1. Field of the Invention
The present invention relates to a gas laser oscillating unit, in particular, a gas laser unit provided with a gas flow passage having a junction.
2. Description of the Related Art
In an axial-flow type laser oscillating unit, a gas flow passage of the unit has been improved, in which a laser medium or laser gas flows in an excitation part in order to generate a laser beam by discharging, a light reaction or chemical reaction. For example, in Japanese Unexamined Patent Publication (Kokai) No. 6-326379, a taper portion is provided on the inlet and outlet portions of a flow passage for a laser gas, in order to reduce the pressure loss of the passage. In Japanese Unexamined Patent Publication (Kokai) No. 9-199772, the shape of the front portion of an excitation part of a gas flow passage is configured in order to make the gas flow in a discharge tube a spiral flow, thereby stabilizing the discharge.
Further, in Japanese Unexamined Patent Publication (Kokai) No. 2003-283008 or Japanese Unexamined Patent Publication (Kokai) No. 2004-235517, two excitation parts are arranged on the same laser beam axis, and two gas flows collide with each other at a junction part between the two excitation parts. It is advantageous to merge the two flows from the two excitation parts, instead of having two separate flows, since the number of components of the flow passage may be reduced and the length of the non-excitation part may be shortened. Due to a reduction in the number of components, the cost of the laser oscillating unit may be reduced. Further, due to the shortened length of the non-excitation part, the efficiency of laser oscillation may be improved, since the energy loss of the laser beam is reduced.
FIGS. 5 and 6 are perspective views showing an example of the structure of a junction part of a laser gas of the axial-flow type laser oscillation, as described in Japanese Unexamined Patent Publication (Kokai) No. 2003-283008 or Japanese Unexamined Patent Publication (Kokai) No. 2004-235517. As shown in FIG. 5, a tapered gas flow passages 161a is arranged between the excitation part 103a and a junction part 123, and a tapered gas flow passage 161b is arranged between the excitation part 103b and the junction part 123. The two opposing tapered passages 161a and 161b are symmetric about an axis 152 extending through a center point 151 of the junction part 123 and perpendicular to a laser axis 104. In other words, the two tapered portions are plane-symmetric about a plane including the axis 152 and perpendicular to the laser axis 104.
Therefore, two gas flows (having the same flow rate and velocity) are generated in two flow passages, and then the two gas flows collide with each other at or near the center point 151. In this case, the state of the gas flow in the junction part 123 is unstable or easily varies. For example, the state of the gas flow at a given time t1 is represented in FIG. 5, and then the state of the gas flow at another given time t2 may be changed as shown in FIG. 6. In other words, in the state of FIG. 5, the gas flows 180a and 180b flowing from the −X excitation parts 103a and 103b are biased to the −X and +X directions, respectively, and merge in the junction part 123. On the other hand, in the state of FIG. 6, the gas flows 180a and 180b are biased to the +X and −X directions, respectively, and merge in the junction part 123. At this point, as shown in FIGS. 5 and 6, the X-direction is perpendicular to both the axis (or Y-direction) parallel to the laser axis and the longitudinal axis of a gas flow passage 162 (or Z-direction) arranged downstream relative to the junction part 123. In this example, the state of the gas flow is changed from time t1 to time t2, in other words, the state of the gas flow is unstable. Also, such an unstableness of gas flow, in two opposing gas flow passages constituting the plane-symmetrical structure, has been studied by numeric analysis, such as a finite element method of gas flow.
The laser gas, after flowing through the excitation part, is activated and has the property of absorbing the laser beam. Therefore, when the gas flow is unstable, the laser output and/or the shape of the laser beam mode may fluctuate. For example, in a laser machining process, the quality of a cut surface of a product may be deteriorated. Further, when the laser is used as a light source, the quantity of light may fluctuate.
The above Japanese Unexamined Patent Publication (Kokai) No. 6-326379 and Japanese Unexamined Patent Publication (Kokai) No. 9-199772 disclose ways to modify the gas flow passage. However, the ways are not directed to a technique for avoiding frontal collision of the gas flows as described in Japanese Unexamined Patent Publication (Kokai) No. 2003-283008 or Japanese Unexamined Patent Publication (Kokai) No. 2004-235517.