As a result, the efficiency of laser output versus an electric input to the DA 5 is enhanced (known as a laser oscillation efficiency). Owing to the specific configuration of the AFGLO, the structure is complicated if the laser gas lead-in portion is provided coaxially with the DT 1. Actually, as shown in Fig. 11, the laser gas lead-in portion is generally disposed nearly at right angle to the DT 1. Fig. 11 and Fig. 12 schematically show the gas flow in the DT 1. Fig. 12 is a sectional view along line 29-29 in Fig. 11. In this configuration, as shown in Fig. 11, in the DT 1, particularly near the laser gas inlet 137, a vortex 136 is likely to occur in the gas flow. By the vortex , the gas flow in the DT is disturbed. As a result, the laser oscillation efficiency cannot be enhanced. Fig. 13 shows the relation between electric input in the DA 5 and laser output. As proposed in a prior art (Japanese Patent Laid-Open Publication No. 7-142787), a chamber is provided for storing the gas temporarily, and it is connected to the laser gas lead-in portion. By eliminating the directivity of laser gas entering the laser gas lead-in portion, it is intended to eliminate a non-uniformity of gas flow in the DT. According to the study by the present inventors, the gas flow becomes not uniform when feeding gas is led into the DT from the laser lead-in portion, and vortices were formed in various portions. As a result, the laser oscillation efficiency could not be further enhanced by the configuration proposed in Japanese Patent Laid-open Publication No. 7-142787. Further, the conventional AFGLO has a third problem. When the voltage between the electrodes 2, 3 provided around the DT 1 reaches a discharge start voltage, discharge starts. At this discharge start moment, a large rush current flows into the DT 1. When discharge current starts to flow, the impedance of DT drops, and soon at maintenance voltage of about 20 kV settles. In this state, the current is stable and a uniform discharge is obtained. However, due to rush current at the discharge start moment, the discharge is disturbed temporarily. It takes a certain time until the discharge is stabilized. The value of the rush current is proportional to the discharge start voltage. It is hence important to lower the discharge start voltage in order to stabilize discharge. In a prior art, as shown in Fig. 14, an auxiliary electrode 156 is disposed near the electrode 2 in the DT 1, and the auxiliary electrode 156 and the electrode 3 are connected with a high resistance resistor 158 of several MΩ. In this case, since the distance between the auxiliary electrode 156 and electrode 3 is too long, if laser gas is ionized between the auxiliary electrode 156 and electrode 2, it is almost recombined before reaching the electrode 3. Therefore, in this configuration, notable effect for decreasing the discharge start voltage cannot be obtained. Fig. 15 shows another typical example of prior art. Along the outer surface of the DT 1, a conductor 159 is extended from the electrode 2 to the electrode 3 side, and an auxiliary electrode 156 is attached to the end of the conductor 159 closer to the electrode 3 side. The auxiliary electrode 156 is attached to the outer surface of the DT 1 via an insulating sheet 162 made of a dielectric material. To lower the discharge start voltage, it was attempted to reduce the thickness of the dielectric materials, but holes were formed in the wall of the DT 1 due to micro discharge in a course of time. Thus, in the conventional AFGLO, usually, a mechanism called auxiliary electrode was added. It is an attempt to lower the rush current upon start of discharge by lowering the insulation breakdown voltage in the DT by some mechanism so as to ignite discharge easily. The auxiliary electrode itself was a good idea, but none of the prior arts was satisfactory in the aspects of performance and reliability. Summing up, in the conventional AFGLO, 1) Stress occurs in the parts of the resonator due to pressure difference between the LGCP and the outside at atmospheric pressure. By this stress, the DT base 170 may be bent by about tens of µm. Since the DT base 170 and a pair of mirror holders 150 are in unitary structure, if the DT base 170 is bent only by tens of µm, the mutual angle of the pair of mirror holders 150a and 150b is varied. As a result, it was difficult to enhance the stability of laser output further. 2) In the DT, the laser gas flow tends to be not uniform in the central part or in peripheral part of the DT. As a result, uniform gas flow is not realized. Hence, the energy efficiency could not be enhanced further. 3) A large rush current flows in the DT at the discharge start moment when the voltage between the electrodes 2, 3 reaches the discharge start voltage. When the rush current flows at the discharge start moment, a large current flows, and the discharge is disturbed temporarily. Accordingly, it takes some time until discharge is stabilized, and discharge is unstable in this period (that is, the laser output is unstable). This transient unstable period of discharge cannot be shortened. DISCLOSURE OF THE INVENTION The present invention is made to improve the above first problem. To address the first problem, the AFGLO of the invention comprises: a) a DT for exciting laser medium disposed inside by applying energy; b) at least a pair of mirrors disposed on an optical axis of laser beam emitted from the laser medium excited by the DT; c) at least a pair of mirror holders for holding the mirrors; d) a plurality of mirror holder connecting rods for connecting the mirror holders; e) a DT holder for holding the DT; and f) a DT base for holding the DT holder, wherein, g) one mirror holder is fixed to the DT base in the laser beam axial direction and in the orthogonal direction to the laser beam axis, h) the mirror holder has a degree of freedom in the rotating direction within the plane including the laser beam axial direction, and i) the other mirror holder is fixed to the DT base in the vertical direction to the laser beam axis, and is slidable in the laser beam axial direction. j) a plurality of ribs connect a plurality of mirror holder connecting members with the discharge tube support, said ribs being slidable in a direction perpendicular to the laser beam axis. To address the second problem, an AFGLO can comprise: a) a DT for passing laser gas inside and exciting the laser gas; b) electrodes disposed near both ends of the DT; c) at least one of the electrodes being disposed near the laser gas inlet of the DT; and d) a laser gas passage for supplying laser gas to the DT, wherein, e) the configuration suffices the following relation, 1.1 A < B < 1.7A where A is the inner diameter of the DT, B is the width in the gas flow direction of the laser gas passage near the laser gas inlet of the DT and in the vertical direction to the gas flow direction in the DT. To addres the third problem, an AFGLO can comprise: a) a DT; b) electrodes disposed near both ends of the DT; and c) a high voltage power supply for applying a high voltage between the electrodes, wherein, d) a hole is opened in the DT, e) an auxiliary electrode is disposed in the hole, f) the auxiliary electrode is connected to one of the electrodes via a high resistance resistor, g) the position of the hole opened in the DT is at a distance of 0.4L to 0.7L from the electrode not connected to the auxiliary electrode where L is the distance between the two electrodes, and h) the resistance of the high resistance resistor is in a range of 1 MΩ or more and 100 MΩ or less. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a schematic configuration of an exemplary axial flow gas laser oscillator. Fig. 2 shows a configuration of resonator section of the laser oscillator shown in Fig. 1. Fig. 3A is a left side view of the resonator section shown in Fig. 2. Fig. 3B is a right side view of the resonator section shown in Fig. 2. Fig. 4 is a three-side view showing a coupling area of OPM holder and DT base of laser oscillator of other configuration of example 1. Fig. 5A is a detailed view of an optical bench of a laser oscillator conf iguration of the present invention. Fig. 5B is an enlarged sectional view of a stand near cushioning ball structure shown in Fig. 5A. Fig. 6 is a view of RM 6 seen from 6-6 plane shown in Fig. 5A. Fig. 7 shows difference in laser output due to change in ambient temperature between an example of the present invention and a prior art. Fig. 8 shows a schematic configuration of conventional axial flow gas laser oscillator. Fig. 9 is a schematic view of optical bench section of the conventional laser oscillator. Fig. 10 shows output stability in the conventional laser oscillator. Fig. 11 is a schematic diagram showing detail of DT section in the configuration of the conventional laser oscillator and laser gas flow. Fig. 12 is a schematic diagram showing laser gas flow in 29-29 plane shown in Fig. 11. Fig. 13 is a diagram showing the relation between electric input and laser output in prior art. Fig. 14 is a schematic diagram showing configuration of DT section in prior art. Fig. 15 is a schematic diagram showing configuration of other DT section in prior art. Fig. 16 is a diagram showing the relation between electric input and laser output in prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Embodiments of the invention are described below with referrence to the accompanying drawings. Fig. 1 shows an examplary laser oscillator. Fig. 2 shows a configuration of resonator section of the laser oscillator shown in Fig. 1. Fig. 3A is a left side view of the resonator section shown in Fig. 2. Fig. 3B is a right side view of the resonator section shown in Fig. 2. Same parts as in the conventional laser oscillator shown in Fig. 8 are identified with same reference numerals, and their description is omitted. The exemplary laser oscillator is explained by referring to Fig. 1, Fig. 2, Fig. 3A, and Fig. 3B. An OPM holder 15a and an RM holder 15b are supported to be parallel to each other by a plurality of mirror holder connecting rods (hereinafter called MHCR) 14. A rotation support unit 200 is configured to support the OPM holder 15a on a DT base 17. A support unit 20a for supporting the OPM holder 15a to be perpendicular to the laser beam axis is disposed in the lower part of the OPM holder 15a. A rotary shaft support unit 20b is disposed on the DT base 17. A hole for inserting a rotary shaft 19 is opened in the support unit 20a and rotary shaft support unit 20b. The rotary shaft 19 is inserted into the support unit 20a and rotary shaft support unit 20b, so that the OPM holder 15a and DT base 17 are assembled together. The contact portions of the rotary shaft 19 and rotary shaft support units 20a, 20b are finished to a smooth surface so as to rotate smoothly with minimum friction. Or a component extremely small in friction against rotation such as ball bearing (or roller bearing) is inserted. Thus, the rotary shaft 19, support unit 20a, and rotary shaft support unit 29b are combined to compose the rotation support unit 200 for supporting the OPM holder 15a on the DT base 17. The rotation support unit 200 has a degree of freedom in the rotating direction shown by an arrow 202 shown in Fig. 1 and Fig. 2. On the other hand, a support bar 21 is provided in the lower part of the RM holder 15b. At the DT base 17 side, a rotating element 22 and a rotating element support unit 23 for supporting the rotating element 22 are disposed for supporting the support bar 21. In this manner, a slider structure 220 slidable in the optical axis direction is formed. This slider structure 220 has a degree of freedom in the optical axis direction shown by an arrow 302 in Fig. 1 and Fig. 2. In this configuration, the OPM holder 15a and DT base 17 are fixed in the orthogonal direction to the laser beam axial direction. However, the OPM holder 15a and DT base 17 have a degree of freedom only in the rotating direction within the plane including the laser beam axial direction. As a result, the OPM side mirror holder 15a and DT base 17 can be coupled without deviation of optical axis. On the other hand, the rear mirror holder 15b and DT base 17 are fixed in the orthogonal direction to the laser beam axial direction (however, they are free in the upward direction, strictly). That is, by a weight (own weight) of the mirror holder 15b, the rear mirror holder 15b and DT base 17 are supposed to be fixed. Of course, this configuration is free in the sliding direction of optical axis direction and in the rotating direction within the plane including the optical axis direction. As a result, the RM side mirror holder and DT support unit are also coupled without deviation of optical axis same as at the OPM side. Following explanation is made when the DT base 17 is deformed by the vacuum force or the temperature change. When the DT base 17 is bent by vacuum force, rotation within the plane including the optical axis direction occurs in the coupling portion of the mirror holder and DT support unit. As described above, this portion is free in the rotating direction both at the OPM side and RM side. Accordingly, the mirror holder is free from any force causing change in the parallelism due to vacuum force or thermal stress. In the event of thermal expansion or thermal shrinkage of DT support unit, linear displacement in the optical axis direction occurs at the coupling portion with the mirror holder, but since the RM holder is held free in this direction, force to cause change in parallelism is not applied to the mirror holder by the vacuum force or the thermal stress. An excellent feature of the configuration of the laser oscillator lies in the coupling portion of the OPM holder and DT support unit. This system also has a degree of freedom structurally other than the rotating direction within the plane including the optical axis direction. For example, it may be configured to have coupling member high in degree of freedom such as cushioning balls at two positions each in the lower part of the OPM holder 15a and RM holder 15b. In this system, however, the degree of freedom is limited by fixing at two points. Accordingly, it is likely to cause change in the parallelism due to vacuum force. Besides, the distance between two fixing points varies due to thermal expansion or thermal shrinkage of the mirror holder itself, and hence a force to cause change in parallelism is likely to occur. Fig. 4 shows detailed views of junction of OPM holder and DT support unit of a laser oscillator. The rotary shaft 19, support unit 20a, and rotary shaft support unit 20b are combined without clearance (without gap). However, if completely free from gap, rotation is not smooth due to friction. As mentioned above, by inserting a ball bearing in the contact portions of the rotary shaft 19, support unit 20a, and rotary shaft support unit 20b, it is substantially free from clearance to the parallel direction to the optical axis direction. Besides, as being pushed down by the own weight of the mirror holder, the central axis of the discharge tube and optical axes of the mirrors, and a relative position between the mirrors are hardly changed and are stable. However, concerning the direction perpendicular to the optical axis, a gap is needed for smooth rotation between the support unit 20a and rotary shaft support unit 20b. To prevent looseness due to this gap, an elastic force is employed to push the upper rotary shaft support unit 20a to the lower rotary shaft support unit 20b at one side. Fig. 4 shows an example of such structure. For example, two spring members 24 are symmetrically disposed on both sides of the rotary shaft, and the elastic force of the spring members 24 is applied to the support unit 20a. Between a spring holder 25 provided on the rotary shaft 19 and the upper rotary shaft member 20a, the spring members 24 are placed shrinked. Besides, in order that the spring holder 25 and spring members 24 may not impede the motion in the rotating direction, a rotating element such as cushioning ball 26 is inserted in the junction between the rotary shaft 19 and spring holder 25. However, as for linkage of RM holder 15b and DT base 17, it is not limitted to one-point fixing as described above in the present laser configuration. The RM holder and DT support unit may be fixed at two points by using cushioning balls or other coupling members having high degree of freedom. At this time, there is no problem if the OPM side is fixed at one point as shown in the embodiment of the present invention. Fig. 5 is a detailed view of an optical bench of laser oscillator showing an embodiment of the invention. Same as in the example shown in Fig. 2, the mirror holders 15a and 15b are mutually coupled by means of a plurality of MHCRs 14. Similarly, the OPM holder 15a is supported on the DT base 17 by means of the rotation support unit 200. On the other hand, in the lower part of the RM holder 15b, cushioning balls 26 are disposed at two points in the horizontal direction. The rear mirror holder 15b is coupled to the DT base 17 through the pillow balls 26. Fig. 6 is a view of RM 6 seen in a direction from 6-6 shown in Fig. 5. As shown in Fig. 6, for connecting the DT holder 16, DT base 17, and MHCRs 14, ribs 27 are disposed at four positions. The ribs 27 are disposed near the center of MHCRs 14. The ribs 27 and MHCRs 14 are designed to slide slightly in the direction orthogonal to the plane of the drawing. The optical bench stabilizing effect by inserting the ribs 27 is explained. When the DT base 17 id deformed by vacuum force or temperature change, in particular, when expanded or shrinked by temperature change, the following effects occur. At this time, in the coupling portion of the mirror holder and DT base 17, a linear displacement occurs in the optical axis direction. However, the pillow balls are free to move because sliding occurs between the pillow balls and the shaft passing through the pillow balls. Accordingly, the RM holder is free in this direction. Therefore, any force causing change in parallelism does not occur on the mirror holder due to thermal stress. However, even if a friction is reduced so as to be freely movable structurally, actually, the friction is not zero. The junction of the rear mirror holder 15b and DT base 17 is pushed in the direction of gravity (that is, in the downward direction in Fig. 5) due to the own weight of the rear mirror holder 15b. Therefore, a frictional force occurs in this portion, strictly speaking. On the MHCR 14, too, a tensile or compressive force works in the optical axis direction. The MHCR 14 is a circular column of about 50 mm in diameter, and 1000 to 2000 mm in length. When tensile or compressive force works in the optical axis direction (that is, in the longitudinal direction of MHCR 14), the MHCR 14 deflects. At this time, if ribs 27 are not disposed, each MHCR 14 is bent in an arbitrary direction. As a result, the parallelism of the OPM holder 15a and RM holder 15b is broken. When four MHCRs 14 and ribs 27 for coupling the DT holder 16 and DT base 17 are disposed, the rigidity of the MHCRs 14 is enhanced, and they are not bent by frictional force. Therefore, the parallelism of the mutual mirror holders is maintained. Further, when all MHCRs 14 are made to deflect in the central direction or in the peripheral direction, the parallelism of the OPM holder 15a and RM holder 15b is maintained more accurately. For example, four MHCRs 14 are mutually attracted in the central direction by several millimeters by the ribs 27. The mirror holder connecting members are attracted in the central direction by about several millimeters by the ribs 27, and are slightly warped. In this state, when a tensile or compressive force is applied to the MHCRs 14, all of four MHCRs 14 are deflected in the central direction. As a result, the parallelism of the OPM holder 15a and RM holder 15b is maintained. On the contrary, same effects are obtained by warping the four MHCRs 14 in mutually opposite directions by the ribs 27. Thus, in the embodiment of the present invention, the optical bench becomes very stable, and the effect of keeping parallelism between mirrors is extremely large. As a result, always stable laser oscillation is possible, and the laser output is substantially stabilized. Fig. 7 shows difference in laser output due to change in ambient temperature between the embodiment of the present invention and a prior art. The axis of abscissa denotes the ambient temperature, and the axis of ordinate represents the laser output. Both in the present embodiment of the invention and in the prior art, it is adjusted so that the mirrors may be parallel to each other at an ambient temperature of 20°C. The diagram shows changes of laser output when the ambient temperature is lowered or raised from this state. As shown in Fig. 7, in the embodiment of the present invention, as compared with the prior art, the laser output is stabilized substantially in spite of the change in ambient temperature. Similar effects are obtained regarding the vacuum force or the external force. The present invention therefore provides a laser oscillator having a stable optical bench, or a stabile mirror parallelism regardless of vacuum force, external force or ambient temperature change, and is capable of obtaining stable laser output all the time. The connecting rods of the mirror holder connecting rods may be composed of pipes. The connecting rods or pipes are preferably made of materials small in coefficient of thermal expansion, so that a small difference in expansion due to temperature difference is effective for the resonator of the present invention. INDUSTRIAL APPLICABILITY The present invention provides a laser oscillator with a stabile optical bench, or a stabilized mirror parallelism, against vacuum force, external force or ambient temperature change, and a stable laser output all the time.

Claims: A laser oscillator comprising: a discharge tube (1) for exciting laser medium disposed inside by applying energy; a first mirror and a second mirror (6,7) disposed on an optical axis of laser beam emitted from the laser medium excited by said discharge tube; a first mirror holder and a second mirror holder (15a,15b) holding said first mirror and second mirror respectively; a plurality of mirror holder connecting members (14) connecting said first mirror holder and second mirror holder; a plurality of discharge tube supports (16) supporting said discharge tube; and first and second fixing parts (202,222) for fixing said first and second mirror holders (15a,15b) to a discharge tube support base (17), characterized in that said first fixing part (202) fixes said first mirror holder (15a) to the discharge tube support base (17) in a laser beam axial direction and in a direction perpendicular to the laser beam axis, said first fixing part having a degree of freedom in a rotating direction within a plane including the laser beam axis; said second fixing part (222) fixes said second mirror holder (15b) to the discharge tube support base (17) in the direction perpendicular to the laser beam axis, said second fixing part being slidable in the laser beam axial direction; and a plurality of ribs (27) connect a plurality of mirror holder connecting members (14) with the discharge tube support (16), said ribs being slidable in a direction perpendicular to the laser beam axis. The laser oscillator of claim 1, wherein said ribs are configured to force the plurality of mirror holder connecting members (14) to deflect to a central direction. The laser oscillator of claim 1, wherein said ribs are configured to force the plurality of mirror holder connecting member (14) to deflect to a peripheral direction. The laser oscillator of claim 1, wherein the first fixing part (202) comprises a rotary shaft member (19) disposed so that a shaft is perpendicular to the laser beam axis, and a rotary shaft support (20a,20b) connecting the rotary shaft member to the mirror holder (15a) and discharge tube support base (17), while keeping a degree of freedom in a rotating direction in a perpendicular plane with respect to the shaft of the rotary shaft member. The laser oscillator of claim 4, wherein an elastic force is applied along the direction of a rotary shaft along the direction of of the fist fixing part (202).

Inventors: HAYASHIKAWA HIROYUKI, HONGU HITOSHI, HAYASHIKAWA, HIROYUKI, HONGU, HITOSHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 2000
Main classification: H01S3
IPC codes: H01S3