Gas laser oscillation device and its optical axis alignment method

Abstract: A gas laser oscillator having two discharge tube columns, both ends of which are connected by a bending unit (18), wherein each column comprises two discharge tubes (1) connected in series. At the opposite ends of the bending unit, one column has a total-reflection mirror (6), and the other column has a partial-reflection mirror (7). These discharge tubes, the bending unit, the total-reflection mirror, and the partial-reflection mirror are mounted to a single optical bench (14). Each end of the discharge tubes is fixed to the optical bench (14) by means of clamp (15a, 15b, 15c, or 16). When counted from the clamp nearest to the partial-reflection mirror, the first clamp (15a), the fourth clamp (15b), and the eighth clamp (15c) are non-movable with respect to the optical bench, while the remaining clamps (16) are movable, and thus adjustable. One total-reflection mirror unit of the two total-reflection mirror units (19 and 20) on the bending unit (18) is non-movable, and the other total-reflection mirror unit is movable.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas laser oscillation device in which the axis of each discharge tube is aligned with the axis of laser. In particular, the present invention relates to a gas laser oscillation device and its optical axis alignment adjustment method, wherein the gas laser oscillation device comprises an optical resonance zone having two or more rows of discharge tubes which are connected at their bending portions by means of a bending unit, with each row made up of one or more discharge tubes which ore connected in series, with a partial-reflection mirror at one end of the optical resonance zone and with a total-reflection mirror at the other end of the optical resonance zone. 2. Description of the Related Art Fig. 8 illustrates the basic configuration of a gas laser oscillation device. Indicated at 1 in Fig. 8 is a discharge tube made of dielectric such as glass and the like. Indicated at 2 and 3 are metallic electrodes disposed inside the discharge tube 1. A high tension power supply 4 is connected to the electrodes 2 and 3. The power supply 4 supplies, for example, a voltage of 30 kV across the electrodes 2 and 3. Indicated at 5 is a discharge space between the electrodes 2 and 3 in the discharge tube 1. A total-reflection mirror is designated 6, and a partial-reflection mirror is designated 7. An optical resonator is formed by the total-reflection mirror 6 disposed on one side of the discharge space 5, and by the partial-reflection mirror 7 disposed on the other side of the discharge space 5. A laser beam 8 is output via the partial-reflection mirror 7. An arrow 9 indicates the direction of gas flow. Laser gas circulates in the axial flow type laser device. A gas feeder pipe is designated 10. Heat exchangers 11 and 12 work to lower the laser gas temperature which rises as a result of discharge action in the discharge space 5 and the operation of a gas blower. The blower 13 is used to circulate the laser gas. The blower 13 causes a gas flow of about 100 m/s to take place in the discharge space 5. The basic structure of the axial flow type gas laser oscillation device has been described above. Described below is how it operates. The high tension power supply 4 supplies a high voltage between a pair of metallic electrodes 2 and 3, resulting in glow discharge in the discharge space 5. The laser gas that passes through the discharge space 5 receives energy from the discharge, and is thus excited. The excited laser gas is put into resonance state in the optical resonator formed by the total-reflection mirror 6 and the partial-reflection mirror 7. The resulting laser beam 8 is output through the partial-reflection mirror 7. The laser beam 8 is then used for welding, cutting, heat treatment, and other applications. Fig. 9 is a detailed view showing a conventional optical resonator portion of a gas laser oscillation device. Mounted on an optical resonator are an optical bench 14, clamps 16 and 17, discharge tubes 1, a bending unit 18, a partial-reflection mirror 7, and a total-reflection mirror 6. All clamps 16 are adjustable. Also mounted on the optical resonator is an adjuster 22 which aligns the optical axis by adjusting two total-reflection mirrors 21 disposed on the bending unit 18. Specifically, a reference optical axis is first set up, and then, all clamps 16 and total-reflection mirrors disposed on the bending unit are adjusted so that the optical axes of all optical elements agree with the reference optical axis. As described later referring to Fig. 5, the clamps 16 are fitted into the optical bench 14 with clearance fit. The clamps 16 are adjustable to within the clearance range which is allowed by clamp mounting screws (not shown) and their holes. The clamps 17 are integrally mounted on the discharge tube 1 as shown in Fig. 3; thus, the clamps 17 are installed along with the discharge tube 1 in order to fit into the clamps 16 after they are adjusted. The description that follows is how the conventional optical axis alignment is adjusted. Indicated at 25 in Fig. 6 and at 26 in Fig. 11 are instruments which are used to visually inspect the position of the optical axis and which, made of translucent material, on their centers, have through holes 27a and 27b, respectively, of 0.5 to 1 mm diameter. Similar to the manner illustrated in Fig. 7, the instrument 25 may be installed onto the clamp 24 on the mounting portion of the partial-reflection mirror 7. Both the accuracy of fit between the instrument 25 and the clamp 24 and the accuracy of fit between the clamp and the optical bench 14 are far better than an optical axis misalignment level normally considered as acceptable. As shown in Fig. 12, the instrument 26 is inserted into a hole (31 in Fig. 10) which is left open with the incidence side total-reflection mirror (28 in Fig. 10) of the bending unit 18 removed. As in the instrument 25, the instrument 26 is inserted into the hole 31 with clearance fit far better than an optical axis misalignment level normally considered acceptable. Under the setup as mentioned above, helium-neon laser beam (hereinafter, simply referred to as laser beam), for example, is directed to the hole 27a at the center of the instrument 25 installed on the clamp 24. The helium-neon laser device is adjusted in positional setting so that the laser beam passes through the hole 27b at the center of the instrument 26. Indicated at 34 both in Fig. 12 and Fig. 13 is laser beam. Since the instruments 25 and 26 are made of translucent material, laser beam causes a light spot on the areas of the instruments, if laser beam fails to meet the holes. That light spot allows the position of the beam axis to be visually located. After making sure that laser beam passes through both the center hole 27a on the instrument 25 installed on the clamp 24 and the center hole 27b on the instrument 26, another instrument 25 is installed onto one clamp 16 between the first instrument 25 and the instrument 26 as shown in Fig. 7. The clamp 16 is then adjusted and secured so that laser beam already set up passes through the center hole 27a of the instrument 16. This step is repeated until all clamps 16 are adjusted. After completing adjustment of all clamps 16, the instrument 26 in Fig. 12 is removed, and then refitted into a next hole (32 in Fig. 10) as shown in Fig. 13. The total-reflection mirror 28 is then adjusted for a proper angle with adjusting screws 22 illustrated in Fig. 9 so that laser beam passes through the center hole 27b on the instrument 26. Indicated at 21 is a total-reflection mirror unit having a total-reflection mirror 28. Next, the instrument 26 is removed from the hole 32, and the instrument 25 is installed onto a clamp 23 (Fig. 9) at the end of the optical resonance zone after the total-reflection mirror 6 is removed. Both the accuracy of fit between the instrument 25 and the clamp 23 and the accuracy of fit between the clamp 23 and the optical bench are for better than an optical axis misalignment level normally considered as acceptable. After the total-reflection mirror 29 is installed on the bending unit 18, the total-reflection mirror 29 is adjusted for a proper angle with an adjusting screw 22 so that laser beam passes through the center hole 27a on the instrument 25. Then, another instrument 25 is installed onto one of clamps 16 arranged between the bending unit 18 and the clamp 23, and that clamp 16 is adjusted and secured so that laser beam passes through the center hole 27a on the instrument 25. Each of the clamps 16 should be adjusted as above. This completes the optical axis alignment adjustment in the entire optical resonance zone. If three discharge tubes or more are connected in series, further adjustment is required accordingly between the bending unit and the total-reflection mirror at the end of the optical resonance zone. In the above-mentioned prior art, the optical axis alignment procedure is complex and requires high standard of adjusting skills, thereby consuming a great deal of time. The machining accuracies of the optical bench and other components have been improved in an attempt to shorten the time required for the optical axis alignment adjustment. Such an attempt has failed in achieving satisfactory results. Higher machining accuracy incurs higher machining cost. Furthermore, even high-accuracy components still result in cumulative errors as a whole, thereby causing the misalignment to occur in the optical axis, even to the extent that the adjustment itself is impossible. SUMMARY OF THE INVENTION Accordingly, an essential object of the present invention is to provide a gas laser oscillation device and its optical axis alignment adjustment method, wherein the machining cost is kept to a minimum, the time required for the optical axis alignment adjustment is substantially reduced, and no particular adjustment skill is required for the adjustment. In accomplishing these and other objects, according to the present invention, there is provided a gas laser oscillation device as defined in Claim 1 and a method of aligning the optical axis of this device as defined in Claim 4. According to the above-mentioned device, by employing a minimum number of clamps which need no adjustment because of their high machining accuracy and by making adjustment-free total-reflection mirror of one side of the bending unit in principle, intermediary clamps may be adjusted with respect to the reference optical axis which is in advance set up on the adjustment-free clamps using laser beam, such as helium-neon laser for adjustment of optical axis. This involves no particular adjustment skill for the optical axis alignment, and substantially shortens the time required for the adjustment. Furthermore, the ratio of high accuracy components to the standard accuracy components is kept low, a rise in the machining cost is kept low as well. The present invention allows criteria for the optical axis alignment adjustment to be clarified and also allows the optical axis alignment to be adjusted without removing the total-reflection mirrors of the bending units. No particular adjustment skills are thus needed, and the time required for the adjustment is substantially reduced. Furthermore, since the number of components which require high machining accuracy standards is kept to a minimum, the total cost involved is lowered. Since the accuracy of the optical axis alignment adjustment depends on the machining accuracy of components, there will be no worry about the adjustment failure because of cumulative machining errors. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features for the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1A is a plan view showing an optical resonator of a gas laser oscillation device according to the present invention; Fig. 1B is a front view showing the optical resonator of the gas laser oscillation device according to the present invention; Fig. 2A is a plan view of the optical resonator illustrating optical axis alignment adjustment; Fig. 2B is a front view of the optical resonator illustrating the optical axis alignment adjustment; Fig. 3 shows a discharge tube; Fig. 4 is a view showing the fitness state with which a non-adjustable clamp is fitted into a mounting hole; Fig. 5 is a view showing the fitness state with which an adjustable clamp is fitted into a mounting hole; Fig. 6 is a cross-sectional view showing a visual inspection instrument for optical axis; Fig. 7 shows the visual inspection instrument which is fitted to a clamp; Fig. 8 shows a basic configuration of the gas laser oscillation device; Fig. 9A is a plan view showing a prior art optical resonator; Fig. 9B is a front view showing a prior art optical resonator; Fig. 10 is a cross-sectional view of a bending unit; Fig. 11 is a cross-sectional view of a visual inspection instrument for the bending unit; Fig. 12 is a cross-sectional view showing the visual inspection instrument is fitted to the bending unit; and Fig. 13 is a cross-sectional view showing the visual inspection instrument is fitted to the bending unit. DETAILED DESCRIPTION OF THE INVENTION Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. Referring first to Fig. 1, a discharge tube is designated 1. Designated 6 is a total-reflection mirror at one end of the optical resonance region; a partial-reflection mirror at the other end of the optical resonance region is 7; an optical bench is 14; 15a through 15c are clamps which are machined with a high accuracy standard; 16 are clamps which need adjusting in the conventional manner; 17 are clamps secured to the discharge tubes 1; 18 is a bending unit; 19 is a non-movable total-reflection mirror unit having a total-reflection mirror which is secured, but still with fine adjustment capability; 20 is a fine adjustment screw for the non-movable total-reflection mirror; 21 is a movable total-reflection mirror unit having an adjustable total-reflection mirror; 22 is an adjustment screw for adjusting the adjustable total-reflection mirror; 23 is a clamp which secures the total-reflection mirror 6 to one end of the optical resonance zone; and 24 is a clamp which secures the partial-reflection mirror 7 to the other end of the optical resonance zone. Among the above-mentioned components, clamps 15a, 15b and 15c are fixed to the optical bench 14, with clearance fit of which accuracy is far better than an optical axis misalignment level normally considered as acceptable, and these clamps thus need no adjustment. Since the non-movable total-reflection mirror unit 19 of the bending unit 18 is assembled to high accuracy standards in advance by means of a tool, no adjustment is required in principle once the non-movable total-reflection mirror unit 19 is installed on the bending unit 18. A fine adjustment screw is available on the non-movable total-reflection mirror unit 19 just in case the optical axis misalignment is not fully corrected with the adjustable total-reflection mirror unit 21 alone. Described next is the adjustment operation. Like the prior art already mentioned, clamps 17 are fixed to a discharge tube 1. Fig. 2 shows the view of the optical resonator in Fig. 1, but without both the discharge tube portion shown in Fig. 3 and the partial-reflection mirror 7 on one end of the optical resonator. The adjustment operation of the optical axis alignment is carried out under the setup shown in Fig. 2. An instrument 25 is installed onto the clamp nearest to the partial-reflection mirror 7, i.e., clamp 15a, as illustrated in Fig. 7, and another instrument 25 is installed onto the fourth clamp from the partial-reflection mirror 7, i.e., clamp 15b. In the same manner as the prior art, laser beam is directed to the instrument 25 on the partial-reflection mirror side. The laser device for the optical axis adjustment, such as a helium-neon laser device, is set up in position so that laser beam passes through each center hole 27a of both instruments 25. The axis passing through both centers of clamps 15a and 15b is hereinafter used as the reference optical axis. After another instrument 25 is installed onto one of clamps 16 which are located along the reference optical axis between the clamp 15a and the clamp 15b, that clamp 16 is adjusted so that laser beam passes through the center hole 27a of the instrument 25. Each of clamps 16 located along the reference optical axis between the clamp 15a and the clamp 15b is adjusted as above. Next, an instrument 25 is installed to the eighth clamp, i.e., clamp 15c. The adjustable total-reflection mirror 21 on the bending unit 18 is adjusted with the adjustment screw 22 so that laser beam passes through the center hole 27a on the instrument 25 installed on the clamp 15c. The above adjustment allows the incident laser beam fed through the mounting portion of the partial-reflection mirror 7 to reach the total-reflection mirror 6 at the other end of the optical resonator. Adjusting the remaining clamps 16 completes the optical axis alignment adjustment. The optical resonator is fully assembled by fitting the discharge tube units shown in Fig. 3 into the clamps. If three or more discharge tube rows are connected, with each row comprising two discharge tubes connected in series, each reference optical axis of adjustable total-reflection mirrors of a second bending unit and a third bending unit is set up by directing laser beam from the center of a clamp, nearest to the partial-reflection mirror, to the center of a fourth clamp from the partial-reflection mirror, and then each intermediary clamp 16 is adjusted for laser beam to properly pass. In the above description, the optical axis alignment is adjusted by using, as a reference, the clamp located near the partial-reflection mirror of the optical resonator and by feeding laser beam through that clamp. As a reference, however, a clamp located near the total-reflection mirror may be used. In such a setup, the partial-reflection mirror may be designated 6 and the total-reflection mirror may be 7 in both Fig. 1 and Fig. 2.

Claims: A gas laser oscillation device, comprising: m rows of discharge tubes (1) connected in series, m being 2 or larger, each row comprising a natural number n discharge tubes (1) connected in series, with clamps (15a, 15b, 15c and 16) disposed at each end of each neighboring series discharge tube to secure said series of discharge tubes (1) to an optical bench (14); at least one bending unit (18), secured onto the optical bench (14), for connecting said discharge tube rows in series, the bending unit (18) comprising a pair of total-reflection mirror units (19 and 21), one non-movable total-reflection unit (19) being substantially secured to the bending unit (18), and the other adjustable total-reflection unit (21) being movably mounted on the bending unit (18), the bending unit serving to fold the optical axis of the device from one row of discharge tubes to the next row of discharge tubes; and a total-reflection mirror (6), which is disposed at one end of the optical system made up of all discharge tube rows which are connected in series by the bending unit (18), and a partial-reflection mirror (7), which is disposed at the other end of the optical system; a first clamp (15a) nearest to the total-reflection mirror (6) or the partial-reflection mirror (7), and the other clamps (15b, 15c) which are 2·n-th clamp and an integer number times 2·n-th clamp from the first clamp along the optical axis (15a) being substantially secured to the optical bench (14) unmovably; and the remaining clamps (16) which are movable clamps, mounted on the optical bench (14). A gas laser oscillation device as defined in claim 1, wherein said non-movable clamps (15a, 15b, and 15c) are fixed to the optical bench (14) with clearance fit of which accuracy is far better than an optical axis misalignment level considered as acceptable. A gas laser oscillation device as defined in claim 1, wherein said non-movable total-reflection mirror unit (19) is secured to said bending unit (18), in a manner that a fine adjustment is still operative. An optical axis alignment method for aligning the optical axis of the gas laser oscillation device of claim 1, comprising the steps of: a) fixing the movable clamps (16), existing along a reference optical axis which passes through a center of the first non-movable clamp (15a) and a center of the second non-movable clamp (15b), to the optical bench (14) in a manner that all centers of the movable clamps (16) are aligned with the reference optical axis, an optical resonance zone being formed by the m rows of discharge tubes (1), with each row comprising n discharge tubes (1) connected in series, with the clamps (15a, 15b, 15c, and 16) disposed at each end of the discharge tubes in order to secure them to the optical bench (14), and the first non-movable clamp (15a) being located nearest to the total-reflection mirror (6) at one end of the optical resonance zone or to the partial-reflection mirror (7) at the other end of the optical resonance zone, and the second non-movable clamp (15b) being a 2·n-th clamp from the first non-movable clamp (15a); b) extending said reference optical axis by aligning said reference optical axis with a canter of the next non-movable clamp (15c) which is an integer number times 2·n-th clamp along said reference optical axis by adjusting only the movable total-reflection mirror unit (21) out of the two total-reflection mirror units (19 and 21) on the corresponding bending unit (18); c) fixing the movable clamps (16), existing along the extended reference optical axis, to the optical bench (14) in a manner that all centers of the movable clamps (16) are aligned with said extended optical axis; and d) repeating the above mentioned steps b and c until the last discharge tube row is adjusted.

Inventors: HONGU HITOSHI, HONGU, HITOSHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H01S3
IPC codes: H01S3